School Of Digital Photography: October 2014

Monday, 27 October 2014

Fisheye Lens

A fisheye lens is an ultra-wide-angle lens with an angle of view that is usually between 100 and 180 degrees and produces strong visual distortion intended to create a wide panoramic or hemispherical image.

Fisheye Lenses

Unlike wide angle and ultra wide angle lenses, a fish eye is an uncorrected lens so images produced with them have a characteristic convex non-rectilinear appearance.

For beginners it is easier to remember it this way; while using fish eye lenses; lines going around the center point are going to curve. And the further they are from the center point the more that they curve.

Circular Fisheye Lenses

Circular Fisheye Lens - Photo Courtesy Piero Fissore

A circular fisheye lens produces an image which is 180 degrees in all directions. Meaning it sees the world as a 180 degree hemisphere and projects the same as a circle on to the sensor and as a result you will have an image which has a 180 degree vertical angle of view, and 180 degree horizontal angle of view. As a result the corners of the frame will appear completely dark.

Full Frame Fisheye Lenses

Full Frame Fisheye Lens - Photo Courtesy Tom Bricker

These are improved versions of the above that fills the frame with image area. Unlike circular fisheye lenses, full frame fisheye lenses enlarge the image circle to cover the entire rectangular frame. The angle of view of pictures produced by these lenses measures 180 degrees when measured from corner to corner. They have a 180° diagonal angle of view, but the horizontal and vertical angles of view will be smaller.

For the 35 mm film format (full frame cameras), typical focal lengths of fisheye lenses are between 8 mm and 10 mm for circular images, and 15–16 mm for full-frame images.

NEXT: Aperture

Wednesday, 22 October 2014

Macro Lenses

The great thing about macro photography is that there is never any dearth of subjects. A macro lens will present you a whole new world of photographic opportunities right within your own backyard. Macro subjects are everywhere to be found, the intricate patterns in a flower petal, numerous bugs ,beetles and other insects, mushrooms, fungi etc. all make great subjects for macro photography.

Macro Photography

However the most important feature of a macro photograph is the amount of detail and sharpness it has; and attaining it requires a strong understanding of photographic concepts like focal length, magnification, sensor- size, depth of field, diffraction etc.

Magnification

When we speak about magnification of a macro lens we are referring to the magnification at the image plane, meaning the size at which an object will appear on the camera’s sensor in relation to its original size. For example if the size of the object on the image sensor is 50% of its actual size then the lens is said to have a magnification factor of 1:2 or 0.50X.

Photograph at .25x magnification

Photograph at 1.0x magnification

So greater the magnification factor of the lens the smaller the size of the subject with which you will be able to fill the frame. The two lens properties that determine the amount of magnification of a lens are focal length and focusing distance. The longer the focal length of the lens, the greater its magnification and the closer a lens could focus the greater its magnification.

Sensor Size and Magnification

Other than the magnification of the lens, one important factor that determines the size of the smallest object with which one can fill the frame is the sensor size of the camera.

macro photography magnification and sensor size

For example if a lens with a magnification factor of 1:2 or 0.05X is used to photograph a subject, even though the image formed by the lens on the image plane is the same, a smaller sensor will only capture the center portion of the image cropping out the rest. So the smaller the sensor the greater is the effective magnification. Thus everything else being the same, a smaller sensor is capable of photographing even smaller subjects.

Close up and Macro Photography

Any lens which has a minimum magnification factor of 1:10 or greater is called a close up lens and photography at those magnification is called close up photography. True macro photography is when one captures objects at life size (same size as the actual object) 1:1 magnification or higher. In general people use the term macro broadly to include anything from 1:10 to 1:1. However a lens is only categorized as a macro lens only if it is able to achieve magnification of 1:1 or greater.

Macro Focal Lengths

Macro lenses come in Normal, Short Telephoto and Telephoto focal lengths; one may choose the focal length appropriate for the type of subject and also depending on the working distance needed and the perspective one wish to achieve. Shooting closer to the subject expands perspective, while shooting from farther away compresses it.

Macro lenses with normal focal length (50mm for a full-frame sensor camera) achieves 1:1 magnification and provide a working distance of about 7 – 9 inches. Those with short tele photo focal lengths (100mm for a full-frame sensor camera) provide of about 12 inches while Tele photo macro lenses (200mm for a full-frame sensor camera) give an even greater working distance of about 19 inches.

Increased working distance helps in more than one ways. It allows one to shoot without getting much closer to the subjects that are easily scared away. The longer working distance lets one to easily light the subject.

Working Distance and Minimum Focusing Distance

Working distance means the distance from the front of the lens to the subject. It is an important consideration when choosing between macro lenses of different focal lengths. Generally at any given magnification, the working distance increases with focal length.

Minimum focusing distance is the distance from the focal plane to the subject when the lens is focused at its closest focusing point.

Lens Extension and Effective F Stop

We have seen earlier that when a lens is focused at infinity the lens elements are arranged closest to the image plane and when a lens is focused at nearby objects, such as in macro photography the lens elements are at extended further from the camera, the higher the magnification the farther the lens elements are.

This is called ‘extension’; for relatively lower magnifications the extension is very small so the lens elements remain at the expected distance of roughly one focal length from the sensor.

macro photography lens extension and effective f stop

As magnification increases to o.25x or higher, the lens elements move further away from the sensor and this make the lens behave as if having a higher focal length.

At life size or 1:1 magnification, the lens elements move out twice the focal length from the camera’s sensor.

macro photography lens extension and effective f stop

When you are shooting a subject at 1:1 magnification and at f/2.8 you will actually be getting results as if an aperture of f/5.6 was set on the camera.

This increase in effective focal length changes the effective f stop of the lens. With a change in the lenses focal length, the effective f stop increases , so it increases the depth of field , requires a longer exposure time and the lens also becomes susceptible to diffraction. So the lens now displays all the characteristics of a longer focal length lens and the focal length had indeed changed, it is only addressed as effective focal length because most cameras do not show the change in f stop in its settings. And since the camera's metering system automatically compensates for the drop in light when it calculates the exposure settings most people does not take notice of it.

Since the camera's metering system automatically compensates for the drop in light when it calculates the exposure settings most people does not take notice of it.

Depth of Field and Macro

Depth of field is one of the major factors influencing macro photography, It becomes shallower as the magnification increases, the higher the magnification the shallower the depth of field.

With magnifications of 1:1 or higher, one is working with depth of field of only millimeters. One technique; macro photographers use is to align their subject along with the image plane so as to get most parts of the subject in the plane of sharp focus.

Where sufficient depth of field is critical; photographers need to stop down the lens considerably and in such cases; it is better to know the diffraction limited resolution of your camera.

It’s a common belief that depth of field is more for cameras with smaller sensors. In one way it is true, for the same f stop a smaller sensor camera will have larger depth of field when compared to one with a larger sensor.

But it is to be noted that the larger sensor also could use larger f numbers before diffraction starts to get in and reduce picture quality. Results produced from both sensors at their diffraction limited resolution is comparable; both will have the same depth of field.

The advantage of cameras with smaller sensors is really in the shorter exposure time it requires to achieve the same depth of field.

Some interesting facts about Macro Depth of Field

At lower magnifications the available depth of field is distributed more towards the back of the plane of focus than to the front. But when is increased; this distribution of depth of field becomes evenly balanced towards the front and rear.

Depth of field is independent of focal length. A 50mm, 100mm, or 200mm lens set to the same f stop and at 1x magnification will all have the same depth of field.

Macro Photography and Diffraction Limit

Macro photographers are always looking for ways to increase depth of field in their pictures, and they do this by using higher f stops. But one thing to be aware of is that your lens is not sharpest at its narrowest apertures, in fact after a certain point higher apertures will only mean lower image quality due to diffraction.

Diffraction is more pronounced at higher f stops and is also influenced by the characteristics of your specific lens. To produce great macro photographs one should be aware of this phenomenon and also should be willing to trade diffraction induced softening for greater depth of field or greater sharpness for lesser depth of field depending upon the situation.

However when working at high magnifications always remember that it is the effective f-stop that determines the diffraction limit and not the one set by your camera.

Macro Lenses and Image Quality

The higher subject magnification achieved in macro photography also highlights the various imperfections in your camera lens including chromatic aberrations, image distortion and blurring. The problems will be more visible towards the edges of the frame than at the center.

This is one reason why people struggle to achieve great image quality at higher magnifications with non -macro lenses and when shooting with compact cameras in macro mode.

However macro lenses by design are tuned to achieve optimal image quality near its minimum focusing distance and thus produce great results.

NEXT: Fish Eye Lenses

Monday, 20 October 2014

Tele Photo Lenses

Lenses with focal lengths longer than that of Normal (approximately 40degree angle of view) are called tele photo lenses. Generally lenses which have a focal length of 70mm or more are termed tele photo lenses. Remember that focal lengths mentioned in this article are all for full frame sensors and if you camera has a crop sensor then you need to factor that into the equation.

Tele Photo Lenses

Types of Telephoto Lenses

Short Telephoto Lenses (Focal lengths from 85mm - 135mm)

Short Tele Photo Lenses

Short telephoto lenses comprise focal lengths from 85mm to 135mm; they are normally very compact and lightweight lenses ideal for handheld shooting of portraits and candid shots. The short tele photo focal length is the most preferred focal length for shooting portraits as it brings out the best proportions in a human form.

Medium Telephoto Lenses (Focal lengths from 135mm - 300mm)

Medium Tele Photo Lenses

Lenses with focal lengths from 135mm – 300mm are termed as medium telephoto lenses, they are more expensive and bulkier compared to short tele photo lenses and are commonly used to shoot action and sports.

Super Telephoto Lenses (Focal lengths from 300mm+)

Super Tele Photo Lenses

Super telephoto lenses are the ones with a focal length greater than 300mm, they are mostly used by professional wildlife photographers and also by some sports photographers. They are very specialized piece of equipment and so they are very expensive and also weigh much. One will need super heavy duty tripods and specialized tripod heads like the gimbal heads to make the most out of these heavyweights. However they lets you get as close to the action as possible without intruding your subject’s private space and putting your life at risk. Super tele photo lenses are also used for astrophotography.

Why use a telephoto lens?

A common misconception most beginner photographers have about telephoto lenses is that are just for capturing subjects at a distance. And are only to be used in situations where you can’t get physically close to the subject. While this is one of the major advantages that a telephoto lens gives the photographer, the ability to photograph objects from a distance, it is the control of perspective that is the decisive factor. The distance from which you shoot your subject changes the perspective of your photos. Tele photo lenses lets the photographer normalize the size and distance between near and far objects, thereby making the depth of field look much shallower.

Telephoto Lens and Perspective

The narrow angle of view provided by telephoto lenses helps normalize the relative size and distance when comparing near and far objects. Meaning even though nearby objects actually appear larger in reality; when viewed through a telephoto lens both nearby objects and objects that are much further appear of similar size. This effect is known as "foreshortening" or "perspective compression". It is to be noted that normalizing the relative size too much would make the scene flat and uninteresting as human eyes generally expect closer objects to appear little larger.

A telephoto lens could also make the distance between objects appear compressed. Meaning they can make objects that are physically miles apart to look as if they are on the same plane. A much powerful tool if one needs to emphasize the number of objects, or to enhance the appearance of congestion.

Another common misconception about telephoto lenses is that they affect the perspective, however just as we discussed in case of wide angle lenses, perspective is only affected by the distance from the camera to the subject. Normally when shooting with a tele photo lens one is much further away from the subject which does affect perspective and not any peculiarity of the lens as such.

Shooting Far Away Subjects

With its very narrow angle of view a telephoto lens enables the photographer to bring small and distant objects closer, thus making it possible to photograph candidly without the subject being aware of the camera, which could significantly alter its behavior. This is useful especially for candid portraits and also when shooting wildlife. Telephoto lenses also let the photographer selectively compose his/her frame so as to make simple and focused compositions. The power to exclude what is not required in a frame presents unlimited creative potential to the creative mind.

Shooting Landscapes with telephoto lenses

We all grew up hearing that "a wide angle lens is for landscapes" and "a telephoto lens is for wildlife”. The logic behind this is that wide angle lenses exaggerate the sense of depth and spaciousness is an important quality of landscapes which makes wide angle lenses the perfect choice for landscape photography.

However it is to be noted that very powerful and effective compositions can be made with the "inappropriate" type of lenses. Telephoto lenses compress the sense of depth and so to use them to shoot landscapes require adopting different techniques. Remember in case of tele photo lenses, less is more, keep your compositions simple, cut out the seemingly unimportant elements and concentrate on the most visually striking elements thereby adding impact. A common telephoto technique to improve the sense of depth is to compose the scene so that it's comprised of layered subject matter at distinctly different distances.

Focusing and Telephoto Lenses

While using telephoto lenses, it is of utmost importance that you focus on the chosen area with pin point accuracy. The longer the focal length the more accurate your point of focus needs to be. The primary reason for this is because when shooting with telephoto lenses you will be working with much shallower depth of field, and the magnification of the lens also enlarges the out of focus area thereby increasing blur in those areas.

Telephoto lenses are easier to work with the focus and recompose technique as one is shooting at a distance from the subject chances of errors are less. Preferred technique of most photographers is to use the central autofocus point to achieve focus, lock the focus (by keeping the shutter button half pressed) and recompose before you press the shutter fully down.

Combating Camera Shake

The longer the focal length the shorter the exposure time required to get a sharp shot. Camera shake is more pronounced with longer focal lengths and to reduce it you need to either use faster shutter speeds or hold your camera steadier or a combination of these.

One might need to use a larger aperture (if the lens used permits it) or increase the ISO of the camera. The compromise is with a wider aperture one loses depth of field and with a higher ISO setting there will be more noise in the images. One could lean on a stable object or use a monopod or a tripod to make the camera more stable.

Telephoto lenses and depth of field

Telephoto lenses do not have less depth of field. If you are magnifying your subject by the same amount both telephoto and wide angle lenses will give you the same depth of field. Telephoto lenses have a reputation of producing shallow depth of field, however it is due to the fact that while using tele photo lenses, people magnify their subjects more and they also shoot from further away thus the subject ends up filling more of the frame and so this higher magnification is what causes the shallower depth of field. As telephoto lenses enlarges the background in relation to the subject, It also does enlarge the out of focus regions in an image (bokeh) thereby giving the appearance of shallower depth of field.

NEXT: Macro Lenses

Sunday, 19 October 2014

Wide Angle Lenses

We have seen that lenses that replicate the view that human eye normally sees are called normal lenses. Wide angle lenses are the ones that have a wider angle of view than normal lens (shorter focal length).

Wide Angle Lens

Ultra Wide Angle Lenses

Generally lenses in the focal length of about 35mm – 24mm is termed wide angle and the ones that are even wider than 24mm is considered ultra wide angle lenses. In case of point and shoot digital cameras wide angle is when the lens is completely zoomed out, but ultra-wide angle is only possible with a special lens adapter.

Ultra Wide Angle Lens

A wide angle lens is a powerful tool in any photographer’s arsenal as it could be used to exaggerate depth and relative size (perspective) in a picture. But to get great results from wide angle lenses is a tough job and to do that one must first learn how to use them right.

Getting it all in

A common misconception most beginner photographers have about wide angle lenses is that they are primarily used when one wants to capture all of the subjects in a single frame and conditions does not permit you to move away from the subject so as to use a lens with a narrower viewing angle.

using wide angle lenses to get the whole picture

Well it is certainly one of the situations that call for the use of a wide angle lens. But a wide angle lens could do lot more than that. In fact a wide angle lens is commonly used by expert photographers when they want to get really close to their subject. One would wonder why?

it’s because wide angle lenses have a really wide angle of view and they generally have very short minimum focusing distances, meaning you could get really close to a subject and still have it in sharp focus with much of the background also visible thus giving the photographer much choice to play with perspectives.

Wide Angle Lenses and Perspective

Another common misconception about wide angle lenses is that they affect perspective. But in reality perspective is only influenced by the position of the camera in relation to the subjects. Using wide angle lenses will make you to move much closer to the subject and that does affect perspective and not the lens as such.

wide angle lenses and perspective

With the wider angle of view provided by wide angle lenses, It is possible to make nearby objects to appear gigantic and objects that are further away to appear much smaller and distant. Objects that are further only comprise a much lower fraction of the total angle of view. Photographers use this exaggeration to create emphasis to objects in the foreground while also capturing expansive backgrounds.

However when playing with perspective it is necessary to give attention to certain elements.

Get as close to the nearest subject as possible (usually position the nearest object at the nearest focusing distance of the lens).
Carefully compose your picture. Extremely close objects can shift by a huge margin with a slight movement of the camera.
Take extra caution while photographing people up close with a wide angle lens, else some of their features can become greatly out of proportion.

Converging Vertical Lines

Lenses when they are pointed above or below the horizon cause parallel vertical lines to appear as if they are converging. All lenses does this but the effect is more pronounced in case of wide angle lenses as a vast expanse of lines are visible with a wider angle of view. Also when using a wide angle lens, even minute changes in composition will shift the location of the vanishing point by a huge margin there by altering how sharply lines seem to converge in the image.

How to prevent vertical lines from converging

The best way to prevent vertical lines from converging is by using a tilt shift lens to control perspective. Only problem with them is that they are very specialized piece of gear so they are pricey and to use them, one need technical knowhow to get the desired results.

Aiming your camera closer to the horizon will reduce the effect to a great extent, however you will need to crop your frame later to get the desired perspective meaning you will lose resolution.

You could also move away from the subject and use a lens with a much longer focal length thereby minimizing the effect, however this is not always convenient or even possible and it also alters the perspective.

Finally you can use image editing software such as Photoshop to distort the picture so as to make vertical lines straight. The drawback to this method is also loss of resolution.

Managing Light Across A Wide Angle

When shooting with ultra wide angle lenses, the variation in the intensity of light across an image becomes an important factor. Human eyes will adjust to the changing brightness as we look in different directions, but when determining a photographic exposure much care should be taken as uneven light can cause some parts of the image to be over exposed while leaving some other parts underexposed.

A common example is when photographing a sunset the sky will be much brighter than the water, so if you expose for the sky the water will be under exposed and if you expose for the water sky will be over exposed. To manage differences in light levels like this photographers make use of graduated neutral density filters (GND filter). Read more about Dynamic Range and Graduated Neutral Density Filters.

Another major concern is lens flare, as the sun is more likely to be in the frame (due to the ultra-wide angle of view). Also it is very difficult to use lens hoods effectively as it should let in image forming light from across a very wide angle.

Using Polarizing Filters with Wide Angle Lenses

The influence of polarizing filters varies depending on the angle of the subject in relation to the sun. A polarizer has maximum effect when the camera is facing at a direction which is 90 degrees from the sun and has minimum effect when the camera is facing either directly into or away from the sun. When shooting with an ultra-wide angle lens, one edge of your frame might be at 90 degrees to the sun where it has maximum polarization effect while the other edge might be facing into or away from the sun where the filter has minimum polarization effect. Thus different degrees of polarization will be visible across a single picture which is undesirable and so it is generally not recommended not to use a polarization filter on wide angle lenses.

Wide Angle lenses and Depth of Field

It is yet another misconception that wide angle lenses produce more depth of field than tele photo lenses. However it is not true, if you magnify your subject by the same amount then both wide angle and telephoto lenses will produce the same depth of field. It’s only that people rarely get as close to their subjects with wide angle lenses as they do with tele photo lenses and this causes the difference in depth of field.

Tips to Get the Most out of your Wide Angle Lenses

Subject Distance

Getting as close to your subject as possible is the critical part, an ultra-wide lens shines when you physically immerse yourselves amongst your subject.

Position

With tele photo lenses it’s the direction which you point the camera that is important but with ultra wide lenses it is the position of the camera that is important. Even slight changes in camera placement could have a huge impact on composition.

Watch your edges

Carefully watch what’s happening at the edges of the frame at all times.

Organization - establishing near far relationship

Long lenses compress perspective they seem to squeeze everything from objects very near to objects very far into looking like it's on the same plane. Ultra wide lenses do the opposite they expand the apparent depth of an image by pushing back the background (since you have to get close) and pulling near objects even closer. Carefully place near and far objects to achieve clear compositions.

The Art of Exclusion

Unlike painting, photography is an art of exclusion, if you do not take special care and frame your shots carefully everything gets into the frame irrespective of the fact that whether it is adding value or taking away from the picture.

Perspective

Be aware of converging verticals at all times, if you wish to avoid it in your pictures make sure you point your camera at the horizon, and if you wish to use the effect be fully aware how its influencing your pictures.

Distortion

Just like converging lines, be also careful about two of the most common issues with wide angle lenses namely edge and barrel distortion.

Alignment

An ultra wide lens exaggerates even the slightest misalignment between film plane and subject plane. Be aware of this so that you can use this to your advantage.

Sucked-out Corners

The corners of ultra-wide shots look as if someone printed the image on a rubber sheet and pulled-out the sides and corners. If photographing people, beware that they'll look fat on the sides if, or skinny if they're lying down, since the sucking stretches things towards the edges and especially the corners.

Expanding Space

An ultra wide lens gives you the ability to exaggerate depth, making interiors seem more spacious. It pushes the back wall and everything at a distance further away and thus makes interiors look many times bigger than they actually are.

NEXT: Tele Photo Lenses

Saturday, 18 October 2014

Normal Lens

Human eyes see the world around us at about 40 degree angle of view i.e. without using our peripheral vision. Lenses that could reproduce a field of view that corresponds approximately to that of normal vision with no perspective distortion are called normal lenses.

Normal Lens

We have already seen that sensor sizes affect the angle of view and therefore there is no one single focal length that could be termed as normal. Instead normal focal length for each sensor size is different.

Normal Lens and Sensor Size

To find out what focal length should be considered normal for a camera we need to consider the sensor size of the camera. Focal length which is equal to the diagonal length of the sensor will be the normal focal length for that camera.

For example

In case of full frame cameras:

Normal Lens and Sensor Size

Sensor size = width 36mm, height 24mm and a diagonal measurement of 43.3mm

So any lens that produces an angle of view of approximately 43 degrees could be considered as normal lens for the full frame format. That is why 50mm lenses which is very close to 43.3mm is considered as normal lenses.

In case of cameras with APS size sensors

Sensor size = width 22.7mm, height 15.1mm and a diagonal measurement of 27.3mm

Lenses close to the angle of view of 27.3 could be considered as normal. That is why 35mm lens which is close to the 27.3mm is considered as normal lenses for cameras with APS size sensors.

In case of cameras using Micro four Thirds size sensor

Sensor size = width 18mm, height 13.5mm and a diagonal measurement of 22.5mm

So lenses close to 22.5mm could be considered normal lens for micro four thirds format. Either 20mm or 24mm which are two common focal lengths could be considered.

Now that we know what normal lenses are it is easy to figure out other types of lenses. Lenses which have an angle of view wider than normal lenses are called wide angle lenses and lenses which have an angle of view narrower than normal lenses are called tele photo lenses.

We will discuss about wide angle lenses in the next article.

NEXT: Wide Angle Lenses

Friday, 17 October 2014

Angle of View of Camera Lenses

Angle of view of a lens is what the lens sees or simply what you are able to see when looking through the viewfinder. Angle of view changes according to the focal length of the lens mounted on the camera. The longer the focal length of the lens; the narrower the angle of view and shorter the focal length wider the angle of view.

Focal Length and Angle of View of Camera Lens

Lenses with long focal lengths are called tele photo lens and that of short focal length are called wide angle lenses. When shooting a subject from the same distance, a wide angle lens which has a wide angle of view will capture a large area making the subject relatively smaller in the picture and a tele photo lens which has a narrow angle of view will capture only a small portion of the scene making the subject seem much larger.

Angle of view can be measured vertically, horizontally or diagonally and it changes with sensor size. Back in the ‘film days’ what the lens used to see (angle of view) was said to be the focal length of the lens.

I.e. angle of view = focal length; for 35mm film or full frame digital cameras.

But with cameras that use a sensor smaller than full frame, the focal length of the lens need to be multiplied with the crop factor to get the angle of view of the lens.

For example a 100mm lens mounted on a crop sensor camera with a crop factor of 1.6 x.

Angle of view = focal length 100 * crop factor 1.6 = 160

So for cameras using a crop sensor the angle of view could only be calculated; if sensor dimensions are known.

In case of zoom lenses where the angle of view changes with zoom. For example an 18 – 55mm zoom lens has the widest angle of view at 18mm and narrowest angle of view at 55mm and also covers everything in between.

Classification of Lenses according to Angle of View

Based on their angle of view lenses could be broadly classified into three categories. Normal Lens, Wide angle Lens and Tele Photo Lens. In the next article we will discuss normal lenses in detail.

NEXT: Normal Lens

Thursday, 16 October 2014

Focal Length of Camera Lens

What is Focal Length?

Focal Length of Camera Lens

When light rays pass through the camera lens there is one point where they all converge before going on and making an inverted image on the sensor; this point where the rays converge is called Nodal Point. Focal length is the distance from the Nodal point to the Image sensor.

Why is Focal Length Important?

It is the focal length of a lens that determines how wide its field of view is or in other words how wide a lens is. Shorter focal lengths create a wide angle of view and so lenses with short focal lengths are called wide angle lenses. Similarly lenses with longer focal lengths create a narrow angle of view and so they are called telephoto lenses.

Effect of Focal Length on Subjects

In lenses with shorter focal lengths (wide angle lenses) the light rays converge closer to the image sensor and this in turn makes subjects appear smaller. And in longer focal length lenses light rays converge further away from the image sensor thus making the subject appear much bigger (greater magnification).

Focal length of Lens and Perspective

Creative control of perspective is without doubt a powerful compositional tool in photography and is often the number one factor based on which the photographers choose which focal length lens to use (assuming there is no space limitation and the subject could be photographed from any position).

It is a common misconception in photography that focal length determines the perspective of an image. However this is not true; perspective only changes with one's location relative to their subject (perspective changes if you move closer or farther from the subject).

If the photographer is filling the frame with the subject; then wide angle and telephoto lens will produce different perspectives because in order to fill the frame with a wide angle lens the camera need to be positioned much closer to the subject than when shooting with a tele photo lens and this changes perspective, the wide angle lens will exaggerate or stretch perspective, whereas the telephoto lens will compress or flatten perspective.

If one is photographing a subject or scene from the same distance both wide angle and telephoto will produce the same perspective. If you crop your wide angle frame to match the output of your tele photo lens then you will have similar results.

There are some other factors influenced by the focal length of a lens.

Telephoto lenses are more susceptible to camera shake as even minute hand movements get magnified as the focal length increases, the longer the focal length greater this effect.
Wide angle lenses are typically more resistant to lens flare than tele photo lenses. This is because lens designers assume that sun is more likely to be in the frame when using a wide angle lens due to its wider angle of view and so they design them to reduce the effect.
Medium and telephoto lenses generally yield better optical quality for similar price ranges.

Focal length and Sensor Size

Traditionally SLR camera lenses were made to fit the 35mm film format, it is still the standard with which most lenses are manufactured, recently many camera manufacturers have introduced lenses especially for the crop sensor cameras. Canon’s lenses for the crop sensors are called EF-S lens and Nikon’s lenses for crop sensors are called DX lens.

It should be remembered that in this article we are only referring to lenses designed for the 35mm format cameras.

When a lens designed to work with the 35 mm format camera is used with a full frame DSLR (which has a sensor size equivalent to the 35mm film) it produces the intended angle of view which could be referred to as 1.0x. So a 100mm lens will produce an angle of view of

100 * 1.0 = 100mm

But when the very same lens is mounted on a crop sensor camera with a crop factor of 1.6 the angle of view of the lens changes accordingly as we are only capturing the center portion of the image formed by the lens and cropping out the borders. To find out the effective focal length all we need to do is to multiply the focal length of the lens with the sensors crop factor so our angle of view will be

100 * 1.6 = 160mm

A lens with the same focal length when used with different sized sensors produces different angle of views. So focal length is not the same thing as angle of view, they are two separate distinct things. So whenever focal length is discussed the size of the sensor should also be considered as the same lens will act differently on different cameras.

Focal Length and Rule of Thumb for Handholding the Camera

Focal length of the lens used has a significant impact on how easy it is to achieve a sharp handheld photograph. Longer focal lengths require shorter exposure times to minimize blurring caused by camera movement as vibrations are magnified greatly with distance.

The one over focal length rule is a rule of thumb used by photographers to calculate the minimum shutter speed required for getting sharp handheld shots. It states that for a 35 mm camera, the shutter speed needs to be at least as fast as one over the focal length (of the lens used) in seconds.

So when shooting with a lens of 200 mm focal length on a full frame camera, the exposure time needs to be at least 1/200 seconds.

However it is just a general rule, some people have much steadier hands than others and will be able to take sharp pictures while handholding the camera at much lower speeds. Also when calculating the focal length of the lens one needs to consider crop sensors and effective angle of view.

So when same 200 mm lens is used on a crop sensor camera with a crop factor of 1.6x the angle of view now becomes 200 * 1.6 = 320mm and thus minimum shutter speed for handholding becomes 320mm.

Zoom Lenses and Prime Lenses

When lenses were first made, they we all fixed focal length lenses. Changing lenses were one big hassle especially when shooting dynamic scenes or subjects such as when doing photojournalistic work or when shooting action – sports / children. Thus lens designers came up with a lens that could vary its focal length within a pre-defined range thus allowing the photographer to achieve a variety of compositions or perspectives without changing lenses. This new breed of lenses that could vary their focal length was called Zoom lenses and the original fixed focal length lenses were now addressed as Prime lenses.

The major advantages of zoom lenses were that they enabled the photographer to change both composition and perspective. The photographer could change the composition without shifting his / her position with relation to the subject by simply zooming in or out. And he / she could change the perspective by either zooming out and getting closer to the subject (exaggerating subjects near to the lens in relation to background) or by zooming in and moving farther from the subject (compress the scene).

Although Zoom lenses offered many advantages, most of the earlier zoom lenses were no match to their prime counterparts when it came to image quality. But advances in lens design and technology has now made it possible to make Zoom lenses that could deliver similar results to that of prime lenses.

Prime lenses still have certain advantages over Zoom lenses:

They are fast (wider apertures) making them the ideal lens for low-light sports/theater photography, and in situations where a shallow depth of field is necessary.
They weigh much less than a zoom lens of similar focal length, if only a small portion of the focal length range of a zoom lens is necessary to make the shot, then a prime lens with a similar focal length will be a significantly smaller and lighter choice.
Prime lenses are also cheaper when compared to Zooms. Even an inexpensive prime lens could deliver equal or better image quality to that of a high end zoom lens.

One common mistake a lot of people make is to take zoom for tele photo. A zoom lens just means it changes from one focal length to another. So if you say I really need a zoom lens to take a picture of the bird that’s really far away, actually what you mean is that you need a tele photo lens. As a zoom lens could also be a wide angle zoom. E.g. Canon 10-22mm.

Compact Zooms

Many point and shoot cameras released recently to the market have powerful zoom lenses. But one thing to be understood is that when a camera is said to have 10x zoom, it actually is referring to the ratio of its longest and shortest focal lengths. So larger zoom designations like 15x or 20x need not necessarily mean narrower angle of view, they could simply be wider when fully zoomed out.

Also digital zoom does not mean that the camera has more zoom range. Digital zoom works by taking a small portion of the sensor image and enlarging it using interpolation it is just like cropping your images and enlarging them in Photoshop.

NEXT: Angle of View of Camera Lenses

Sunday, 12 October 2014

Camera Lens Basics

The ability to use interchangeable lenses is undoubtedly the most important advantage of a DSLR. However there are many choices when it comes to choosing the right lens for a job; a fair understanding about camera lenses and their properties will definitely help to exercise more creative control over your digital photography.

camera lens basics

Which lens is to be used to photograph a particular scene or object depend upon by many factors like focal length, angle of view, size and weight, lens speed, apertures, required image quality etc.

So in this section of our basic photography course, we will discuss the following characteristics of camera lenses.

Focal Length
Angle of View
Lens Speed
Apertures
Depth of field
Image quality and
Lens sharpness

What is a camera lens?

A camera lens is in fact a collection of many different types of lenses and coupled with an aperture mechanism. Each element serves different functions and their combined role is to bend the light rays entering the lens in many different ways so as to focus them all precisely at the image sensor to form a sharp image of the scene in front of the lens.

Some of the lenses inside are grouped together;
Some are fixed in position
While others are floating elements (meaning their position change).

Why they move?

Elements inside the lens move to aid the camera in focusing, to zoom, or to assist in the optical image stabilization process.

Lens design is one complicated affair which involves solving many challenges. One of the major challenges is to make the lens sharper not only in the center but also across the entire width of the photograph including the extreme edges. The goal is to minimize aberrations, distortions, minimize flare etc. while still utilizing the fewest number of lens elements.

At first thought the function of a camera lens seems simple but it isn’t, lens design is one complicated affair which involves solving many challenges. One of the major challenges is to make the lens sharper not only in the center but also across the entire width of the photograph including the extreme edges. Matters get even more complicated when designing a zoom lens, as the lens has to focus precisely across various focal lengths.

The complexity of lens design is beyond the scope of this article so we will focus more on other aspects that really matter to us as photographers. The very first thing one should be aware of any lens is its focal length; so that is what we are going to discuss next.

NEXT: Focal Length

Saturday, 11 October 2014

Hybrid Viewfinder Technology

In a hybrid viewfinder camera there is the traditional rangefinder type view and then there is an lcd panel to the side of the viewfinder which shows the electronic view from the lens, a half mirror positioned inside the viewfinder lets you choose either view.

hybrid viewfinder technology

The photographer can switch between the optical and the electronic viewfinders simply by pressing a button and thus could choose the best method for any shooting conditions. While most photographers would prefer the optical view as their primary choice the electronic viewfinder could provide them with a host of useful information like aperture, shutter speed, white balance and more. Electronic view could also be zoomed in for checking details or focusing accuracy.

The advantage of such a system are many, main one is being able to see exactly what the lens sees just like in a DSLR camera. Rangefinder cameras traditionally did not have a way to know if there is any obstruction in front of the lens, or know the angle of view etc. but with the new hybrid technology this no longer is an issue.

Now that we have discussed about the various types of digital camera and also their functioning, it’s time for us to move on to our section on lenses.

NEXT: Lenses

Friday, 10 October 2014

Translucent Mirror Technology

Traditional DSLRs rely on the mirror located in front of the sensor to reflect light to the focusing screen and from there to the viewfinder. The mirror used is 100% reflective (meaning it’s opaque). When the shutter button is pressed, the mirror flips up and the actual exposure is made; during the exposure, as the mirror is flipped up there is no light being reflected back towards the focusing screen or the auto focus sensors. As a result the viewfinder blacks out and auto focus sensor also stop receiving any information during that time.

Secondly the mirror which is located so close to the sensor inside the camera body causes vibrations when it moves up and down. This could cause a similar effect like that of camera shake and cause pictures to look shaky or blurry.

Thirdly if this mechanism is altogether eliminated the camera’s operation would become much simpler and faster and the physical size of the camera (depth) could also cut down considerably.

Translucent mirror technology

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Recently Sony, another pretty big player in the digital imaging world has come up with a revolutionary new product called ‘translucent mirror technology’. Instead of a flapping mirror they now employ a translucent mirror which is a fixed one. What it does is to reflect approximately 1/3rd of the light to the phase detection auto focus sensor and let the rest 2/3rd of light to pass on to the image sensor.

Advantages of Translucent Mirror Technology

The advantages of this system over conventional mirror system are many.

The camera’s viewfinder does not go black during an exposure meaning you get to see exactly what you are shooting.

Similarly the camera’s auto focus sensor receives 100% of the information, without any blackouts, which is extremely helpful in situations that require continuous focusing.

Lack of a flapping mirror means less vibration enabling you to handhold at even slower shutter speeds than traditional DSLR cameras.

As there is less mechanical parts to think of cameras using translucent mirror technology is capable of achieving Faster frame rates than their mirrored counterparts.

Disadvantages of Translucent Mirror Technology

Now let’s discuss what could be the downside of such a system.

The major concern photographers raise is; the efficiency of such a camera system rests on the quality or resolution of the LCD screen inside of the electronic viewfinder.

The performance of this technology under low light, wet and dusty circumstances could be assessed only in actual field-work.

NEXT: Hybrid Viewfinder Technology

Thursday, 9 October 2014

Digital Single Lens Reflex (DSLR) Cameras

Single Lens Reflex (SLR) cameras are popularly known as DSLR – Digital Single Lens Reflex cameras. Canon and Nikon are the two biggest manufacturers of DSLR cameras, followed by Sony, Pentax and many others.

DSLR cameras

They typically have much larger sensors than other types of digital cameras, have interchangeable lenses and have an optical (pentaprism or pentamirror) viewfinder and also electronic view on the back LCD panel.

How Does a Camera Work?

In DSLRs the light coming in through the lens is reflected on a mirror to form an image at the focusing screen, the light is then reflected off the penta- prism to the viewfinder.

Dslr camera parts

The ability to look through the viewfinder and see exactly what the lens sees is considered one of the most important advantages of a DSLR camera. By looking through the lens you will be able to tell the angle of view, whether there is a filter on the lens and its effect on the scene, you can even check the depth of field by pressing the depth of field preview button.

When the shutter button is pressed the mirror flips up and lets the light fall on the image sensor. Once the exposure is made; the mirror comes back to its original position.

DSLR camera functioning

One big disadvantage of the DSLR camera is that; at the time of exposure you cannot see through the camera. Even though it is only going to be a fraction of a second. So if you really need to time something; anticipate the moment and release the shutter just before it happens. Waiting to view the action before pressing the trigger may cause you to miss the chance forever to capture it in camera!

Now let us discuss the advantages and disadvantages of the DSLR Camera.

Advantages of a DSLR Camera

1. Optical Viewfinder

DSLRs have an optical viewfinder which lets you see through the lens, the more expensive models sport pentaprism and the budget ones do it with pentamirror. Essentially a dslr is a WYSIWYG (What you see is what you get) device, simple and efficient.

2. Full Manual Control

Unlike other digital cameras; where you have limited control over the many variables like shutter speed, aperture, iso, white balance etc. a dslr gives you complete control over all aspects of photography including focus.

3. Better Image Quality

Typically dslrs have much bigger sensors than other types of cameras; resulting in better image quality. It gives you the ability to shoot in RAW, and also has the capability to capture more dynamic range.

4. Better Low light performance

When compared to other digital cameras; dslr generates much less noise even at high iso. This is partly due to the larger sensors and other features.

5. Better Quality Optics

Generally lenses made for professional dslr cameras are of much higher quality than those made for other types of cameras.

6. Ability to use special lenses

A dslr with its ‘interchangeable lens feature’ could use any type of lens to match the scene; in addition to ultra wide angle, super tele- photo and macro lenses, it could also make use of specialists’ lenses like the ‘tilt shift’ and ‘fish eye’.

7. Faster Operation

They are built for speed; hence are faster in every aspect like start up time, focusing speed, frame rate, shutter lag etc.

8. Ability to use various accessories like remote release; filters etc.

There are many accessories available for dslrs like polarizing filters, neutral density filters, graduated neutral density filters, UV filters, infrared filters and so on. Owning and mastering the use of accessories alone can lift one amateur getting graduated in to higher levels in the art of photography.

9. Better Battery Life

Dslr batteries last really long; they enable you to take more pictures with each charge than any other type of cameras.

10. Better construction

DSLRs are built to last. Professional DSLR body is made of magnesium-alloy and can take a lot of physical abuse, while other types of cameras which are mostly made of plastic would quickly break down.

11. Better Weather Sealing

Weather sealing both on the body and the lenses enable DSLR cameras to function effectively under challenging weather conditions. Higher-end DSLRs can withstand all elements of nature like dust, moisture, rain, snow and severe cold.

12. Ease of operation

The large sized DSLRs have some advantages, they have bigger buttons and controls that let you directly access important functions instead of digging it out from menu. The large sized buttons also avoid chances of accidentally getting pressed.

13. Ability to use Dedicated Flash Units

There are dedicated professional-quality flash units from all major manufacturers; that could be used on or off camera. They render better control over lighting and are highly advanced flash units with much faster recycle times, ETTL capabilities and the ability to sync wirelessly give a photographer endless options to play with.

14. Complete Control over Depth of Field

The combination of larger sensor size and the ability to use interchangeable lenses (wider apertures and also longer focal lengths) helps one to have complete control over the depth of field in his pictures; while other cameras struggle at achieving shallow depth of field.

Disadvantages of a DSLR Camera

1. DSLRs are Costly.

The decision to own a dslr with required paraphernalia could be expensive. Professional quality lenses cost as much or in certain cases multiple times more than the cost of the camera body. Filters, memory cards, spare battery, and then a camera bag to carry them, all add up to the final costs.

With a dslr camera the possibilities are endless and people keep on buying equipment and accessories one after other throughout their life, as their skill level advances or as they specialize in certain types of photography

2. Complexity.

Only people who are serious about their photography and who are willing to invest the time and effort required to master the fundamental principles of photography should buy a DSLR. For casual shooters, a point and shoot or a mirror less is a much better option, you will get much better pictures with them than your DSLR if you really don’t know what you are doing.

3. Recurring Maintenance Expenses.

Maintaining a DSLR and a set of lenses could be costly especially if you are living in tropics, near the sea shore or in areas where the atmosphere humidity or dust levels are pretty high. Chances are more of dust and moisture sneaking in to the camera and soiling the sensor while changing lenses. Moisture could also cause fungus to grow inside of the lenses and also on the sensor. Getting the sensor or the lenses cleaned off dust or of fungus is an expensive business and is also a recurring expense.

4. Weight and Size.

DSLR cameras are much bigger and heavier than most other types of digital cameras. Not to mention the weight of all the lenses and accessories that you need to carry along. If you are the type of person who carry the camera around for long periods, then it’s advisable that you get a broad strap.

5. Noise

The action of the mirror and the shutter in DSLR camera produces much more noise (sound of moving physical parts). It could be an inconvenience in certain situations. Some newer cameras now have a special “Quiet” mode which helps to lower the noise.

NEXT: Translucent Mirror Technology