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Pentax User Archive: Through The Eyes Of Pentax

For 50 years the single-lens reflex has proved to be the camera of choice for the majority of serious photographers. John Riley tells us why.

Posted: 18/01/2013 - 00:00

The 10-17mm fisheye zoom has a 180 degree angle-of-view which creates this effect.

The single-lens reflex (SLR) is so popular because it allows the photographer to see exactly what will be recorded on film or sensor, unlike a non-SLR camera which could produce a photograph completely different to what was shown through the viewfinder. The SLR is capable of almost anything, providing the right lens is attached to its lens mount.

The Pentax K-bayonet is one of the most versatile of all camera mounts devised. It enables us to use all the Pentax lenses right back to the screw thread Takumars of the 1960s, although earlier lenses without electronic contacts have limited functionality on digital SLRs. Since the advent of electronic contacts in the mount from the A-series onwards all lenses will be fully functional, although manual focus lenses will have to be focused manually.

The way this mount has retained such a degree of backwards compatibility, while evolving to cater for current needs, is something quite remarkable and all credit is due to those early Pentax designers.

Mechanics aside, glass and coatings are critical features and Pentax’s Super-Multi-Coating (SMC) has been their best since first launched in the 1970s. SMC lenses show very low flare, superb optical characteristics and an even colour balance from lens to lens.

So we have our new SLR, probably with the kit 18-55mm zoom, which is a creditable performer and probably the best of all the marque kit lenses. But where do we go next?

We will now look at the various types of SLR lenses available, look at some examples of what they can do, and see which ones we might need for our particular styles of photography.

With the advent of the K10D and later bodies the option for lenses with built-in focusing motors has arisen. This gives us faster and quieter AF performance while retaining the conventional AF system for older bodies.

The K10D, K20D and K200D also have weather sealing and the new SDM lenses are also weather sealed to match. We no longer have to run for cover when the rain starts and this is a tremendous advantage in our unpredictable weather conditions.

The 12-24mm zoom is a rectilinear lens and reproduces straight lines as straight lines. This makes it ideal for architectural shots.

The Crop Factor

The digital SLR sensor is smaller than the 35mm film frame and, as a consequence, uses only a reduced image circle. This is useful in that only the best part of a film-format lens image is used and as the outer area is left unused it creates an effect similar to zooming in on the central part of the image.

Newer digital lenses are mostly designed only to cover the reduced size of the sensor and this has resulted in more adventurous design specifications and more compact lenses.

The resulting crop factor is approximately 1.5x for the APS-C sized sensors in Pentax cameras. This means that a 50mm lens, although remaining 50mm in all respects, will give a field-of-view similar to what you would see if a 75mm lens was used on a 35mm film.

So this standard lens, when used on digital SLR camera, has a field-of-view similar to a short telephoto lens on a film camera.

By keeping the camera vertical the fisheye lens can be minimised.

The Standard Lens

A standard lens is considered to be one that shows a field-of-view similar to human vision. In film camera terms this would be 43mm, and only Pentax market a 43mm lens, as most standard lenses are 50mm or slightly longer. For the digital SLR with its APS-C format sensor, the standard is approximately 31mm.

The 18-55mm standard zoom covers from a wide-angle to a modest telephoto and is much more versatile for general purposes. It's fairly soft at wide apertures, perhaps just nice for portraits, but crisps up when stopped down to give a very creditable performance. It's possible to make superb A3 exhibition prints with this lightweight lens.

For those who do feel the need for a higher quality lens the 16-45mm fits the bill. It's sharper wide open and also gives better results stopped down, but the improvement will be best seen on large prints. In one sense, you will know if you need this lens, but don’t be seduced into buying it if you can already make critically sharp images with your 18-55mm. The constant f/4 aperture is a useful feature, especially when using studio flash.

The new 16-50mm promises state-of-the-art lens design, plus built-in focusing motor, weather sealing and waterproof lens coatings. The constant f/2.8 aperture means a bulky and heavy lens but for sheer quality it could be hard to beat.

The 50mm f/1.4 lens, equivalent in its field-of-view to 75mm on film, now makes an excellent fast moderate telephoto lens. This could be ideal for portraits, but it is very sharp and your model may not appreciate too much definition. For general purposes, the fixed focal length of the 40mm, 43mm or 50mm lenses may be restricting and a modest standard zoom may serve better. This will certainly be true for travel and holiday photography.

Superzooms such as the new 18-250mm could be the answer for those who wish to travel light and avoid lens changing. The optical performance is very good at the expense of bulk and limited maximum apertures. It will not match the ultimate quality of more modestly specified zooms, but it will be very good and for many photographers it could be ideal.

Strong lines and a wide-angle lens pull our eyes into this image. Very wide lenses need care in use and the easiest way to improve your abilities with them is practise.

Wide Angles

The 10-17mm is a unique optic that offers a fisheye view of the world at 10mm and gradually straightens up as it is zoomed towards 17mm. Although never rectilinear, where straight lines would be reproduced as straight lines, careful composition can effectively hide the fisheye effect to produce very wide landscapes. However, any tilt of the camera and the classic fisheye curves will be revealed. This is a superbly built lens that offers enormous creative potential, but it's not easy to master.

By contrast, the 14mm and 12-24mm lenses are rectilinear and are suitable for architecture and any applications that require correct drawing of the image. The 12-24mm is an especially fine lens that can be recommended for the most demanding requirements.

The three standard zooms also start their ranges in the wide angle area. The 16-45mm and 16-50mm both provide a very respectable 24mm-equivalent and match well the optical performance of the wider lenses in the range. The 18-55mm starts at a more modest 27mm-equivalent wide angle.

The critical advice for the use of wide-angles is to get in close and fill the frame with the subject. If we stand back and just put a wide-angle lens on our camera without moving forwards the results will invariably be disappointing. Foreground interest can help when in this situation, as can giving high priority to framing and scaling the image.

Landscapes taken with wide angles need good foregrounds to give scale, otherwise the details in the image will look too small and even mountains will look far away and insignificant. Although the appeal of wide-angles is strong, they should be used boldly to get the best from them.

Wide-angle lenses are often used for creative effects because of the apparent distortion of perspective. Perspective is governed totally by the distance to the subject, so simply standing in the same place and taking pictures with a standard lens and then a wide-angle will have no effect apart from giving a wider view and the wide-angle results may be disappointing.

It's only when we move in to fill the frame with the subject that we exploit a change in perspective and the wide-angle becomes a powerful creative tool.

Landscapes, architecture and travel are the main uses of wide-angles, but don't be afraid to try portraits as well. Experimentation costs nothing with digital cameras.

Wide-angles are ideal for architecture, landscapes and travel but they need good foregrounds to supply interest. In this garden the urn stops the foreground from looking too empty. It also gives depth and scale to the image.

Hyperfocal Distance

Understanding hyperfocal distance is another critical skill for landscape photography. We'll explain this by referring to a prime lens (a lens having a single focal length) with a depth-of-field scale.

Taking the SMC Pentax-A 50mm f/1.7 lens as a typical example, if we set the lens at f/16 we can read off the depth-of-field on the lens (see illustration below). If we were to focus on infinity the depth-of-field marks show that the image should be sharp from around 15 feet away to a point far beyond infinity.

However, there's nothing further away than infinity, so depth-of-field beyond that point is wasted. If we turn the focusing ring until infinity aligns with the other f/11 point on the scale we see that our area of sharp focus now extends from infinity all the way back to approximately 8 feet.

We are now focused on a point 15 feet away. The image in the viewfinder won't look as sharp, but when the picture is taken and the lens stops down we will have maximised our depth-of-field. We have focused on the hyperfocal distance.

Most modern lenses do not have depth-of-field scales, so we can use a rule of thumb. This rule is simply to set a small aperture such as f/11, f/16 or even f/22 and then focus one third of the way in to the scene. This will be near enough to the hyperfocal distance and will ensure maximum depth-of-field.

If necessary, use a tripod, especially when the resulting shutter speed becomes too slow to hand-hold the camera. An alternative technique is to increase the ISO setting, which will enable higher shutter speeds, or to take advantage of built-in shake reduction.

A final caveat is to avoid very small apertures such as f/22 where possible because diffraction effects take the edge off sharpness. All lenses perform best at the middle apertures.

Top: Lens focused on infinity and DOF extends down to 15ft. Bottom: Lens focused on the hyperfocal distance, around 15ft and DOF of 8ft-infinity.

Telephoto Lenses

Telephoto lenses bring things closer and appear to compress the perspective. As before, perspective is actually dependent only on our distance from the subject, so it is the act of moving back to let the subject fill the frame that causes the apparent effect.

Telephotos compress distance and isolate details. Mountains will look more dramatic and faces can be isolated against blurred backgrounds. Some photography, such as sports and nature, would be virtually impossible without telephoto lenses.

This is where the small sensor of digital cameras becomes a real advantage. The 1.5x crop factor makes wide angle lenses more difficult to produce, but actually maximises our telephotos and brings real long distance photography within our reach.

As an example, a 300mm lens becomes a 35mm-equivalent 450mm lens, which is an enormous amount of magnification. As it may also focus down to as little as 1.4 metres then it also becomes a very useful semi-macro lens for the photography of small flowers and animals at closer range.

Often telephotos are used to isolate details and wide apertures will help to do this. Focusing on the eyes in a portrait and using a wide aperture will concentrate the viewer’s attention and ensure the background is suitably blurred.

Macro Lenses

Macro lenses are designed to focus very closely and are optimised accordingly. Strictly speaking, a proper macro lens will focus to a magnification of 1:1. This means that an object 1cm long will be actually 1cm long on the film, sensor and in life size. When enlarged and printed it will of course be much bigger than that.

Older macro lenses may only focus to 1:2 magnification, so our 1cm object will be recorded 0.5cm long, half life size. The closest focusing zooms usually focus down to around 1:4, quarter life size.

However, zooms will invariably have a curved field at this sort of magnification, so when photographing a flat subject the centre may be in focus but the edges not, or vice versa. Macro lenses will have a flat field and will be very superior in performance for close up work.

Having said that, there is no doubt that modern zooms that focus close are still very useful in the field for detailed shots of flowers and other small subjects. Long telephoto lenses such as the 75-300mm also focus close enough to make excellent studies of small flowers and wildlife whilst keeping some distance away. A 300mm focal length at six feet away gives a high degree of magnification.


Camera shake is the enemy of both close up and telephoto photography. The answer is a sturdy tripod. Flimsy plastic tripods will not be effective so the emphasis is on sturdy. This unfortunately also means inconvenient to carry and I am as guilty as anyone for leaving the tripod in the car.

For macro and close-up work I do believe though that a tripod becomes essential. Long telephoto work also needs the same sturdy support.

However, without a tripod there are some other techniques that may help. A monopod is a possibility for landscape photographers, although I find the image still wavers quite a bit.

Other supports include tops of walls, leaning on walls and posts and using the elbows to make ourselves more stable. A bean bag is an excellent support to use on a solid wall or stationary car.

Increasing the ISO is a powerful technique new to digital photography. With film we were stuck with whatever speed the film was, but with the digital SLR we can select a higher ISO when needed and take advantage of the higher shutter speed that results.

High speeds mean less shake, but also wider lens apertures, so if we can sacrifice some depth-of-field then using wider aperture lenses can also help in low light. The 50mm f/1.4 lens is a good example of a wide aperture lens. There is a trade off though so increasing the ISO is very useful if we need higher speeds but still want to use smaller apertures.

It is much better to have a grainy shot that is sharp than a fine grain shot that is blurred.

Shake reduction on the K10D and K20D is our latest tool and this will improve our ability to hold the camera steady by up to four stops. It's still necessary to take more than one shot to make sure.

Finally, hold the camera securely. Place your left hand under the lens and release the shutter gently. Stabbing at the shutter release will induce shake. If the camera is supported then using the 2 second delay release function to raise the mirror before releasing the shutter and there will be virtually no vibration.

So, regardless of the conditions there are no barriers to stop us getting out and about with our cameras. Pentax have always created brilliant cameras and without a doubt they now have the lenses to match.

Members photos with related tags: Lenses

Posted 20/01/2013 - 13:23 Link
Well done John, that's quite a piece of work
“We must avoid however, snapping away, shooting quickly and without thought, overloading ourselves with unnecessary images that clutter our memory and diminish the clarity of the whole.” - Henri Cartier-Bresson -
Posted 22/01/2013 - 12:36 Link
Can I just clarify one thing in the section about Hyperfocal Distance. You say set the lens to f/16 but in the next paragraph you talk about aligning to f/11. Should that be f/16.

I ask as one who has never been able to grasp Hyperfocal Distance from other explanations/calculations
Posted 23/01/2013 - 16:47 Link
Thanks Ken.

Barrie, the image also shows an example with a lens set to f/16 as it happens and in the context of this example the second reference to f/11 looks like a typo. Normally for maximum DOF and using the hyperfocal distance rule-of-thumb I would use f/16, being the smallest aperture before lens performance dips significantly.
Best regards, John
Posted 23/01/2013 - 20:16 Link
Thanks John, it's one of the easiest explanations on Hyperfocal Distance that I have come across, and did not want to mess it up.

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