Friday, March 15, 2013

Zoom Lens vs the 50mm Prime Lens

Note: All photos on this post were taken with the Pentax K100DS and the Vivitar 50mm 1.7 Prime lens (made by Cosina from the late 80s or early 90s). Click on the photos to view them full size



There’s always that excitement when you’ve purchased your first DSLR that came with the kit lens of 18-55mm. The photos are much better right out of the box than the standard point and shoot cameras. Photos are clearer and sharper and offer more realistic colour rendering.

But after a while, there’s that creeping need for even better photos. After all, a well composed photo tells a story. And photography is all about composing a theme in two dimensions to tell your story. Based on you interests, you could opt for a specialized lens. But specialized lenses cost way more. Action photography, bird watching, nature shoots need a good telephoto lens which are expensive. But for the regular daily walkaround photography, there is much simpler option.

This is where the 50mm prime scores. How many times have you accidentally taken a stunning photo where everything just came together in perfection? I know I always go back to looking at those photos with pride. A prime lens makes this consistently possible. It has only one focal length which seems to be a limitation as one cannot close in on the subject or expand the area of focus. But the important thing to note here is that 50mm offers a field of vision that is very close to the human eye’s range. The prime ends up capturing almost exactly what we see with our visual range in a setting. This makes it more pleasing and natural.

The next logical argument would be that the kit lens offers a setting at the same 50mm. All that one needs to do is to set the focal length at 50mm and shoot. The crucial difference is that the quality of the image takes a beating with the kit lens. To make a zoom lens, there are many components required to work in tandem. As the cost of the lens has to be viable, there is a compromise made. Otherwise all lenses should take equally good photos. The complexity added in zoom lenses means the glass or plastic used in the lenses is of a slightly lesser optical grade. Those who wear spectacles know what I am talking about when I say optical grade.

Some of the major advantages of a prime are:

Forced Learning

A prime lens usually offers the ability to manually change the aperture over a wider range than kit lenses. And if the lens is a manual focus lens (as most of the older ones are), then there is a learning curve involved. Patience is required to get that right shot. It took me around a month to understand the various combinations of aperture, shutter speed and ISO for needs based on ambient parameters. For example, I learnt through trial and error that fast moving objects need a higher shutter speed (1/180 or more) and higher aperture (f2.8 or f2) to allow more light for a shorter span of time. The results were satisfying!




There are so many older prime lenses available that are very very economical. The lens used to capture all the photos in this post was purchased for  INR2,800 ($52). Though it is just an above average lens, the sharpness and clarity trumps more expensive kit lenses. Sure, one can always achieve the same output quality with a much more expensive lens. But what’s the point of that when you can pick up an old good one for a fraction of the rate. Once I learnt to focus properly, I got good photos that were near perfect at even 100% enlarged.



No Zoom, Better Composition

The lack of zoom is actually a motivation to workout better. If you need a close up of the subject, you have to move closer physically. I had to walk for a while and finally get down on my knees, bend forward and backward to get this little tribal girl’s photo. It would have been so much easier if I had a zoom lens. I could have sat in one place and just zoomed in and out till I got the portrait. But what I saw was that I had to intimately understand my subject if I wanted a good photo. This got me working in tandem with her to finally get the right expression.



Aperture Range

This is perhaps one of the most important advantages a prime lens has over kit lenses. Natural looking photos require no flash to be used. And low ambient light poses a challenge. Kit lenses have a maximum useable range of F3.5-5.6. This means photos in low light need to be taken with very low shutter speeds or a combination of low shutter speed and high ISO sensitivity. Low shutter speeds demand the need for a very steady hand. Below 1/10 it becomes harder to obtain a steady image. The other resort is to use a tripod or use the flash. Using a flash removes the attraction of a dim lighted scene.

A prime lens on the other hand can have a maximum aperture of f1.4. This allows the lens to allow in much more light and obtain sharper images with higher shutter speeds. This photo below was taken in a restaurant with very low yellow lighting. Achieving a reasonably sharp image of the glass became easy by setting the aperture at 1.7 and using a speed of 1/15; which would have been impossible with a kit lens with the camera being hand held.



Planar Depth of Field

At the widest aperture, the prime lens has the least depth. This means the lens only focuses on a very narrow plane of view. One can use this to keep only the subject in focus and blur the remaining foreground or background or both.  The narrow DOF allows for more creativity without the use of flash. There is much more to learn and training the camera to “see” what we see. It also forces us to learn to focus properly. The right photo makes is a wonderful result to see. There is more time to use natural light for those warm sunset sceneries.



Prime lenses made for film cameras were made to work with the 35mm rolls. The sensors of the new age digital SLRs have a cropped sensor usually with a 1.5 ratio. That means an old 50mm prime used on a digital SLR is actually similar to a cropped telephoto. For example on the K100DS, the multiplier is 1.5 which means an SLR 50mm works like a 50 x 1.5 = 75 mm. This does not pose any problems as a focal length of 75 mm makes for great portraits as seen above. All other functionality remains the same.

So have fun shooting and if possible, experiment with primes. I do use my kit lens for most occasions. The manual focus prime is harder to manage but boy does it give me some satisfaction. Auto focus primes are a must have if one can afford it.