Tuesday, August 14, 2012

A Fixed Focal Guide

This is for nuts like me who prefer fixed focal length (prime) lenses to the zoom lenses that usually come with SLR cameras. This is meant to be a guide as to how best to use each individual focal length, and also to make a comparison between using them on film or full-frame digital, versus APS-C sensor DSLR's.

First though, I'll provide some brief background as to why prime lenses are preferred in the first place. It is always agreed that zoom lenses are more convenient in getting a picture composed, and I actually use my zooms just as much as my primes - I'd say it's pretty much 50/50. I know that I'm not the only "nut" out there who feels this way - camera makers are still making prime lenses of all kinds of different types (like Stabilized, Macro - Optimized, etc.) and they're selling like hotcakes. I think, and most would agree that once photographers get on the learning curve, they realize a couple of things about lenses.

First, zoom lenses always have compromises in their design, however good they might be. One compromise is size and weight, especially when a zoom is very good. For new high quality zooms that really hold their own in image quality, the price that is paid is always size (and price!). Also, there are some new zooms that are using new manufacturing technology to extend the zoom range and reduce the size all at the same time, known as "all-in-one" or "travel zooms". These are quite good, but if you want ultimate image quality, this type of lens makes it's compromises in the image quality department, but are smaller, lighter and much more convenient.

The second thing a photographer realizes is that zoom lenses create compromises in one's actual photography. Zoom lenses, with their wonderful convenience of being able to vary the focal length with respect to where you're standing, make it so that we do not think that it might be better to change where we're standing. A shooting position from one particular focal length might not necessarily be the best position to be in for another - and when you're using a zoom and have not yet learned this lesson, you will succumb to simply turning the zoom ring instead of changing your perspective. I know that's what I do. It is generally agreed that prime lenses make for more creative photography, for the very simple reason that one must be more creative to use them.

Prime Lenses offer focal lengths which are designed with simple "objectives" in mind. These are thought of in four categories - Wide Angle, Normal View, Portrait and Telephoto. With respect for the way lenses were marketed during the "Spotmatic" film era, these are represented as 35mm, 50mm, 85mm and 135mm respectively, as the most common lenses available for 35mm SLR and Rangefinder Film Cameras. Lenses that were sold significantly different than these common focal lengths were described as "super" or "ultra" wide / telephoto.

Normal View (nominally 50mm but were sold by various makes at between 45 and 60mm) is thought of as the field of view normally seen by the human eye. As a lens, it was usually the one that came with your SLR camera in the old days, as they were the easiest and therefore cheapest optic formula to make. It is "the right" lens with which to approximate human vision, and so very common. My experience shooting at 50mm is that it's great for snapshot type photography, where a family member or small group of friends might be the main subject, with part of a building, or a scenic landscape in the background. A common restriction of 50mm is that you could never use it to fit in an entire building as a main subject, which is correct, because human vision cannot take in an entire building, unless standing so far away from it as to lose a lot of detail. Another observation is that it is hard to invoke "drama" in the shot, as this focal length does not provide any wide angle, or telephoto distortion - it simply sees the world as we do. However, 50mm is a great lens for creating great "bokeh" (nicely blurred backgrounds) because they have a very wide aperture, typically f2, f1.8 or even f1.4. This is because 50mm is the easiest optical formula to achieve. Such wide apertures also make them great for shooting in the dark without flash.

Next there is the Wide Angle lens. As the name suggests, these will take in a field of view that is wider than the normal human field of vision, and in doing so, will make things look farther away than they really are - just like the passenger side wing mirror on your car. Wide angles are becoming the preferred lens to have by many, because they can be used to capture a whole building, a wider landscape, a larger group of people, great interior shots, and an added sense of drama, because of the introduction of some wide angle distortion. Many feel that if they could only have one lens, it would be wide. To take a shot of a single person or small group with a wide angle, you have to step closer to them, but the beauty is that you can get a more exciting looking picture as you balance the main subject while playing the wide distortion around them.

Portrait lenses have a tighter than normal field of view, intended for shooting a head to shoulder picture of a single person or small group, with a very de-emphasized background. These are also typically very fast (wide aperture, great bokeh) lenses, but are bigger and heavier than normal view lenses. There is no noticeable distortion characteristic, but a true Portrait Lens should feature a bit of "soft focus" to best make a flattering portrait with a nice glow, and subtle tones in place of lines and skin blemishes.

Then there is the Telephoto. These are long focal length lenses - greater than 100mm. These are useful in situations where you simply cannot get up close to the subject, as in sporting events, or music concerts. A good telephoto will bring a subject in very close and very clear, but also adds telephoto distortion, which is a compression of distance. It is hard to make "artistic use" of this kind of distortion, unless there is a long repeating pattern in the depth of the picture, as I discussed here. I am also of the opinion that telephoto is the best use of zoom (in other words, you might as well have a Telephoto Zoom) as you are not likely to gain much of anything by changing your vantage point if you are already at a "telephoto distance" from the subject.

Finally, the "crop factor" difference between a full frame 35mm camera, and one with an APS-C sized Digital Sensor makes a huge difference in the actual lens selection. The APS-C Sensor is just like adding 1.5x (Nikon and Pentax) or 1.6x (Canon) of "digital zoom" which is great if you like to shoot from a greater distance, and not be right in the face of your subject. On the other hand, if you are a radical wide shooter, with APS-C cameras, it is more difficult to achieve super-wide, unless you buy a new purpose built APS-C lens. It's enough to change the entire purpose of a lens - a Full Frame Wide Angle becomes your new Normal View lens, and a Normal View will become a Portrait Lens, as the following table will show:



Full Frame / 35mm Film
APS – C DSLR (1.6x Canon)
20mm
Ultra Wide Angle
32mm Bold Wide Angle
24mm
Super Wide Angle
38.4mm Normal Wide Angle
28mm
Bold Wide Angle
44.8mm Wide Normal View
35mm
Normal Wide Angle
56mm Normal View
50mm
Normal View
80mm Portrait
85mm
Portrait
136mm Telephoto
100mm
Moderate Telephoto
160mm Telephoto
135mm
Telephoto
216mm Super Telephoto
200mm
Super Telephoto
320mm Ultra Telephoto

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