Focal Lengths compared
As shown in the previous post, the focal length has a big impact on how your picture looks like. The two standard exercises that anybody with a zoom lens (or a bag full of prime lenses, if you're into that) should do are:
- Make pictures of the same object, at the same apparent size, with various focal lengths. That is exactly what was done in zoom in... zoom out....
- Make pictures of the same object, at the same distance, with various focal lengths. That is the subject of today's post.
Clearly a wide angle shot! My lens doesn't go any wider than 18mm, but that is still pretty pretty pretty pretty wide. Details are hard to see, but boy do we get a lot of the environment!
A slightly tighter crop at 24mm. This is still a very wide angle - lot's of surroundings, and a very tiny subject.Notice how details that were visible at the edges of the previous picture have disappeared (the branches at the top and at the left for instance).
Do not make the mistake of saying "we are getting closer" - we're not. But the focal length is now 35mm, so we've zoomed in on the subject.On an APS-sized sensor SLR, the 35mm lens is usual referred to as the "normal" lens - roughly equivalent to how we see the world with our own eyes.
The 50mm lens is the "normal" lens for 35mm film, or for "Full Frame" DSLR cameras. On an APS-sized sensor the focal length is -although a speck too wide- reasonable useful for portraits.It helps of course that a decent quality, razor sharp 50mm/1.8 AF lens usually can be bought new for around $100!
80mm - by now, al surroundings have gone and only the subject remains. This focal length is the beginning of the "portrait" lenses. A focal length of around 85mm is wide enough to get someone's head without having to stay away a long distance, but the "tele lens effect" shortens distances enough to make noses and chins look smaller (or at least not emphasize their size).
Most camera manufacturers will sell pretty fast 85mm lenses - the wide aperture will help to "knock out" the background.
The "far end" of the portrait range is 135mm. Even from a good distance, the subject is bigger than the entire frame. It is possible to find 135 f/2 lenses - beyond that focal length super fast lenses (even primes) get rare. And for a reason - at those apertures and focal lengths, the depth of field gets really, really shallow.
Only detail is left at 200mm, and not a lot else. This picture shows another problem with long-focal length lenses - it is not sharp. That is not a problem of the lens - the Nikkor 80-200ED that was used is razor sharp - but operator error. I was in a rush and forgot to check the shutter speed - and the used 1/60" is too slow for a lens like this!
Everything in the picture gets greatly amplified at this focal length, and that inludes minute hand shake. The rule of thumb is to use at least a shutter speed that is the inverse of the focal length or faster - I should have used at least 1/200" for this image.
I didn't, and the result is an unsharp image. But, nothing is ever a complete failure: it can always serve as a bad example.
Remember, one focal length is not better than the other - it all depends on what the image is that we're trying to create. Beginners usually look for telezooms that have a focal length as large as possible - 300mm, or even 400mm, and manufacturers are more than happy to sell those lenses.
But longer doesn't always mean better. The ability to take sharp pictures of birds is great, but completely useless when trying to take pictures of the family barbecue. Make sure you have the entire range covered, preferably by two or three lenses.
