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Photography Question 
Ron Evans

f2.8 - Practical use?

I've spent the last 2 1/2 years learning as much as I can about the technical aspects but have zero formal training under my belt.

A big emphasis is always placed on "fast" lenses needed for indoor events. I personally find myself trying to NOT use 2.8 simply because such a shallow depth of field makes it too difficult to get the correct focus.

The only situation I've found this useful was inside the reptile house at the zoo when I wanted just the eye to be in focus on a snake. I guess this would be consider macro.

I'd say 9/10 times I try 2.8 I end up with the focal point being slightly "off" and don't like the fact that the critical part of my image isn't as sharp as I'd like. So...I'm just wondering what other practical application is there for using 2.8 or faster apertures? And, is it really worth the extra $$ for the lenses that carry these "fast" apertures?

I'm assuming the answer is "yes" and that at the end of the day it's still beneficial because stopping down from max aperture results in the sharpest image possible. Hence 4.0 on a 2.8 is crisp and I avoid the critical depth of field issue but I'd like to have some voice or educated reason to help me out here.


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6/23/2009 8:54:12 AM

Gregory LaGrange
BetterPhoto Member Since: 11/11/2003
  The motivation for making fast lenses is really only one practical application, and that is to let in more light. The result of that is you get a shallow depth of field, that you can use for mood creating.
I've wonder if you have two lenses of identical focal length, say 400mm. If one lens has a max aperture of f/5.6 and the other is f/2.8, if you shoot both at their own respective max aperture, would the depth of field be different. Or would they be similar since both lenses are at their max aperture.
Whether a faster lens is worth it to you depends on you, and depends on what you want to shoot. I can't see any lens maker thinking it would be good to come out with a short focal length lens that has a low max aperture. That's pointless because the focal length of a lens influences the max aperture it has. That's why a fast 400mm is so much bigger in physical size than a regular 400mm.
But there's nothing like the freedom of not feeling limited by a small max aperture.

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6/23/2009 2:51:20 PM

Bob Cammarata
BetterPhoto Member Since: 7/17/2003
  Faster lenses equate to faster allowable shutter speeds at lower ISO settings within a given amount of light...a must in wildlife and/or sports photography.

Those 2.8 prime telephotos (and 4.0 super-tele's) cost more but typically, they will have better glass and will be sharper and yield more accurate color reproduction.

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6/23/2009 3:18:49 PM

Alan N. Marcus   Hi Ron,

Consider that the SLR presents a pre-exposure view to the photographer. This view is present with the lens set to wide-open. Thus the SLR with a fast lens has the advantage; a brighter image allows the photographer to composes and focused more accurately. Being wide-open, the larger aperture delivers a shallow depth-of-field. Shallow depth-of-filed translates to more accurate focusing because when the lens is racked just a fraction of a millimeter forward of backwards, the image visually goes in and out of focus. Now that the lens is critically focused in the wide-open position, the SLR automatically stops down to the taking aperture. This act expands the depth-of-field zone. The bottom line is the larger aperture lens has advantages. The disadvantages are elevated cost, and likely sub-standard performance when actually called upon to image close to the wide-open positions.

Alan Marcus

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6/23/2009 4:11:14 PM

Ron Evans   Thank you all for taking a moment to respond.

Bob - your reply reads like a textbook and your comment regarding it's a must for wildlife and sports is really one of the primary reasons I ask the question.

I don't see 2.8 as being an acceptable aperture for shooting sports because I find that the focus point often times misses the mark resulting in most of the image being out of focus.

For example, you may get the basketball in focus but with such a shallow depth of field the player is the blurry.

I own a canon 70-200is 2.8 and a sigma 18-50 2.8. Both have produced excellent images with my 40d but I've also gotten very similar (if not identical) results from my e-500 paired with the kit lenses.

I honestly don't know if I've used 2.8 for more than 1% of my photos and I've shot a lot of animals and sports.

Perhaps I am not using an appropriate auto-focus setting or something else is not quite right.

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6/23/2009 4:27:21 PM

Gregory LaGrange
BetterPhoto Member Since: 11/11/2003
  If you hear people say that an f/2.8 lens is a must for wildlife is because of natural tendency of wildlife to be most active(hence more opportunities and easier for the photographer) during early morning and late evening. Lower light levels.
And for sports, how many times is that played at night, indoors, or when the duration of the game goes from good light to low light two hours later?
For your focus problems, that's something that can be overcome by just doing better at focusing. Whether you do it or you let the camera do it. It doesn't make f/2.8 unacceptable. In fact, f/2.8 is great for shooting it.
There isn't something inherent about a lens that's f/2.8 that is going to make it a sharp lens. It's just that in the real world, a lens company isn't going to make something like a 70-200 f/2.8, or a telephoto f/2.8, and not make the glass/optics really top shelf stuff.
So, like I said, it depends on you and what you want to shoot with it. If what you're doing with your e-500 is getting you what you want, then that's great. An f/2.8, or any other fast lens is a great thing to have, that some people use often wide open.

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6/23/2009 11:27:50 PM

Gregory LaGrange
BetterPhoto Member Since: 11/11/2003
  And also I want to add to what I said about shallow depth and mood creating. Purposely using a lens wide open for the shallow depth of field is common for sports for emphasizing someone against the background, or other people around them.
Saying it was for mood creating made it sound like you would only use f/2.8 for stuff like portraits.
And really, going from 2.8 to f/4 doesn't make that much difference in field depth. A couple of inches? If the ball is in focus and the player isn't, he's still out of focus at f/4.

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6/23/2009 11:42:51 PM

Bob Cammarata
BetterPhoto Member Since: 7/17/2003
  Red-headed Woodpecker
Red-headed Woodpecker

Nikkor 600 mm f-4, TC-301(2X) teleconverter

© Bob Cammarata
Nikon D300 Digital...

Another key point worth mentioning involves the use of teleconverters.
A 300 mm f-2.8 at 1/500 second without a 2X teleconverter becomes an 600 mm f-5.6 at 1/125 when the T/C is added.
This is still fast enough to freeze a bird in flight if the light is good.

Depth of field IS an issue wide open but with distant wildlife, you can still get acceptable detail of the whole animal by critically focusing on what's important.
As long as the eye is in focus, the rest of the scene can fall where it may.

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6/24/2009 1:56:30 AM

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