Autofocus: ratio of good to OOF

Pindy

I'm curious for those of you who shoot more than I do and are more experienced (that's most of you):

1. How often do you find your AF nails it versus being
A) WAY off (more than a foot away from a subject, and...
a little off, but off enough to be considered a failure?

Now ask yourself the same questions and factor in a telephoto lens. Does your answer change? I have a feeling I'm having a telephoto learning curve issue.

A few more queries:

2. How much does technique fix these problems? (I am aware of the focus-and-recompose problem, at least)

3. How often do you buy a lens that has focus issues?

4. Aside from low contrast, what's the biggest foil of autofocusing and what do you do about it?

It seems like some days, particularly in the mornings and on cloudy days, I'm getting about a 40-50% IF rate with my EF 70-200 f/4L IS and this is with or without IS on. If this sounds obvious, I AM indeed jacking up the ISO if needed. I am doing my best to keep shutter speed on or above to focal length for shake's sake. On brighter days, I have a much better rate of success. The funny thing is it's not so much that the lens has to hunt on these bad days, but rather it LOOKS as though it's nailing the subject then you look at them later and it's not great.

I suppose I need to better understand the visual differences of focus and shake to really make this determination. Perhaps a tripod test would be in order as well.

Thanks for your insight.

wxwax

The best way to help you would be for you to post out of focus pictures and tell us what your focus settings and exposure settings were for the shots. The problem could be any number of things. It's virtually never the lens, by the way.

Pindy

wxwax wrote:

It's virtually never the lens, by the way.

Yeah I suspect that. Okay will do, though I canned most of the worst ones. I'll get around to it tonight.

Thanks

Jeffro

Pindy wrote:

Yeah I suspect that. Okay will do, though I canned most of the worst ones. I'll get around to it tonight. Thanks

It could be the focusing mode you are using...one dot, as opposed to all the dots...but again that takes more info from you. Center dot is the best. One shot mode is better than AI Servo if you are shooting still subjcts. AI Servo tends to look for movement.

Pindy

A few links:

Not terrible but not great

Maybe I'm crazy, but I hate the way this looks

Even worse

This one is fuzzier

Also bad

Here I was focusing on the logo on the truck.

I'll look for some more that aren't mired in shadow.

wxwax

What are your shutter speeds and apertures on these?

How close was your lens to the toy truck?

Pindy

wxwax wrote:

What are your shutter speeds and apertures on these?

How close was your lens to the toy truck?

EXIF is available by clicking "more properties". Sorry, Smugmug is down and I had to go to Flickr. The first one was f/5.6 and 1/400 at 200mm and the same but 1/320 on the second bird pic. The truck was f/4 and 1/160 at 192mm. I cannot ascribe the softness to the fact it was wide open, especially not in the center. Not on that lens.

Image Stabilization was on for all.

I was probably 1.4 meters from the truck. The closest focusing distance is 1.2m. I intentionally stapped back until I got it and left myself a bit of a margin.

wxwax

On the second one, the autofocus appears to have grabbed the leaves surrounding the bird. The bird is awfully small in the frame, and also dark, so that's understandable.

I disagree with your assessment of the truck shot. Some portions of the truck are trying to be sharp: the edge on top of the door, the black mirror... and the wood in the bottom right corner. I don't know if you used a center focus point and recomposed, or what your focus setting was, but it looks like the combination of f4 and your closeness to the subject gave you very little leeway in getting the focus right. Bottom line, you were pushing everything to the limit: narrow depth of field, close to your subject, and relying heavily on IS because your shutter speed was way too low. You shouldn't be surprised the shot didn't come out perfectly.

In the first shot, some of the leaves seem to be sharp. The bird is acceptable but not great. Once again, it's tiny in the frame. And again, you haven't told us what focus setting you were on. It would appear that the autofocus grabbed the high contrast leaves instead of the tiny dark bird.

All in all, three very tough shots for accurate focusing.

Pindy

I suppose you're right; the bird shots are poorly lit and they are small in the frame (oh for a 400). Sorry I thought I posted my focus specs (always center AF point, one-shot) but that must have been on a previous draft that I never posted. As stated before, I don't focus-and-recompose.

So I think I've just learned something about the conditions in which a lens will focus properly. I think this is the answer I wanted all along (that it's ME). I just looked at the better daylight shots and they're all in focus, even distant helicopters and aircraft as well as close, abstract shapes on the ugly industrial roof upon which I was shooting, such as HVAC units, ducts, lattices, etc.

Another thing that strikes me is how ugly the light can be—which I think has more of an effect on my liking or hating the photo than any other factor. You begin to see why this can be an art form and not every shot is magic, even for the seriously talented.

Thanks again.

wxwax

Light's huuuuuge!

claudermilk

wxwax wrote:

Light's huuuuuge!

Yup, remember it's ALL about the light. Think about the name of our hobby/profession/addiction. http://en.wikipedia.org/wiki/Photography

Pindy

claudermilk wrote:

Yup, remember it's ALL about the light. Think about the name of our hobby/profession/addiction. http://en.wikipedia.org/wiki/Photography

I come from the film music world and although I look at moving pictures all day, my sense acuity lies mostly in the ears. This is a real education.