more serious post - help with focus 2 pics

[martcol]

I was out just playin' with my new 100-400 lens. Evening (after work) so reasonable light. Hand-held first attempts with the longes lens I've ever had. Took this shot of two pigeons (sorry no ducks!) and notice that the bird at the back is in focus Whilst the one in front is badly off but the focus point was dead on it. So, I think I've got the dreaded back focus problem.

http://images.fotopic.net/?id=4321444

Crop


http://images.fotopic.net/?id=4322060


So this morning I go out and take more shots, on a sturdy tripod reasonable light and it seems spot on. Fucus point in centre of part of frame marked. Questions will come later.....

http://images.fotopic.net/?id=4321443

Crop


http://images.fotopic.net/?id=4322059

I don't want to do no ruler test. It makes me feel too geeky (:oops:) and I just don't have the patience. I tried once before with a 50mm lens and it took me all day and I still wasn't any clearer.

The pigeon shot freaked me. The bench shot made me happy. So question: If my 10D isn't back-focussing what happened? It isn't camera shake 'cos some areas are lovely and sharp (pigeon shot).


By the way Pigeon shot: ISO 200, F5.6 1/250 Focal Lenght 330 mm
Evaluative Metering

Bench Shot: ISO 200, f5.6, 1/100 Focal Length 400mm

Shot in RAW a little sharpening and exposure compensation in C1.

Oh, and I was roughly the same distance away from the subject both times.

Thanks

Martin

[scottbergerphoto]

The 10D focus issue can be very frustrating. Sometimes focus is dead on and other times it seems off. Have you tried manualy focusing and seeing where the Focus Light comes on? It seems that whenever I do that MF and AF are the same. I was about to send my 10D in for calibration, till I took a series of shots with the 50 f/1.4 and they were dead on. My 70-200 f/2.8 is going in to be checked. I guess the only way to know is to do one of the focus tests with all your lenses.
Good Luck,
Scott

[sp00g3]

The 10D focus issue can be very frustrating. Sometimes focus is dead on and other times it seems off. Have you tried manualy focusing and seeing where the Focus Light comes on? It seems that whenever I do that MF and AF are the same. I was about to send my 10D in for calibration, till I took a series of shots with the 50 f/1.4 and they were dead on. My 70-200 f/2.8 is going in to be checked. I guess the only way to know is to do one of the focus tests with all your lenses.
Good Luck,
Scott

umm.. Were you completely zoomed in at 400mm? Reason I ask even at f5.6 DOF is very shallow at 200 - 400 mm. Why don't you try increasing the f to 8 where the lense will be at its sharpest? Dont forget the DOF preview...

[robertwgross]

When your lens is heading in the direction of "wide open", then DOF gets very critical, and DOF preview becomes much more important. If the target area of focus has worse contrast than some place just outside of the target, then that makes it harder for the contrast sensor function of autofocus to work. In other words, if you shoot at a pattern of black and white lines, the focus should be more accurate to judge as compared to a blob of dark gray and light gray lines. That is what makes the ruler test good.

Some of you have seen a digital exposure target. It has areas of black, gray, and white, and you use that to check out your histogram spikes. Well, it also has a lot of contrast, so it makes a good autofocus target as well.

Of course, I am too cheap to buy such a target, but I made my own. I took a small piece of white foam board for white. Then I had some 18% gray tape that I made a horizontal stripe with. Then I had some total black tape that I made a vertical stripe with. I use that for exposure checks and also for autofocus checks.

---Bob Gross---

[Haifidelity]

Your 10D Focussed accurately, just not where you intended it too. I don't think my 10D has any focussing problems, but I do believe it can focus on objects that I don't intend to be in focus. With a smaller than full frame viewfinder, it's hard to tell what's in focus sometimes.

I wouldn't sweat it. If this was consistently doing this, I would worry.

-hza

[maderito]

How are you sure that the 10D selected the center focus point on the pigeon image?

There is very little contrast on the bodies of the pigeons. It's quite possible that the 10D right-of-center focus point was automatically selected -- possibly in the wing feathers of the bird on the right where there is more contrast. (As you probably know, AF relies on image contrast.)

Ducks are probably more predictable. :) :)

[GenEOS]

Ditto...You need to be at f8 or higher to bring both those birds into focus. At f5.6 your dof is short. The closer you are to the subject, the worse it will be...or better, depending on what you are trying to achieve...

[Jim_T]

Yep.. I'll throw in another vote for DOF.. f/5.6 may not be an incredibly fast f stop, but at 400mm you wind up with a very shallow depth of field..

When using my 100-400, I usually make sure the camera is in Av mode and force the lens to higher f/stops.. (As others have mentioned.. Around f/8 )

Another thing to watch out for is motion blur.. Setting the stop to f/8 might drop your shutter speed to 1/125th or slower.. At that speed, perky little birds and other fast moving targets won't come out sharp. In this case, you'll have to use a higher ISO..

Who said photography was easy :-) :-)