DOF at long ranges ??

Had my first chance to shoot with my recently acquired 70-200L f4 the other day. I never really shot sports before so I have yet another learning curve to master.

My 6 year old son was playing T-ball and I was trying to get him in action. I was kneeling on the first base side right up against the dugout fence shooting all the way across the mound to his position at third base.

I noticed that when trying to shoot wide open at f/4 and 200mm (on my 40D), I kept getting fuzzy halos around him and the shot was not in focus at all.

In fact I took four shots in a very short period of time. At 70mm he came out fine, at 106mm it was acceptable but a little fuzzy, at 160mm it was bad, and at 200mm it was like looking into a foggy mirror.

It was only when I started stopping down to f/8 and f/13 did those long distance shots start to look good.

So is it my lens? Or can you not (in general) shoot far away subjects at wide open apertures?

You should be able to nail the focus with that lens at 200mm if the light is right. What was your shutter speed? You'll need faster shutter speeds at the longer focal lengths to be sure.

Make sure your camera is set to servo focus and take multiple shots with the highest speed continuous FPS your camera allows.

Examples of what you're talking about might be helpful too.

How far away were you? I have no problems shooting my f/4 IS @ 200mm. It's probably my sharpest lens. Can you upload some of the bad (and good) pictures? Something sounds amiss.

In general... As the camera to subject distance increases, so does your depth of field.

Probably nothing wrong with your lens... you just missed the focus.

You don't really have to worry about DoF. There's always going to be OOF shots when using AI Servo. Remember that the camera can only guess where the focus will be, and it will get it wrong a number of times.

From the distance your talking about , i don't think it's a DOF problem . I shoot the same distance at f/4 @ 300mm and have no problems. Something else is going on here. Post some shots if you don't mind. Is this the only time , you've had this happen ?

Here are 4 shots all cropped roughly to the same size frame.

I checked the AF points of each shot in DPP. Every shot had an illuminated square on the center of my son's shirt.

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It's not a DOF problem. Something else is going on. Your shutter speeds are fast enough, unless you really had the shakes . It's not like he's moving much either, you could have used one shot for these . Are you using any type of filter ?
Have you used this lens for anything else ? If so, what where the results.
I'm really thinking maybe you wasn't all that steady when you pushed the shutter.

That looks really wrong. It might be the lens. You should test on a tripod using manual focusing in liveview as a baseline. That way you rule out something wrong with the optics. Once there you can see if something funny with your AF.

Would also helps if you have a friend with a canon body you can test on to rule out the camera as well.

I think that maybe the lens needs to be looked at by canon from your samples.

To me (for what it's worth), the background is showing camera shake.Notice the bleachers in the back ground-they are not blurred out the way they should be,they are showing a different blur-shake (it shows more at a longer distance).I would try a controlled test on a tripod (in good light) to see if there is another problem.The bleachers are not the way they should be even tho they are not the focal point,the blur is wrong.

coeng wrote in post #10193032
Here are 4 shots all cropped roughly to the same size frame.

I checked the AF points of each shot in DPP. Every shot had an illuminated square on the center of my son's shirt.

http://njitgrad.zenfol​io.com/img/v15/p146081​7-5.jpg
http://njitgrad.zenfol​io.com/img/v17/p212566​870-5.jpg
http://njitgrad.zenfol​io.com/img/v18/p287136​142-5.jpg
http://njitgrad.zenfol​io.com/img/v16/p387331​73-5.jpg

The most striking things are:
1. The smear was more pronounced in the longer-FL shots, and barely present in the 70mm shot. (However, if you look closely at the chain-link fence behind your son, you can still see a small amount.)
2. The background was affected more than your son.
3. The smear was asymmetrical -- normal out-of-focus blur should be symmetrical (e.g. highlights rendered as a circular blob).

CountryBoy wrote in post #10193189
It's not a DOF problem. Something else is going on. Your shutter speeds are fast enough, unless you really had the shakes

I agree it's not a DOF problem.

However, it's not a camera shake problem either -- one would expect the same angular amount of blur for both near and far objects if it is caused by camera/lens shake.

CountryBoy wrote in post #10193189
Are you using any type of filter ?

Filter is an interesting possibility, as a soft focus/blur filter will produce more "smear" around highlights/bright objects but barely affect darker objects.

However, it does not explain why the blur was asymmetrical in shape.

eddyav wrote in post #10193588
To me (for what it's worth), the background is showing camera shake.

As mentioned, it is NOT camera shake since your son was not affected (or at least not affected to the same angular amount).


My guess is that one of the internal element is loose and thus off-axis.

I agree you should either send it back to the vendor, or send the lens to Canon for inspection.


Sorry you are not getting the same jubilee most others get to experience when they "discover" what L lenses are all about for the first time. However, don't despair. This will only make the experience more intense when you get a properly working L lens.

Good luck.

All I used was a UV filter.

some cheapo uv filter? tristar optics maybe?

To rule out filter problems or camera shake, I would take a test shot using the same Tv and Av values at 200mm, but having removed the filter and with the camera on a tripod.

If no problem shows up, it would point to your technique; if the problem is still there you may have a problem with the camera or lens.

You could see easy using this:
Depth of Field Calculator (online)
that it isn't a problem of dof.
I think is most likely a problem of lens rather instead of cheap filter because in that case the problem will be visible even on the first shoot at the short focal range.