Autofocus question

[J. Cobble]

Does everyone use the auto focus on the long lenses? I have a 100-400 l is and I find myself not using the auto focus at all. The problem is that when I use it and blow it up it is slightly out of focus. I get much better results out of manual focus. I do think it works because it does hit every one of five shots. It really starts getting bad at 400. Anyone have the same experience?

[IanD]

Nope, no problem here and I shoot mine racked out at 400 most of the time. Got to get me a 400 prime one day.

[Scottes]

Nope, no problem here and I shoot mine racked out at 400 most of the time. Got to get me a 400 prime one day.

I use mine set at 400 almost all the time. Depending on the subject AF is perfect. Other times I find it is because I focused on the wrong spot (ie; wing instead of eye), or that it's just about impossible to AF on something as small as the eye.

[Jim_T]

I use autofocus on my 100-400 99% of the time... I find it very accurate. The small viewfinder of the 10D makes manual focusing any lens a bit difficult..

[ssim]

I have seldom used my 100-400 on manual. I find it to be pretty much bang on for the autofoucs.

How big are you going with your enlargement afterwards. Are you doing any sharpening before you have it printed?

[KennyG]

No, don't have a problem with the 100-400L and AF, even at full 400mm with my 10D or 1D. What camera and do you have this problem with other lenses?

[J. Cobble]

drebel. let me try some more stuff. Maybe I am too picky :lol:

[Scottes]

I know the AF square on the 10D - and I'll have to assume the DRebel - doesn't really match the *real* AF area. If you have two distances within or close to the same square the camera may not be choosing what you want. It causes me a heck of a time on close-ups small birds - I "focus" on the eye and get the shoulder.

If you check the AF aim it at distinct objects with a large aperture. Distinct so the camera doesn't get confused, large aperture so you get a small DoF to more accurately guage AF.

[IanD]

I know the AF square on the 10D - and I'll have to assume the DRebel - doesn't really match the *real* AF area. If you have two distances within or close to the same square the camera may not be choosing what you want. It causes me a heck of a time on close-ups small birds - I "focus" on the eye and get the shoulder.

If you check the AF aim it at distinct objects with a large aperture. Distinct so the camera doesn't get confused, large aperture so you get a small DoF to more accurately guage AF.
I recall reading somewhere that the centre focus "square" is not in the centre but rather left top. I have always used the left top corner as my focus point (using the centre AF point) and have always had dead on AF.
Was I dreaming? Anyone else remember reading/seeing this?

[scottbergerphoto]

I know the AF square on the 10D - and I'll have to assume the DRebel - doesn't really match the *real* AF area. If you have two distances within or close to the same square the camera may not be choosing what you want. It causes me a heck of a time on close-ups small birds - I "focus" on the eye and get the shoulder.

If you check the AF aim it at distinct objects with a large aperture. Distinct so the camera doesn't get confused, large aperture so you get a small DoF to more accurately guage AF.
I recall reading somewhere that the centre focus "square" is not in the centre but rather left top. I have always used the left top corner as my focus point (using the centre AF point) and have always had dead on AF.
Was I dreaming? Anyone else remember reading/seeing this?
After how many Molson Golden's? (Just checked the Short Course and the Canon manual. No mention of center being on the left top.) :wink:

[Belmondo]

I recall reading somewhere that the centre focus "square" is not in the centre but rather left top. I have always used the left top corner as my focus point (using the centre AF point) and have always had dead on AF.
Was I dreaming? Anyone else remember reading/seeing this?

Repeat after me:
The center square goes on the front of the duck.
The center square goes on the front of the duck.

[IanD]

I know the AF square on the 10D - and I'll have to assume the DRebel - doesn't really match the *real* AF area. If you have two distances within or close to the same square the camera may not be choosing what you want. It causes me a heck of a time on close-ups small birds - I "focus" on the eye and get the shoulder.

If you check the AF aim it at distinct objects with a large aperture. Distinct so the camera doesn't get confused, large aperture so you get a small DoF to more accurately guage AF.
I recall reading somewhere that the centre focus "square" is not in the centre but rather left top. I have always used the left top corner as my focus point (using the centre AF point) and have always had dead on AF.
Was I dreaming? Anyone else remember reading/seeing this?
After how many Molson Golden's? (Just checked the Short Course and the Canon manual. No mention of center being on the left top.) :wink:
I found it :!:
http://www.popularphotography.com/article.asp?section_id=2&article_id=750
Pop Photo test report. Measured AF Sensitivity. Check out the article, page 3 I believe. If the same pattern holds true for the 10D could this explain some of the so called "front/back focus" measurebators love to rant about :?: :?:

[IanD]

I recall reading somewhere that the centre focus "square" is not in the centre but rather left top. I have always used the left top corner as my focus point (using the centre AF point) and have always had dead on AF.
Was I dreaming? Anyone else remember reading/seeing this?

Repeat after me:
The center square goes on the front of the duck.
The center square goes on the front of the duck.
Pointy end of the duck towards camera
Pointy end of the duck towards camera.
OK I've got it now :lol: :lol:

[Belmondo]

Pointy end of the duck towards camera
Pointy end of the duck towards camera.
OK I've got it now :lol: :lol:

So, what's your point?

[IanD]

Pointy end of the duck towards camera
Pointy end of the duck towards camera.
OK I've got it now :lol: :lol:

So, what's your point?
Exactly.

[IanD]

No comments on the AF chart?

[Cadwell]

No comments on the AF chart?

It's an interesting article. I wonder if the location of the actual AF point in the top left of the AF square is a general rule or whether the focus screen was just misaligned slightly in the unit they tested....

[Scottes]

No comments on the AF chart?

It's an interesting article. I wonder if the location of the actual AF point in the top left of the AF square is a general rule or whether the focus screen was just misaligned slightly in the unit they tested....

I would think that every one is slightly different.

Time to set up a black stick against a white background and do some testing.


Is it measurbating if you're just testing AF? If so, can you still go blind?

[scottbergerphoto]

I tested my 10D with the 50mm f/1.4 if you recall and posted it at: http://www.pbase.com/scottbergerphoto/50mm_f_14__focus_test
The Center Focus Point is the Center Focus Point on my 10D. I can't believe that Canon would intentionally make an off center/lateral point the center focus point. It also wouldn't explain why switching from using all the focus points to the center one resolves alot of people's problems with AF.
PS: I looked at the article you linked, and now realize that what you were trying to say, which I so stupidly failed to comprehend, is that the center of the center AF point is not in the center of the AF point. Since the actual area of the sensor is larger then the delineated box in the viewfinder, it's hard to know how off it might be in a given camera, and whether or not that makes any difference when dof is taken into account.
Regards,
Scott