Educate me on AF

413x

413x

413x

Caporegime
Joined
13 Jan 2010
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I am recently struggling with AF

more often than not (far more often) pictures i take are not in focus. the focus indicator says it is in focus but sometimes the shot is completely out of focus.

some of these are hi speed shots and i am probably not very good at it. but others are static and still they are out.

my issue is i dont really know it is me/something im doing etc.

one lens..my 100mm IS 2.8 macro L gets far far more keepers than the rest. it is on the other end of the scale. I get more than i would expect.

all my other lenses are the opposite
this includes
sigma 120-300mm OS f2.8
canon 50mm f1.8
new sigma 35mm f1.4
somewhat canon 10-22mm f3.5-4.5 (although i havent used this in a while)

i just dont know if this is technique (likely), lens, conditions, me being too picky, 60Ds AF
if it wasnt for my 100mm macro L f2.8 iw ould be seriously concerned!

If anyone has any input id be grateful.
i kind of want someone else to use my gear and say its me because of X, Y, Z
i dont actually know anyone who i can physically do this with
 
I'd try a few shots indoors using a tripod, manual focus and a couple of the same subject using autofocus and compare. That would eliminate the camera. Also make sure the shutter speed is up above 1/50 or so in whatever mode you are using.

I generally set my camera old as it is to single point autofocus and just make sure the subject is under it.
 
If it can focus fine with liveview mode then it probably just needs a bit of microadjustment on the body to make it focus a bit further forward or back.

If the focus is off even in liveview then it could mean an issue with the body but seeing as you think it works fine with the 100mm then it would be rather odd!
 
i have given it a try tonight (not ideally enough light)

however.

so far the macro L is absolutely spot on. its DoF is so narrow the only thing that is in focus is the black line
and it is perfectly in focus
it may have a tiny tiny amount of backfocus. nothing i would worry about.
the line 2mm behind target is ever so slightly more in focus than the one 2mm nearer

the new sigma is definitely back focusing in both live view and viewfinder
 
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With the Sigmas that I've tried (18-35mm F1.8 and the 120-300mm F2.8 Sport) I've found the AF to be a little less reliable and certainly less accurate out of the box compared to Canon lenses. I guess that's to be expected to some degree since I doubt Canon are helping them make their lenses better lol.

AF testing can be a bit fiddly to setup and like you said, you need good light and a good target that provides sharp contrasts. The camera needs to be perpendicular to the flat target to give you the best chance of getting the target right etc and using AI Focus mode etc doesn't help so oneshot is normally recommended afaik.

You can make adjustments on the body but these are for focusing at any distance. If you want to tailor it more then you can get the Sigma USB dock and tailor your micro adjustments at a variety of distances. You can make it back focus more when close and less at a distance etc so it gives you more flexibility there. The drawback here is that the adjustments are on the lens so if you use it on another body then it will carry the settings across.
 
i think without a proper measure for 45 degrees you are right. and that lenscal seems to solve that by the looks of it
 
You also have to realize that a lens like the 120-300mm is not designed to work well at very short focal distances so you get some softness.


Anyway if you use liveview and get a focus error then there is something wrong with the lens most likely, but I wouldn't rule out technique. most people when they claim focus errors actually have a technique issue. Whenever you shoot with a shallow DoF (fats prime or long tele lens focusing up close) the technique needs to be perfect.
 
I'll definitely try the cereal box

High speed I accept it is my error. But how to improve I'm not sure. It's like the AF can't focus on the area it is on. I am well aware I am bad at panning but I don't actually know how to improve other than just trying more and more

But even static shots seem to be wildly out too much. This can't be a back/forward issue. There is no focal plane to be seen. The AF just seems to fail. I know the focal point needs contrast. Maybe this is part of the issue.
 
There should always be something in focus whether it be in front or behind of your target. If everything is soft then it could be a lens issue. I had this with my old 100-400mm where it was often soft with no part clearly in focus and it turned out to need servicing.

If you've got issues with multiple lenses and you can't see it front or back focusing then that seems a little odd! Time to get the camera on a tripod and do some liveview focusing on a good target in good light to see whether its definitely the case.
 
Might be technique but make sure your lenses can AF in live view, if they can't then there's a wider problem with the body or lenses. I rented an older 120-300 f2.8 and I think I got lucky because it was absolutely spot on.

I guess you're out of luck if you need MA, or it's a good excuse to upgrade to a 70D/7DII :p
 
ah definitely a reason for the 7/70d

If anything the sigma 35mm is a small 2mm out using the guide linked
The 100mm macro is near perfection (the dof is so small with that that the black target bar goes out of focus at the top/bottom compared to middle)
I have managed to get a 2mm flower stigma in focus hand held with that lens.

Just tried my long lens.
On the tripod it seems good. At the absolute minimum focus distance and focal length (120mm focal length) it's near spot on too.
It's dof is wider but the target is definitely in the sharp area. (and looks fairly sharp)
The width of the in focus area seems about 4mm (on the chart) and if anything it's slightly forward and definitely correctable in micro

So.. Its me I take it? Somehow I am just not getting the focus to lock to a moving target. Or is it the point I am trying to focus on hasn't sufficient contrast across the focal point? I don't know
 
The new sigma does seem pretty guilty at not focusing on correct spot both by hand and on tripod at different targets.
There are definitely times where the focus point is identified and agrees with what I see when the shutter closed yet the plane of focus is definitely behind this. If the focal plane is about as wide as the focal point the actual plane is about that width behind it.

If this is consistent that's fine as I'm guessing it can easily be corrected. There is after all no range.
 
Aye, I still need to have a proper sit down with my 18-35mm as it definitely likes to back focus when I'm at 35mm and F1.8 :/
 
its definitely noticeable. on mine

100mm L - spot on, at least now i know why i like this lens best)
10-22mm - undetermined
120-300mm - seems ok, more testing required
35mm - seems consistent error (at least consistent!) more testing

the 120-300mm has questions for me, but i think it is not so much back/forward but something with not being able to focus on the point i am trying for. be it lack of contrast, not fast enough, i dont know. To me this now seems as the camera not being fast enough +moving with the target compounded by my poor panning.

the 35mm is def not this, it is absolutely missing the focus point. but sometimes it produces pictures that completely miss. but this never happened in the tests. could it be that my focus point is on target but due to back focus its actually focusing on something 3 feet back?
 
al4x said:
its definitely noticeable. on mine

100mm L - spot on, at least now i know why i like this lens best)
10-22mm - undetermined
120-300mm - seems ok, more testing required
35mm - seems consistent error (at least consistent!) more testing

the 120-300mm has questions for me, but i think it is not so much back/forward but something with not being able to focus on the point i am trying for. be it lack of contrast, not fast enough, i dont know. To me this now seems as the camera not being fast enough +moving with the target compounded by my poor panning.

the 35mm is def not this, it is absolutely missing the focus point. but sometimes it produces pictures that completely miss. but this never happened in the tests. could it be that my focus point is on target but due to back focus its actually focusing on something 3 feet back?
Click to expand...

It shouldn't be able to focus on anything behind or in front if you're using the centre AF point only. Plenty of light and a good target with nice sharp contrast and there should be no reason to miss focus.

If focus is missed then you should see the area in focus either behind or in front of the target itself. If everything is blurry then the lens has issues, especially if its like that in liveview mode.
 
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