AF micro adjust for a 70-200

EspressoJunkie

EspressoJunkie

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Greg
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I've noticed that my Tamron 70-200 is front focussing somewhat.

I've gotten it set to +12, which definitely improves things, just with some rough testing but im going to do it properly over the weekend.

I know how to do the whole procedure but am I right in thinking for a zoom in best doing it for the far end (ie at 200m)? I noticed the front focussing when shooting something far away (is infinity the correct term?) so I assume it is.

I know Canon have an option for adjusting either end but on Nikon its just the one.

Any advice?
 
Id adjust for the focal length and subject distance that you use most. Which I would imagine for most people would be the long end, and fairly close, which would also where the front focus would be most noticeable.
 
The problem with micro adjusting a zoom is that it may require different levels of adjustment depending on the focal length. On my old 5D mk3 I had it adjusted differently for 70 and 200.

Prime lenses are easier to adjust for this reason

I upgraded my Tamron 70-200 to a Nikon VR2 as I've had constant issues with focus etc with that lens. 5 out of 6 copies problematic. No good having great optics and crap AF that varies from body to body!!
 
F/1.4 said:
The problem with micro adjusting a zoom is that it may require different levels of adjustment depending on the focal length. On my old 5D mk3 I had it adjusted differently for 70 and 200.

Prime lenses are easier to adjust for this reason

I upgraded my Tamron 70-200 to a Nikon VR2 as I've had constant issues with focus etc with that lens. 5 out of 6 copies problematic. No good having great optics and crap AF that varies from body to body!!
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See its not that it's bad per se, you would barely notice it at close distances and its really only at 2.8 but it is there so I want to get it sorted. Luckily though it does seem to be within the level that it will be able to be corrected in camera.
 
EspressoJunkie said:
Thanks for the replies. Does anyone have any favourite method of testing?

At present i just use a test chart on the floor with the camera on a tripod at 45°
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Target must be flat, and square to the camera, on a tripod. Use centre-point AF, on the face of the box in an area with some graphic elements for the camera to lock on to easily, to the side closest the ruler. Keep the distance realistic, and not too close - something like you'd shoot a portrait with a lens like that. Focus, then enlarge on the LCD to see where the sharpest point actually is on the ruler. Adjust, defocus lens, repeat until it's right.

Test at short, middle and long focal lengths to get an idea of any variance (prolly won't be much) and try for a decent compromise. Maybe bias towards the longer end as that's most likely where you'll be using lower f/numbers with shallower DoF.

 
The longest I've done is 100mm.

Out of interest, why is it more difficult than other methods, and what method do you use for the longer lengths?
 
EspressoJunkie said:
I've noticed that my Tamron 70-200 is front focussing somewhat.

I've gotten it set to +12, which definitely improves things, just with some rough testing but im going to do it properly over the weekend.

I know how to do the whole procedure but am I right in thinking for a zoom in best doing it for the far end (ie at 200m)? I noticed the front focussing when shooting something far away (is infinity the correct term?) so I assume it is.

I know Canon have an option for adjusting either end but on Nikon its just the one.

Any advice?
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That's a bummer Greg zooms can be a pain to fix, hope you get it sorted I remember posting in your thread when you where considering changing your 85 for the zoom. Is there no way you can return the lens?
 
f/2.8 said:
That's a bummer Greg zooms can be a pain to fix, hope you get it sorted I remember posting in your thread when you where considering changing your 85 for the zoom. Is there no way you can return the lens?
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I've contacted the fella yeah but its a private sale so I'm at his mercy! He seemed like a decent sort through so hopefully we can sort something out.
 
HoppyUK said:
Target must be flat, and square to the camera, on a tripod. Use centre-point AF, on the face of the box in an area with some graphic elements for the camera to lock on to easily, to the side closest the ruler. Keep the distance realistic, and not too close - something like you'd shoot a portrait with a lens like that. Focus, then enlarge on the LCD to see where the sharpest point actually is on the ruler. Adjust, defocus lens, repeat until it's right.

Test at short, middle and long focal lengths to get an idea of any variance (prolly won't be much) and try for a decent compromise. Maybe bias towards the longer end as that's most likely where you'll be using lower f/numbers with shallower DoF.

Click to expand...

Just another note on this method, it's easy to scale it up and use for longer lenses at much greater distances. I've done it using the end of a wall as a target, with a plank of wood to the side in place of the ruler. Realistic testing distances are very important for all lens types but there are no 'rules' - the 50x focal length or 25x focal length suggestions are not always appropriate. The temptation is to go too close, so you can see any focus errors more easily, but this is quite likely to put the lens out at longer, more normal shooting distances.

The moire/monitor method is also good, and there's no reason why you couldn't put a ruler up the side of the monitor to check exactly where the sharpest point is. Without that, I find it quite tricky to decide exactly where the sharpest point is from looking at the patterns.

There is a problem with some other kinds of target, at least in theory. If the target itself is angled, you can't be certain of exactly where the AF system is trying to focus, and even using just the centre AF point, that can be sensitive to an area quite a bit bigger than shown in the viewfinder. Also in theory, the AF system works best on random shapes with good contrast, rather than straight lines that can clash with the alignment of the AF sensors. That's more likely to affect older cameras though, that don't have AF micro-adjustment anyway LOL
 
Well after more testing I think I've got it down. The front focus was really only affecting subjects further away and I'm happy enough that the AF adjustment has sorted it. I know its maybe not ideal for a zoom but this one is too sharp to let go.
 
simon ess said:
The longest I've done is 100mm.

Out of interest, why is it more difficult than other methods, and what method do you use for the longer lengths?
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The screen is to small to be able to see if you are in focus properly. :(
My wife wasn't pleased when I suggested taking the 55" Telly outside to calibrate my lens. :)
 
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