5D III AFMA for Zooms - Adjust Wide or Telephoto First?

[RC]

While AFMA my lens, it occurred to that I might be making matters worse based on how I was testing zooms.

Here is my scenario: I setup and test my 24-105 for the telephoto end first. I determine that +5 is my ideal focus position at 105mm. I set the value +5 in the camera. Now I setup my camera for testing at the wide end. Common sense tells me I should change the telephoto value back to 0 while I test for the wide end at 24mm. Then once I determine both values, I enter them in the camera.

So is it best to test one end while the opposite end is set to the new value or to zero? My guess is zero or maybe it doesn't even matter. The manual does not specify anything this specific so I though I'd bounce if off the CR community.

Thanks

Note: I doubt it matters but I am using the LensAlign Mk II tool, plan to switch to FoCal in the near future.

Edit: The 5D3 can store 2 AFMA values (wide and tele) for zoom lens.

 

[PackLight]

I usually test it at the setting I am using first. After all if your first test at 24 mm shows no adjustment necessary then no need to go farther. But I have used mine extensively and know exactly what to expect.

It really doesn't matter where you start it is where you end.

Personally I favor the long end of a telephoto for settings, why is because the wide end is more forgiving because of the wider DOF.

Edit: sorry I misunderstood, I guess the 5D III allows adjustments at both end? Still I wouldn't think it would matter since the camera allows separate adjustments.

 

[Mt Spokane Photography]

I'd start with both at zero, and change either one first.

 

[Loswr]

If you're all the way zoomed to the tele end, it doesn't matter how the W setting for AFMA is set, the camera uses only the T setting. Same when zoomed to the wide end, the T setting is ignored. So, if you're just testing at the ends, order doesn't matter. For any zoom setting that's not at the ends, the camera does a simple linear regression between the W and T values (even if one is set to zero). If you want to test an in-between focal length (on the 24-105, I test at 24, 50, 85, and 105mm, to get an idea of performance across the range, and I test each FL at 25x and 50x the FL from the target), you must set both W and T to the same AFMA value.

 

[rpt]

I'd start with both at zero, and change either one first.

Yes, agree. I use FoCal now and it starts with telephoto and an AFMA setting of 0. I would take three test shots first at 0. Then depending on where the focus appears, set MA to 5 or -5 if the shift is small. If it is large, I'd set it at a higher absolute number. Once you are in the general ballpark then you can fine tune it. Take 3 shots for each setting and compare all. That way if one screws up you still have 2 to base your judgement on.

 

[PackLight]

If you're all the way zoomed to the tele end, it doesn't matter how the W setting for AFMA is set, the camera uses only the T setting. Same when zoomed to the wide end, the T setting is ignored. So, if you're just testing at the ends, order doesn't matter. For any zoom setting that's not at the ends, the camera does a simple linear regression between the W and T values (even if one is set to zero). If you want to test an in-between focal length (on the 24-105, I test at 24, 50, 85, and 105mm, to get an idea of performance across the range, and I test each FL at 25x and 50x the FL from the target), you must set both W and T to the same AFMA value.

Are you sure it is linear and not based on any type of curve?

 

[Loswr]

Are you sure it is linear and not based on any type of curve?

Pretty sure. Especially since I tested it with 4 different lenses set to W = -10 and T = +10:

 

[PackLight]

Are you sure it is linear and not based on any type of curve?

Pretty sure. Especially since I tested it with 4 different lenses set to W = -10 and T = +10:

Did you find the lenses accurate in the mid ranges?

 

[Loswr]

For the most part, yes.