Micro-Adjust Question

[HaveVoid]

Hello All,

I recently had my 100-400 serviced for a very noticeable softness towards one side of the frame (variable either left or right with no pattern) and general focus issues. It was returned to me with the explanation that an element had come out of alignment and was "loose" causing rear focus to occur. Canon stated that "electrical adjustments were performed". Upon receipt of the lens, the Back focusing issue was still ever present, so I decided to adjust using MFA. I did this at 400mm using the generally accepted practices.

Yesterday was my first full day in the field post this adjustment, and I made several observations. The lens is fairly sharp at 400mm now( nowhere near where it was before the element came out of place, but alas...) but the rear focus gets really really bad the farther away you get from 400MM. 100MM is now practically useless. As the softness seems to be directly proportional to the distance from 400MM, would performing MFA at 200mm, make the overall range sharper?

Is there some sort of trick to MFA for zoom lenses?


HV

 

[bkorcel]

Generally what we've seen is that Canon manufactures lenses to focus sharply at maximum focal length (more or less depending on the camera model). The idea is that at wide angle your DOF is wide enough to absorb most of the error.

So the question is, where do you use the lens the most? 100 200 or 400mm? If you stop the lens down to F8 does it sharpen up at 100?

I owned the 100-400 for about a week before I returned it and it was always slightly soft wide open. It really needs to come down to F7 or F8 to sharpen it up. I returned it for other reasons...mainly the AF system was slow. I chose the 70-200 IS II with extenders.

Which camera do you have? Many of the newer cameras have MFA for both ends of the zoom range now.

 

[HaveVoid]

Thanks for the quick reply! I tend to use it across the gamut of focal lengths from 100-400 as I shoot primarily aviation, and encounter things from fighter to widebody airliner sizes in a given outing. I am shooting with a 7D primarily, with a 50D for backup.

 

[bkorcel]

Thanks for the quick reply! I tend to use it across the gamut of focal lengths from 100-400 as I shoot primarily aviation, and encounter things from fighter to widebody airliner sizes in a given outing. I am shooting with a 7D primarily, with a 50D for backup.

Well a "poor" way to do it is to figure out the MFA value for each end and set it before a shoot but if your aircraft are in flight it's not easy to do that. I think you will just need to use a high F/stop to compensate for the issue. If you try to meet it in the middle, your 400mm end will get pretty soft and thats where you need the accurate focus the most.

I've read posts here where people have performed MFA adjustment tests of their zooms and they are all over the place through the zoom range....and these are with "L" series lenses. You could also bug Canon about adding the ability to MFA at wide and tele for zoom lenses to the 7D firmware.

Maybe someone here can comment on their MFA test results with a 100-400 L lens.

 

[vbi]

I think your only option is to return it to Canon as there is no way MFA can accommodate such variances.

 

[AmbientLight]

What I would do in such a situation is to send the lens back in for correction. From what you have described it appears that the service has not been effective in restoring your lens to what it could do before, since microadjustment alone coudn't fix the autofocus issues.

The only alternative to this would be to sell the lens to some innocent, unsuspecting victim, err buyer and to buy a new 100-400. :-X

 

[RC]

I would love if Canon would offer (and sell) a firmware update to store multiple AFMA value for bodies that don't support that. I know, not gonna happen since it might cut into sales of new bodies.

Anyway, I'm anxious to see what the big guns have to say about this as well since I have the same question. I just got done adjusting for my 24-105. Using Neuro's procedure and the LensAlign MkII, I got -2 at 24mm and +3 at 105mm. I set my camera at +1 because I expect to shoot more longer distances and focal lengths.

BTW, just got this lens back from Canon Service (Irvine, CA facility). I sent it in because it had a 10 point swing in AFMA values from 24-105mm. They reported:

"...adjustment of the mechanical chassis was incorrect causing inaccurate auto focus. The mechanical chassis was replaced...."

 

[Mt Spokane Photography]

It is common to have the focus accuracy vary somewhat over the zoom range, but it should not be extreme. I mostly use my 100-400 at 400mm, and its very sharp wide open. I'd send it back to the repair service describing the issue, there seems to be something wrong.

 

[HaveVoid]

Thank you all for your input. I think I will end up sending it back in, as the repair is still warranted. I had hoped that becoming a CPS member would have addressed the history of improper repair completions that I have with Canon, but perhaps they need two cracks at it. It took them three shutter replacements and two electrical adjustments to solve the issues with my 50D (don't ask me how they mis-wired the electricals twice).

HV