Canon 17-55 IS : micro adjustment on 7D ?

[lapino]

I never used this feature, but lately noticed some of my shots being (unexplainably) oof. So I started messing with the micro adjustment for AF and it seems my 17-55 needs about +15. It's sharp then when taking pics pretty upclose, but when I take pictures from a distance the image doesn't seem as sharp.

So, what AF adjustments do your 17-55's need on a 7D?

[Rocky Rhode]

MFA was intended to be used for Prime lenses; you can MFA a zoom but you will only have that one focal length adjusted. Since the 17-55 is not parfocal, you need to MFA both at 17 & at 55; a feature that I don't believe that 7D has.

[2n10]

I haven't done it on mine. From my understanding on zoom lenses if you AMFA on the 7D for one end then the other end may suffer for it. Suggestions seem to be if you use the full range average the adjustment from both ends. If you use mostly at one end then AFMA at that end.

[lapino]

Ok that explains a lot. Think I'll leave it at 0 then. Was not aware that MFA was specifically intended for prime lenses.

[Invertalon]

I used to bias zoom lenses with the 7D and 5D2 closer to the tele end since depth of field is more shallow. For example, if it needed -2 at 17mm and +4 at the 55mm focal length, I would probably set it at +2.

[cthetoy]

I microadjust my zoom lens. i microadjust the wide angle first and then the zoom end. Wide is +3 and Zoom is +6 so I leave it a +4. A lot better than leaving it at zero.

If there is a wide discrepancy between the wide and zoom then I would send it to Canon to recalibrate your lens.

The 5d3 cameras allows you two enter two MA settings: One setting on the wide end and one settings on the zoom end

[TeamSpeed]

Originally Posted by lapino

Ok that explains a lot. Think I'll leave it at 0 then. Was not aware that MFA was specifically intended for prime lenses.

It is not intended for prime lenses, it is designed for any lens. You just either set the MFA value to whatever is needed at the focal length you shoot at most, or just average the value needed. Steve has a good reason for what he MFAs at as well, I would refer to that earlier reply as another possibility.

Canon has since introduced new MFA on the 1DX to allow MFA at the wide end and at the telephoto end of a zoom lens, further enhancing the MFA functionality.

[hollis_f]

Originally Posted by cthetoy

I microadjust my zoom lens. i microadjust the wide angle first and then the zoom end. Wide is +3 and Zoom is +6 so I leave it a +4. A lot better than leaving it at zero.

Yup, good decision.

People seem to forget that it's a MICROadjustment. It makes very small changes. For most lenses the difference between +3, +4 and +6 would be hardly noticeable, and almost certainly close to the natural shot-to-shot variation.

[TeamSpeed]

Once you hit +/-7 or so, I think you would notice it, because at this point, you have shifted your DOF about one entire "dof-wide" amount. I forget the exact amount that Canon documents, but I think 1 value equates to 1/8 the DOF maybe?