Keep in mind that it's not terribly uncommon for a certain lens/body combination to need a microfocus adjustment (that's why the option is included on newer cameras). I have a 70-200 f/2.8 L IS that requires a heavy MF adjustment on my 50D, yet no adjustment is required on my 7D.
When you set up a controlled test, make sure to do it at 100 ISO--you don't want noise (and itsautomatic removal) to skew your sharpness results.
Thanks for the tip, Sean. Is microfocusing adjustment particularly difficult/involved? Any way I could seriously screw up the lens? I have almost no familiarity with it beyond a vague understanding of what it is.
And thanks for all the suggestions. These forums have been invaluable for me the past year.
Originally Posted by gbc
I'm sure there are optimal ways to do a MF adjustment and not-so-optimal ways. If you do it incorrectly, as far as I know, there's no risk of doing any damage to your lens and every adjustment is reversible (there might be damage to your reputation if you miss focus on every shot of a photographic session, however).
To dial in the MF adjustment on my 70-200, I set my camera on a tripod on one end of the largest room in my house (including a few feet of a hallway). I focused on my camera bag logo at an average portrait focal length and distance, and dialed in the MF adjustment until it was sharpest. After that, my keeper rate for the lens improved significantly. I haven't accessed the MF adjustment since.
It's not particularly hard, it seems. Before I got my fancy LensAlign tool, I used a [url="http://www.focustestchart.com/focus12.pdf]cut-out paper chart[/url]. With my T1i body (which lacks the microadjustment feature) and that chart, it seemed myEF 100mm f/2.8<span style="color: red;"]LMacro IS USM was front-focusing a bit, while all my other lenses were ok. But, there was nothing I could do about that myself - lens and body would have had to go to Canon Service. Now, with my 7D andLensAlign Pro, I just tested my100mm f/2.8<span style="color: red;"]LMacro, and pretty close (though I may adjust it a bit). The only other lens I've tested so far - my EF 85mm f/1.8 USM - seems to be back-focusing a bit. These are only single test shots, as well. I really need to shoot 3-5 shots, obviously. I haven't done adjustments yet (having a 2 year-old daughter means not having long blocks of time!), but the procedure seems to be simple.
Thanks for the help, guys. I tried a little microadjusting, and I think it may have solved the problem. Didn't have a whole lot of time to set up proper lighting or anything, but just from a quick test, the problem was apparent.
This is the lens prior to adjusting, at 18mm, from about 8 feet away:
[img]/cfs-file.ashx/__key/CommunityServer.Components.UserFiles/00.00.00.30.41/zero.jpg[/img]
This is the adjustment at +10:
[img]/cfs-file.ashx/__key/CommunityServer.Components.UserFiles/00.00.00.30.41/plus10.jpg[/img]
(Glad I finally found a use for the bizarre, shiny string my girlfriend has lying around)
The problem is only apparent at wider focal lengths. Is that normal for this kind of problem? I've had this lens for a while, but most of my shots are around 40-55mm, so it took me a while to really notice the focusing problems. I also bought this lens refurbished. I figured that a refurbished lens would've been put through its paces, since it had to be repaired anyway, but I guess I should've checked it out better.
Anyway, thanks again everyone for the suggestions. I'll have to do more tweaking, but I think this is the right track. I can't thank you guys enough. I was really going crazy over this.
Check out that the long end is still sharp enough. If not, send the lens back I say.
Regarding the "+10", I believe it's normal. I gave a "-6" adjustment to my 17-85.
Looks better! I second Oren's recommendation - test again with the lens at a longer focal length. In a previous post on AF Microadjustment (AFMA), one person mentioned testing a 24-105mm f/4L and finding that it needed +5 at one end of the range, and -5 at the other end of the range - as a compromise, AFMA was left at 0. So, test at both ends of the range, and then find a compromise that works for you, probably weighted toward whichever part of the zoom range you tend to use more often.
So i've been struggling with this issue for a little while also... i havent tested this yet but i can already tell this is my problem with my 17-55... its just no longer sharp. I also use a 70-200 f/2.8 L thats sharp as a tack... thats how it was easy to tell my 17-55 between 17-25mm was having issues.
I have a 30D that apparently does not have AF MA... now what?
Your only real option is to send the lens into Canon. Be aware that they may need to calibrate the body along with the lens. Good luck!
Posting Permissions
Reply With Quote