Backfocus...

Cameron

I've been having a great time with my new 30D but recently have seen a trend of backfocusing with my 70-200 f/4 L lens. I tried shooting some test shots over the weekend by placing several objects in the viewfinder, each an inch or so further back from the one next to it. It is noticable at f/4 - the point of sharpest focus seems to be ~ 1-2 inches behind the area where I focused. I've confirmed focus points in Zoombrowser.
Because it's not THAT far off, it has only been a problem at below f/5.6 or so. From reading on other boards, it seems this lens has a history of backfocus problems and I'm thinking about sending it in for calibration.
I'm at work right now and won't be home until morning - I can post some samples then. Note, I do not experience any problems with my 50mm f/1.8, my 100mm EF macro, or my (borrowed) 17-85 EF-S IS lens.
My questions are:
1) Does what I'm describing warrant calibration or is it within acceptable limits?
2) Regarding calibration, I've heard conflicting advice regarding whether or not the camera should also be sent in for calibration as well (I recognize that lenses and camras are calibrated independently to standards and not to each other).
3) Assuming I send it in, does it matter if I send it to Jamesburg, NJ or Irvine, CA? Is turnaround faster at one? I live in Kansas City so both are just over 1,000 miles from me..
4) Any idea what typical turnaround time is?

I just want my most expensive lens to focus as accurately as my $80 50mm... :dunno

Cameron

Bob Bell

CSwinton wrote:

I've been having a great time with my new 30D but recently have seen a trend of backfocusing with my 70-200 f/4 L lens. I tried shooting some test shots over the weekend by placing several objects in the viewfinder, each an inch or so further back from the one next to it. It is noticable at f/4 - the point of sharpest focus seems to be ~ 1-2 inches behind the area where I focused. I've confirmed focus points in Zoombrowser.
Because it's not THAT far off, it has only been a problem at below f/5.6 or so. From reading on other boards, it seems this lens has a history of backfocus problems and I'm thinking about sending it in for calibration.
I'm at work right now and won't be home until morning - I can post some samples then. Note, I do not experience any problems with my 50mm f/1.8, my 100mm EF macro, or my (borrowed) 17-85 EF-S IS lens.
My questions are:
1) Does what I'm describing warrant calibration or is it within acceptable limits?
2) Regarding calibration, I've heard conflicting advice regarding whether or not the camera should also be sent in for calibration as well (I recognize that lenses and camras are calibrated independently to standards and not to each other).
3) Assuming I send it in, does it matter if I send it to Jamesburg, NJ or Irvine, CA? Is turnaround faster at one? I live in Kansas City so both are just over 1,000 miles from me..
4) Any idea what typical turnaround time is?

I just want my most expensive lens to focus as accurately as my $80 50mm...

Cameron

That doesnt sound like a back focusing problem. If it was that issue, it should do the same thing at all focal lengths. 1-2 inches is so significant that it should be out at all FL's. I guess your DoF could be masking it at longer focal lengths.

Don't use the 45 degree test they can be way off on a good lens. Use a stuffed animal for the test. Make sure you are using a tripod and not moving things around or changing light conditions.

They bench test your lens. Some people calibrate lens to body but I have 8-9 lenses and I wouldnt send them all in.

I have heard good and bad from both sites.

I think non CPS turn around is around 2 weeks in the US and 3 weeks in Canada.

Cameron

Bob - It does it at 70mm and 200mm when the aperture is, say f/11 the DOF is large and you don't notice it.

I didn't use the 45 degree test.. the stuffed animal sounds like a good idea. I'll try to post samples in the morning when I get home. Thanks for the reply

Red Bull

If it continues to back focus I would send it in, even if it is a little bit. You paid good money for that lens, you deserve to have a good lens without focusing problems. I have the same lens and I do not have any focusing problems (that I have seen so far.)