Another focus problem. Camera or the lens? Sigma 70-200EX

[Chris1le]

After reading the latest couple of focus questions I decided to check out my Sigma 70-200EX. Sometimes the shots seemed sharp while other times they do not. It seems to be front focusing. I have two Canon lenses 28-135IS and 50mmf/1.8. They seem to be close to dead on.

Should I send the lens back to Sigma? Is there an adjustment that they can make?

Here are the TEST IMAGES (http://www.pbase.com/chris1le/focus)

[scottbergerphoto]

Your right. The lens seems to be front focusing. This is most noticeable at wider apertures as expected. Lenses can be calibrated. I would send it in for warranty repair.
Scott

[vvizard]

I suspected the same thing on mine, and "verified" it with testing. Although, I used a polarizer and it was shot in dim lightning, so I was told on the forum the test was not any good. The next day I went out to shoot an outdoor event. Oh my God this lens delivers =D So I thought that the "price" I have to pay for beeing without this lens for some weeks is higher than the "price" of maybe not beeing spot on shooting rulers. I know that if the lens have a fault, it's real nice of me not claiming a return, but then again, I don't do macro-like work with it, and that's the only place where I've had troubles with focusing. It doesn't see much use through winters though, so I might send it in for repair next winter if I feel like shooting more rulers, and find out. But in everyday shooting, this lens is stunning in my case :)

[Chris1le]

Well, I usually do NOT shoot rulers. This was my first "ruler" shoot. :D I just did this test after reading some of the other focusing posts. The thing is, I've been noticing that when I focus on say a squirrels eye his nose would come out sharp as a tack while the eye would be soft. I agree though being without the lens will suck. Maybe I'll just shoot at 5.6 or above until the winter. Kind of defeats the purpose of the lens though. :cry:

[robertwgross]

If you had a Canon body and a Canon lens, then you could ship the combination to Canon and let them check the body, the lens, and then the combination.

Since you have a Canon body and a Sigma lens, you won't find anybody who will work on the combination. Canon won't, and Sigma won't.

Theoretically, if the body is calibrated properly, and if the lens is calibrated properly, then they will work together fine.

---Bob Gross---

[Tom W]

It would be nice if they'd just put an adjustment screw on the side of the lens, under a little rubber cover. Then we could tweak our lenses and maybe even have contests. ;)

[CyberDyneSystems]

Chris.. did you have any filters mounted for te focus test?

I suddenlydeveloped "focus issues" with this Sigma after enjoying it for a while with no problems.. after shooting rulers and CDs for a while.. I fianlly realize I had recently installed a "better" UV filter tha the one I had purchased as a quicky originally...

Yep.. by removing the quality Hoya uv Filter.. all focus problems disappeared.

It had no problems with some other UVs I tested..

Give it a try.

[Chris1le]

Yes Cyber, I seem to remember you saying something about filters. I have been using a Canon UV filter. I tried it with and without the filter with the same results.

The body seems to be focusing properly with the Canon lenses. I guess I'll just send it back to Sigma with a couple of the pictures. Hopefully it will come back focusing properly. Other than this problem I like the lens. I do think I'll have to think twice about buying Sigma again though. :(

Yes Tom, that would be nice. I double checked but could not find an adjustment screw though. :lol: :cry:

[msvadi]

Just a thought:
what focal length did you use with the sigma lens? The target may be too small for long telephoto. Try to make a larger target and make the center focus line more contrasty (red, for example). See what happens.

Anyway, don't worry about the tests if you happy with the lens performance in usual conditions. Shooting target charts is not its main purpose. ;)

I know it's not easy. I could not get perfect test results with my 135mm 2.8 lens. But some test shots were quite good with 50mm (and some not good at all). So, I decided that the camera AF is okay. Next, I went back to the portrait shots I took with 135. Some were absolutely sharp (and some not, but it could be me and not the lens), so I decided not to do anything at this point. I may test the lens again with a larger target and better light conditions.

[vvizard]

In the computing industry, it's no secret vendors of graphic-cards optimize the cards specifically for the popular games used for benchmarking, or the popular dedicated benchmarking programs like 3Dmark. Maybe the next big hit now, is for Canon/Sigma/Tamron to optimize their lenses for rulers and ducks? At least, the first guy getting a new lens will probably find justaduck to photograph, and share it with his friends on a forum like this.. Then people will ask.. *hmmm* is that a slight focus-problem I can spot there, after I printed your image to A3, and went over it with a magnifying glass?, I would've checked it out.. So, out with the rulers and shots spot on. Back to forum and brag, and everyone agree, the lens is near to perfect... At least until you start using it for real things =P

I'm wondering when the first 100mm USM RULER! Will replace the 100mm USM MACRO =D