Help with eBay/back focus situation plz!

[iris chrome]

Ok, so a friend of mine recently asked me to sell her Sigma 120-400mm lens on eBay. Which has already sold but the buyer just sent me an email saying that the lens has back focus issues at 400mm. Before I auctioned the lens, I did some tests of my own to make sure that it works properly and I also took my friend's word that the lens works in perfect order. Right now, I'm not sure if this is a case of nitpicking, buyer's remorse or maybe the buyer is just not used to working with 400mm on a DX (50D). Another thing that's worth noting is according to the UPS records he got the lens, tested it and emailed me all within 45 minutes. I'm sure that there are photographers out there than can test a lens completely in that short amount of time but I'm not sure this guy is one of them.

I've asked him to email me a picture at 400mm and I'm also getting in touch with my friend (the former owner of the lens) to see if she has any pictures taken at 400mm. My question is now that I don't have the lens anymore, how can I test the picture for back focus? Also if there is a back focus problem, wouldn't it be across the whole range of the lens and not just at 400mm? Can anybody tell me if 50D has a focus fine tuning and what menu do I get it from?

 

[Gothmoth]

well you can´t say for sure as long as you don´t know how he has tested for front/backfocus.

some make fokus tests with a 400mm at 5-6m distance in the livingroom. :
and maybe they notice a focus problem... then they shot at "normal" distances (i mean i seldom shot objects that are only 5m away with a 400mm lens) and it´s working perfect.

Also if there is a back focus problem, wouldn't it be across the whole range of the lens and not just at 400mm?

no.

Can anybody tell me if 50D has a focus fine tuning and what menu do I get it from?

microadjustment is not for zooms. it´s for prime lenses.
that is part of the question above. the focus problem can happen at some focal lenght.
if you adjust for this one focal length then other focal length will have a back/front focus problem.

but when 400mm is the important point for him he can try to adjust it.
the 50D has microadjustment.

http://www.northlight-images.co.uk/article_pages/cameras/1ds3_af_micoadjustment.html

Canon's suggested Micro Focus Adjustment

This is Canon's suggested technique - I cover much more about using similar techniques in my review of the SpyderLensCal device.

■Mount the camera on a good tripod.
■Set up a target for the camera to focus on. The reference target should have sufficient contrast for the AF system to detect. It should be flat and parallel to the camera's focal plane, and centred.
■Lighting should be bright / even.
■Camera-to-subject distance should be no less than 50 times the focal length of the lens. For a 50mm lens, that would be at least 2.5 meters.
■Set the lens for AF and the camera for One-Shot AF, and manually select the centre focusing point.
■Shoot at the maximum aperture of the lens via manual mode or aperture-priority. Adjust exposure level to get an accurate exposure. Use low ISO setting.
■If the lens has an image stabilizer, turn it off.
■Use a remote switch or the camera's self-timer to fire the shutter. Use mirror lock up as well.
■Take three sets of images at microadjustment settings of -5, 0 and +5, i.e, three consecutive images at -5, three consecutive images at 0, and three consecutive images at +5.
■Look at the images on your screen at 100% magnification.
■Take additional sets of test images at different microadjustment settings if necessary until the sharpest image is achieved.
■Register the corresponding microadjustment settings in the camera.


AF Adjustment notes from Canon
For best results, manually set the focus on the lens to infinity for every exposure before allowing the camera to autofocus the reference target.

Expect some minor variations in focusing accuracy within each set of three test images, even though they were all taken at the same microadjustment setting. This is completely normal, and is due to the tolerances of the camera's AF system.

Expect smaller microadjustment settings to have a greater effect with telephoto lenses, and vice versa for wide-angle lenses.

If you are attempting to set microadjustments for a zoom lens, it is important to realize that the camera's setting may only be accurate for the focal length setting you test. The instruction book suggests testing at the longest focal length of the lens, but you may find it more efficient to choose the focal length you use most often.

anyway.. if the buyer does not like the lens you have two choices.
take the lens back.... or get a negativ feedback.

 

[fred_jb]

I have used the same lens on both 50D and 5D Mk II cameras and needed different amounts of MFA with both, which despite it being a zoom, seemed to work quite well.

I suggest you point out that it is the lens/camera combination that dictates focus accuracy and ask if he has any other long telephoto lenses which focus accurately on the same camera. The implication is that it is just as likely to be his camera which is out as your lens.

You could also ask if he has much experience with long lenses - soft pictures could be due to low shutter speeds - you could ask if he has tested on a tripod with IS turned off to eliminate this.

This should at least give him somehing to think about. You could follow that up by suggesting that he tries using the MFA on his 50D and let you know how much correction he needs at 400mm.

If after this you are convinced that he has a genuine problem, then you could offer to pay all or a proportion of the cost of sending it in to Sigma for calibration, making clear that this would be in full and final settlement of the problem, with any remaining issues being down to his camera. I did this recently with a Sigma 100-300mm I sold - the calibration wasn't expensive (in the UK) and ended up with both parties happy and giving positive feedback.

Fred

 

[DynaMike]

Tell him to use the MA and stop complaining. There's no way a seller can guarantee a used lens will perform perfectly aligned focus on another camera because of the manufacturer tolerances. Buying used gear you have to assume that you'll need to put out more cash to get a CLA done on it and calibrate it to your body if you don't have MA. Plus how are you suppose to know that they set up an accurate test.

 

[jfretless]

I have been buying and selling Camera equipment on eBay since the last century...

I'm afraid when push comes to shove, the buyer will submit a case with eBay and almost always side with the buyer and have the seller refund the money.

After 11 plus years of perfect and loyal service to eBay as a buyer and seller, I had my first dispute. It was regarding baseball glove I sold, but none the less... It was marketed as a 12" glove, I clearly stated it as so, the buyer claimed it was smaller that 12". We went through the dispute process, supplied eBay with all the info, thought I had a bulletproof case and eBay quickly sided with the buyer. I was furious.

The buyer eventually close the case because he was too lazy to send it back. ...but eBay lost my trust at that moment.

I said no returns in the auction. Didn't matter.
I included six images on the item. Didn't matter.
My perfect reputation built over 11 years. Didn't matter.

When I sell a lens... I clearly state that a lot of the photography community is obsessed with focusing issues and that the lens I am selling has worked flawlessly on no less than # of cameras owned. ...and that due to manufacturing tolerances, I can not guarantee that the lens will focus flawlessly with your setup. If you do not agree, please do not bid.

Short of putting that in your listing, you'll have refund the buyer's money.

oh yeah... NEVER sell anything for anyone. Friends, family... Not worth your time, headache, and reputation.

Good luck.

 

[iris chrome]

So the buyer emailed me back with the picture. Now I am a photographer myself although I wouldn't call myself an expert by a long shot and I certainly lack in the area of back focus issues since I've never encountered that problem before, at least I think, but I always thought that back focus meant that the area in focus is behind what you're trying to focus on. The picture he sent me though, was just blurry all over which confirms what I suspected from the beginning and what some of the folks here are saying. So next I asked him about his setup and he said he used it handheld and 400mm x 1.6 crop factor so effectively 640mm! I mean that's crazy. That lens is not light and I don't care how good an IS or OS it has, his chances of getting a sharp photo at that focal length are slim. I've attached the photo he sent me.

I want to try to avoid escalating this issue as eBay is not so friendly to sellers when it comes to things like this. I will see if I can somehow reason with him and get him to do a test using a tripod. I think (hope) that he's probably just new to photography and misinformed about what it means for a lens to have a back focus problem.

Thanks to everyone for their input. Everybody here was very helpful. Oh and btw, jfretless, I got a cut out of the sale 8)

 

[DynaMike]

yeah.. if there is no distinct focal point in the entire photo that means there is camera shake (or the AF completely missed). Not a backfocus issue. I doubt he would be able to hand hold the lens at that length and get a sharp shot. Is the exposure data attached to the pic he sent you also? That could be another point for you if he says he can hand hold it and get a sharp shot, but the info shows a low shutter speed for that length. You'll know for sure that he's not experienced with shooting a long lens.

 

[Mt Spokane Photography]

If the buyer is not happy, have him send the lens back. Its that simple. Then refund his money less shipping. Test the lens, and if its good, list it again.

There is really no other choice.

 

[awinphoto]

Up until about 2005 I always sold gear on ebay... ever since I've used craigslist... that way they can test it and if they buy it, it's their problem. Ebay I've had one person on on lens complain that there was a minor scuff on the barrel when the lens was extended, yada yada yada... It wasn't there when I shipped it... Some people forget about the 1/focal length rule and even gets more critical on higher MP lenses. MA is there for a reason. Also canonrumors also posted an article a while about about testing lenses and manufacturers specs and allowances so even if one camera shows great, it the other camera has a different tolerance in spec, the lens could be soft. Tell him to give you shots taken on a tripod with no camera shake and a fixed item such as a pole or person or whatever... That way he can tell what's going on... Long lenses also work better with monopods... try that...

PS MA works for zooms AND primes... use the prime on the most extreme (wide open zoomed to the highest focal length).. If you MA on that, everything else, while they may change, will fall into place nicely.

 

[Gothmoth]

PS MA works for zooms AND primes... use the prime on the most extreme (wide open zoomed to the highest focal length).. If you MA on that, everything else, while they may change, will fall into place nicely.

so you zoom a prime lens.. well.. that IS impressive!!

what works is written by canon and was quoted by me .. no need to talk about that:

If you are attempting to set microadjustments for a zoom lens, it is important to realize that the camera's setting may only be accurate for the focal length setting you test. The instruction book suggests testing at the longest focal length of the lens, but you may find it more efficient to choose the focal length you use most often

on most back/front focus issues with zooms you make one focal range working fine using MA and other working worse. but in some situations you can average out the problem. you change one very bad focus issue to a acceptable focus issue.... while you make good focus shift to slightly worse.

i have sold and tested a zillion lenses .. and while MA can work with zooms to say "all will fall into place nicely" is wrong.

 

[awinphoto]

From my experience, If there is going to be any slight change in front/back focus, it will be on the long end, that is what is the most critical... Understanding how the 1/3 front, 2/3 back focus works, if you can nail focus on the long extreme, when you zoom out to the wide end, the image usually will be in focus... There of course may be extremes such as if you have max MA on the long end, when moved to the wide end, it COULD be enough to change the relation of focus within your frame, but if indeed that is enough screw it up, it's worth sending the lens into the manufacturer to fix.

ps regarding zooming primes, you know where i'm getting at.