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PostPosted: Mon Aug 04, 2008 12:37 pm 
Hi,
Does anyone know of any focusing problems with this lens? I had a fair few photos that looked out of focus, so I did a test with my Canon lens, and the Sigma does look to be mis-focusing. I made sure the exposure settings etc were identical.

Thanks

Shirley


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PostPosted: Mon Aug 04, 2008 12:54 pm 
Is it focusing behind or in front of your selected area? If so, send it back to Sigma for re-calibration.


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 Post subject:
PostPosted: Mon Aug 04, 2008 1:04 pm 
Hi Graham

it is inconsistent, sometimes in front, other times behind. I have just done another test, and it seemed fine. I have spoken to the shop, and will take it back when they have another lens in to replace it with. In the interim, I will do some more tests. I am fairly sure it isn't my 40D as I have had it since christmas and not had any focussing problems.

Thanks

Shirley


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PostPosted: Mon Aug 04, 2008 2:40 pm 
I think a wrongly calibrated lens does one or the either. It's probably a different issue then but the shop is taking it back so that's okay I guess!


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 Post subject: Same problem here..
PostPosted: Fri Aug 15, 2008 5:28 am 
Shirley:

I use this lens a lot shooting weddings - mostly on the beach. I also am using it on the 40D. Prior to that, I was using on the 20D.

I have noticed inconsistencies in focus accuracy, and have wondered whether the Sigma is the problem or not. I always use the center focus point on the 40D & know its tendency to lock on an area of high contrast - usually behind the subject. I always aim the center focus point at the middle of the subjects body to avoid locking on something just over their shoulder. -Yet I still will get some inconsistent results - some are tack sharp & a few will be slightly out of focus.

Recently, I began reviewing the EXIF data & noticed that there are variations in the distance-to-subject data from sets of shots taken within seconds of each other. These are shots taken with no variation in the focal length & no changes in actual distance-to-subject, yet the data varies by 1 to 2 meters! I am assuming that the lens is responsible for providing this data. Someone please confirm or deny this.

I'm anxious to read the follow up on your findings. Please post a follow up! So many people forget to post a detailed account once they have found a solution.

I love the range of this lens, but may have to replace it with some L-glass soon!


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 Post subject:
PostPosted: Fri Aug 15, 2008 6:05 pm 
Hi

the shop replaced the lens for me. I took in some photos that clearly showed the problem.
The new lens is much better, although I think there may still be an issue with mis-focus from time to time. I haven't yet had a chance to try it out properly. I am going to Wales for a week soon, so will give it a really good test then.
Could you explain what you mean by EXIF data?
Many thanks

Shirley


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 Post subject:
PostPosted: Fri Aug 15, 2008 6:44 pm 
shirley wrote:
Hi

the shop replaced the lens for me. I took in some photos that clearly showed the problem.
The new lens is much better, although I think there may still be an issue with mis-focus from time to time. I haven't yet had a chance to try it out properly. I am going to Wales for a week soon, so will give it a really good test then.
Could you explain what you mean by EXIF data?
Many thanks

Shirley


Hi Shirley

I always shoot in RAW mode. The EXIF data is retained with each image file & contains data such as aperture, shutter speed, time, date, subject distance, lens used & focal length at time of shot, plus much more info. I believe this info is also included when shooting in JPG output mode.

Most image editing/conversion programs have the option of viewing or extracting the EXIF data.

I hope this answers your question.


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