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Help focusing issue !!! for sigma 35mm f1.4 Art lens


11 Sep 2014 12:41PM
Hello Everyone I'm a new guy here

I recently got Sigma 35mm F1.4 Art lens for my Canon Rebel T4i. Since the day one I have been facing bad focusing issues. I didn't notice that issue till I saw the pictures in the big screen. All of them were blurred out, total misfocus and front/back focussed Sad I thought giving it to the service would correct the issue, but even that didn't help as the service person even couldn't get it right with the Sigma dock and their optimization software.

I thought of buying the sigma dock for myself and calibrating the lens myself but Im little confused with the calibration values which would be suitable for my camera. Earlier I used the same 35mm lens of one of my friends and there wasn't any issue with that one.

I have also few questions regarding this, which would be very appreciated if anyone could help answering them to me.

1. is calibration required everytime with the change of camera ? if really so, then how come the lens i used earlier was totally perfect ?
2. is there any default calibration settings which would help to eliminate the issue irrespective of the camera ? if so then please provide the same

I was very much disappointed with the issue im facing with my copy and I wait for someone who can help me solve this issue

Thanks in advance !

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Chris_L 5 5.2k United Kingdom
11 Sep 2014 1:54PM
If it's out to the point where a service guy with Sigma software can't get it right it needs to be replaced under warranty.

This isn't a very common question in this forum, I suspect the reason for that is it's not an everyday issue - I've never had to worry about microfocus adjustments and fine calibration of my lenses; maybe I've just been very lucky or maybe quality control of body and lens has meant I haven't had to worry.
mikehit 10 8.0k 13 United Kingdom
11 Sep 2014 1:58PM
My questions would be what aperture are you using (DOF with 1.4mm can be horrendously thin and need really excellent focus) and what size are you looking at them on screen?
11 Sep 2014 2:02PM
@Chris_L

The service guy we had here in our place doesn't seem to be having much knowledge with the software stuff. And that too since the dock was released just this year, he was not well aware of operating it. It is under warranty as it is still 2 weeks old. I would like to take the chance of replacing as last remedy.

I still believe that with proper micro adjustment settings, the lens may function properly and I hope someone will help me regarding the MA calibration of lens suitable for my camera body.
11 Sep 2014 2:04PM
@mikehit

I used f1.4 for the pictures I shot. The closer ones which are about half a feet distance are sharp enough, but the ones which are more than 5 feet away seem to be out of focus and also sometimes largely backfocused. I saw the pictures in my imac's 21" screen.
Chris_L 5 5.2k United Kingdom
11 Sep 2014 2:05PM
Have you done any tests with rulers or graph paper etc to check focus point achieved versus actual focus point selected by the camera?
11 Sep 2014 2:13PM
Chris_L

yes, Chris. I did it and the focus was ok with closer distance as I mentioned and going farther is shifting in 2-3 increments. When I correct that and check again, the previous points which turned out to be in focus are out now. While in camera, it shows as perfectly focused and after seeing the shot, it's not.

Also the center point of the camera is focusing pretty well most of the times. But the other focus points like top/bottom, left/right corners are not properly working.
Chris_L 5 5.2k United Kingdom
11 Sep 2014 2:39PM
That's pretty counter-intuitive my experience has been the wider the aperture of the lens the more likely it is that other focus points work better.

I can't see how the fault can be rectified if adjusting one thing bang on puts out another thing then visa versa.

Looking at search results like these it's common for this type of lens - maybe there are some there that you've not encountered with possible fixes?
mikehit 10 8.0k 13 United Kingdom
11 Sep 2014 3:08PM

Quote:shifting in 2-3 increments.


When doing your focus tests, what is the focus distance and how far out of focus is it in millimitres/centimetres?
You say you are looking at the images on your 21" screen but are they 100% view? 50%? If you are viewing them at 100% and looking at them from 20" you are very close to what is in effect a 6-foot print.
11 Sep 2014 4:34PM
@Chris_L

Yeah I read others facing similar issues too but someone I could possibly find an answer to the issue anywhere except 'calibrating with the dock properly'
I wish if I had any possible calibration data of any others who have encountered the same issue
11 Sep 2014 4:37PM
@mikehit

I tried at in feets 0.99, 1, 1.5, 2, 3

Im directly seeing the preview of pictures in photo viewer without any zooming in and even then the pictures are blurred out or with some kind of distortion in them as if they were taken at a very low shutter speed
mikehit 10 8.0k 13 United Kingdom
11 Sep 2014 6:13PM
Thanks - how far out of focus are they (in centimetres/inches)?
Can you post any examples here?
11 Sep 2014 7:13PM
@mikehit

They were 1-5 increments +/- with the increase of the distance

I cannot post the pictures shot earlier as they were one of my business clients. I will post some pictures which I took around in my place
mikehit 10 8.0k 13 United Kingdom
11 Sep 2014 8:25PM

Quote:@mikehit

They were 1-5 increments +/- with the increase of the distance




Sorrybut that mean absolutely nothing to me. What are 'increments'?
When it back-focussed, how far behind the intended subject was the plane of focus (in inches or centimetres, not 'increments')
When it front-focussed, how far in front of the intended subject was the plane of focus (in inches or centimetres, not 'increments')

It would be good to see some images when you have time.
11 Sep 2014 8:28PM
@mikehit

I meant centimeters. Sorry for being not so specific


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