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03-30-2013, 12:06 PM   #1
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K5IIs and Sigma 30mm focus issues

Been using the Siggy for a week or so now and not really checked for any focus problems until today.

I took some shots using the far left and far right focus points. At f1.4 the camera confirmed focus but nothing was in focus at all. the whole pics came out as a blur. It got slightly better starting at f2.8, but not great.

Once you move in to the next left and right focus points in, the problem goes.

I tried out the 18-135 and this shows no such issues.

Is this common with primes or Sigma lenses?

Just a quick edit... if I use MF i can get what i want in focus on both the left and right focus points.

I tried fine tuning the AF to both -5 and -10 and +5 and +10 and it did not make a lot of difference if any.

Edit again... was using far left focus point and item in frame on front right was in focus! Think I have issues with this lens!!


Last edited by JayX2A; 03-30-2013 at 12:56 PM.
03-30-2013, 01:03 PM   #2
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with fast lenses the field of focus is often quite curved, so the focus across the frame wide open can be all over the place. also these lenses aren't very much corrected ate the edges so the focus can easily be fooled.

and also... the edge focus points aren't that accurate to begin with.
03-30-2013, 01:19 PM   #3
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Ahh thanks for the reply. I'm going to to a focus chart test just to check its not back/front focussing.
03-30-2013, 02:20 PM   #4
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fast lenses can be problematic though, good luck. I returned my first 30mm when I bought it. I could not get it to focus right. second one was almost perfect out of the box. you need to get a bit lucky.

03-30-2013, 02:25 PM   #5
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Seems to be focussing ok in most occassions bar the far left and right points. I'm not sure how often I would be using them with this lens anyway! Apart from that the IQ seems very good. Maybe its just as you mentioned, the curved view and the fact the sigma is meant to be quite soft at the edges.

Not sure whether to try another copy or not. It might just be how this lens behaves TBH, I doubt many people have tried the left and right focus points with it!
03-30-2013, 02:54 PM   #6
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Where did you buy it? Did you buy it at a good price? I'm still looking for this lens.
03-31-2013, 06:20 AM   #7
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All of these fast lenses have soft corners and a curved field,it's the nature of the beast.

If you can get the center focus to shift infront and back the subject with -10 and +10 focus adjustment it mens you can adjust the lens.
My first sigma needed over -10 so i could not get it right on my camera.

Both the lens and camera have a small error so if my camera has -5 error and the sigma lens -7 the effect would result in -12 so out of the range of adjustment.
Someone else with +7 camera would be very happy with that lens.

These numbers are actually measurements of 10 μm (0.000001 of a meter) just to show how small these errors actually are.
04-02-2013, 01:38 AM   #8
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Camera is not back or front focussing in the centre from what I can see. I'm thinking it may be the nature of the lens as mentioned that the far left and right focus points send it in to meltdown!

Can anyone test theirs to see if it does the same?

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