sigma 24- 70 2.8

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hotchef23

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just a quick question, just bought a new sigma as above.

there appears to be a slight softness miss focus when it is at 70 mm, with flash. i have been trying out lens close up on a persons eye, when i have taken picture and then magnify to fullest extent on camera the eye appears out of focus on one and then next is sharp(at fullest magnification)
if i take shot at say 68 mm then it tends to be sharp each time.

ranging in appeture as well from 2.8 to 5.0 so as to try and give a better test range, again varing results.

have tried it at various iso settings to increase speed so the time is bigger than the lens so 70 mm 1/80.

has any one else had similar problems or is this the same with the canon 24 70.

the camerea is 3od.

i have down loaded to computer and magnified to 400% some sharp others not at all lengths, so is this a lens problem or am i doing something completly idiotic.

(sorry did say quick question)

cheers ERic
 
I have one for my D700 and it has an issue when using the focus assist on the SB900 attached to camera. This is a known issue and Sigma have asked me to return the lens so they can update the chip with a fix from Japan.

However, this is only with the flash assist, if I use the cameras focus assist then it works fine, in fact it focuses alot quicker than using the flashes one!!.

Also, this problem was at ALL focal lengths and would back focus by quite alot.

I haven't sent it back yet but I probably will at some point in the next couple of weeks. To be honest it is not a biggie for me, but if I want to sell the 24-70 in the future I can say it has been 'fixed'.
 
cheers will try that now see if it is any different.
will post again in a minute.
 
just tried it out i think it is the lens shot at 60 with camera flash and f4.0 sharo at 68 and below 70 mm not at all some very oof and others nearly there.
will take back i think.
 
There have been quality issues with Sigma, and this lens seem to suffer more than some of the others. I know that the AF on mine is not good on macro, I usually end up resorting to Live View and manual focus.

Other than that, it's a superb lens, it's a shame that the quality standard at Sigma lets it down.

Steve
 
Does the 17-70 f2.8 have the same issues?
 
:help: Gosh, this was my next purchase (and possibly later today as they have em on sale at Jessops) - is there anyway I could tell in the shop if there was a problem, before taking it out of the door?
 
Magnified to 400%? Why? I doubt any picture will look too good zoomed that far in! Sounds a bit like it could be a DoF (Depth of Field) problem. Close up and wide open, your DoF will be very shallow, so any slight (even a couple of milimetres) movement could cause poor focussing.

Just done a quick test series at 70mm, close focus and a selection of apertures at full stop intervals. At f/2.8 and 400%(!) there is a little softness but by f/4 (and at a reasonable screen magnification, 100%) my eyes are almost bleeding! It's probably worth noting that I had the camera held down on the table and was shooting text which will show up any slight softness. Not got anyone here to try to replicate the OP's shoot.
 
I want to add to my original post about the focus issue with flash, the actual lens and the IQ is very good. At f2.8 it is a little soft but nothing a bit of USM won't sort out in Photoshop. f3.2 onwards is excellent on my copy.
 
V8burble said:
You know the 17-70 is not a constant max f/2.8 don't you btw Andy?
Click to expand...
If i knew what you were talking about i could give you an answer! :D:D:D

Sorry but i know very little about all this photography lark still!!
 
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