Is there a way of testing for softness?
- Thread starter vecsri
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The main thing to do is eliminate all chance of camera movement by using a tripod and remote release or self timer. If you're photographing newspaper make sure it's lined up squarely with the camera. You can also use a brick wall where the texture of the bricks and lines of mortar show good detail. Focus manually so you can get it spot on, and take a few shots at different apertures. Again make sure the camera is square with the wall
Set up everything very carefully or the test will be pretty meaningless.
Set up everything very carefully or the test will be pretty meaningless.
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I don't see a great deal wrong there, assuming these are unsharpened images. The only questionable result is wide open at f2.8, but when you look closely, it's acceptably sharp at bottom right but way soft at top left which I suspect is down to everything not being lined up exactly square, which is difficult anyway, and the very narrow DOF at f2.8 is unforgiving of errors in lining up.
As you'd expect, things improve as you stop down and DOF increases.
Another quick test you can try wide open at f2.8 is to photograph your keyboard from a low angle, but just manually focus on one letter which should be the only sharp one if all is well. Again use a tripod and release, but you don't have to worry about squaring things up and this method ensures the image is sharp at the point where you focus.
I'd do that last test to satisfy yourself, but I honestly doubt much is wrong.
As you'd expect, things improve as you stop down and DOF increases.
Another quick test you can try wide open at f2.8 is to photograph your keyboard from a low angle, but just manually focus on one letter which should be the only sharp one if all is well. Again use a tripod and release, but you don't have to worry about squaring things up and this method ensures the image is sharp at the point where you focus.
I'd do that last test to satisfy yourself, but I honestly doubt much is wrong.
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LOL. Seriously - getting sharp pics is mostly down to common sense and good technique in hand holding or use a tripod. I always use a tripod where it's practical to do so.
At 70mm the minimum safe hand holding speed would be 1/70 of a second, but people's abilities vary from one to another and it's always safer to go faster anyway if you can.
At 70mm the minimum safe hand holding speed would be 1/70 of a second, but people's abilities vary from one to another and it's always safer to go faster anyway if you can.
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Appears to be "normal"
The review I read states that this lens is not useable a t 70mm/2.8
"The Sigma 24-70mm f/2.8 EX DG Lens is sharpest at the wide end of its focal length range. At 24/28mm, the 24-70 is very sharp in the center at f/3.2. However, performance gets progressively worse as the focal length is increased. To me, 70mm f/2.8 is not usable on this lens"
From http://www.the-digital-picture.com/Reviews/Sigma-24-70mm-F-2.8-EX-DG-Lens-Review.aspx
Bob
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There you go - what Bob said.
It's not uncommon for lenses to be soft wide open, and even the very best lenses whilst more usable wide open, benefit from being stopped down a little. Don't bin the lens unless it's really important to able to operate at f2.8 - which it is for me.
You get what you pay for with lenses - expensive game!
It's not uncommon for lenses to be soft wide open, and even the very best lenses whilst more usable wide open, benefit from being stopped down a little. Don't bin the lens unless it's really important to able to operate at f2.8 - which it is for me.
You get what you pay for with lenses - expensive game!
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I think reviews fall into two distinct categories....consumer reviews found on site like Amazon and Ebay and "professional" reviews found on photography sites.
The former are written by well meaning amateurs who have just paid a lot of money for something, found that it's better than their previous version, and hence say the usual good things (in general)
The "professional" reviews tend to tell it like it is...real pro's and con's stuff. There are about 6 or 7 mainstream ones and it's not too often that they'll disagree.
For your lens, the constant f/2.8 is a purely mechanical description and does not factor in whether it can be used (acceptably) through the whole range.
I have a 50/1.2 lens that is wonderful except when used between 1 and 1.5 metres at f/1.8-f/2.8...then it has a marked focus shift that inhibits its useage....a well documented problem. I was aware of the issue before I bought it and so there's no disappointment on my part.
The moral is read, read some more and then try (if possible) before buying.
Bob
The former are written by well meaning amateurs who have just paid a lot of money for something, found that it's better than their previous version, and hence say the usual good things (in general)
The "professional" reviews tend to tell it like it is...real pro's and con's stuff. There are about 6 or 7 mainstream ones and it's not too often that they'll disagree.
For your lens, the constant f/2.8 is a purely mechanical description and does not factor in whether it can be used (acceptably) through the whole range.
I have a 50/1.2 lens that is wonderful except when used between 1 and 1.5 metres at f/1.8-f/2.8...then it has a marked focus shift that inhibits its useage....a well documented problem. I was aware of the issue before I bought it and so there's no disappointment on my part.
The moral is read, read some more and then try (if possible) before buying.
Bob
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I think it's preferable to to see the image straight from the camera when assessing lens performance and assess whether the image should then sharpen acceptably. Clearly, all vecsri's shots will sharpen nicely with the exception of the 2.8 shot, but that shot obviously isn't lined up squarely anyway and the lens is probably better than that shot would have us believe.
Alistair
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Try this : http://www.focustestchart.com/
spencer
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I had a softness issue with my first Sigma 24-70 f/2.5 EX DG macro, there are some posts on it, in the end I sent it back to warehouse express & received a replacement two days later!
The replacement was much better, but still slightly soft.
Hope that helps?
Spence
If you live near me you can always pop down & try it with my Sigma?
The replacement was much better, but still slightly soft.
Hope that helps?
Spence
If you live near me you can always pop down & try it with my Sigma?
Thanks for the offer thought bud!