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DPChallenge Forums >> Tips, Tricks, and Q&A >> ? about lenses
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03/26/2015 10:34:26 AM · #1
I have a Sigma 70-200 1:2.8II and a Tamron 28-300 1:3.5 If I take a picture at 200mm with both lenses, the 200 is soft around the edges. The 300 is not. Is that normal? Or is the something wrong with my lens?
03/26/2015 10:41:53 AM · #2
I don't have direct experience with that particular 70-200, but it may well be normal behavior if you are shooting wide open (at f/2.8). I am a little surprised, however, that you'd be seeing corner softness using an APS-C body.
One thing to check out is whether you have a problem with focus error. That lens apparently had a reputation for focus offsets.
03/26/2015 10:55:22 AM · #3
I didn't explain my self very well, (which is normal for me) I took a picture of a cloths pin on my cloths line at about 5ft. The 200 was soft around the edges of the cloths pin but the 300 was not.
03/26/2015 11:00:40 AM · #4
Originally posted by meow:

I didn't explain my self very well, (which is normal for me) I took a picture of a cloths pin on my cloths line at about 5ft. The 200 was soft around the edges of the cloths pin but the 300 was not.


I'm sure a few pictures would help.

My guess is that this is due to a few factors. First, the 200 is at the extreme of it's range @ 200mm, while the 300 is in the middle of it's range, this is likely to have at least some effect.

Secondly, it may well just be a camera/lens combo - each lens is adjusted to within 'tolerance' which may, or may not, align well with your camera's adjustment, which is also within 'tolerance'. So this means the tolerance might be -7 to +7, so if you have a camera that is -5, the -7, -6, -5, -4, -3, -2, -1, 0 lenses might be great, while anything above that tolerance would be too far off. This is a common issue with ILC systems, and the only solution is to have the factory (or service center) adjust your body and lenses to work together.

Finally, it could just be an optical element out of whack, or the fact that you're focusing VERY closely, where the lens is certainly far from optimally adjusted. These lenses are meant for long distance work, so at 5ft, who knows what's going on.
03/26/2015 11:13:11 AM · #5
Many zoom lenses can go "soft" at the extreme, so what you're seeing here is not exactly unusual - particularly if you're shooting wide open. Zooms will have a sweet spot, and I would expect a 28-300mm to be sharp in the middle range. At the same time I am thinking that stopping the 70-200mm down to f8 to f11, if you're shooting wide open, will improve on the softness.
03/27/2015 07:28:33 PM · #6
Thank you all. I think it was more me than the lenses!
03/27/2015 10:20:56 PM · #7
At 200mm and f2.8, you may be getting the softness from the shallow depth of field, and curvature of field. If you are perpendicular to the clothes line, the field curvature may have something to do with the softness.
With most ordinary lenses, the focus is not a flat plane, but rather a curve, sort of like the inside of a ball, so the pin may be in focus, but the line near the edges of the frame out of focus.
Most dedicated "macro" lenses have a flat field lens formula and focus in a flat plane.
You can also try manual focus to see if the focus problem is actually with the lens/ camera combination.
Try shooting the test again using aperture priority, and set both lenses at the same aperture to see if it changes the way the 200mm lens images look.
It helps to use a tripod when doing comparisons and testing if you have one.

Maybe the actual clothes line is fuzzy.

03/28/2015 09:59:38 AM · #8
Originally posted by MelonMusketeer:

Maybe the actual clothes line is fuzzy.

OMG what a DPC response! LOL!!! Love it!
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