bryan conner
Unregistered
Because of a recent problem with one of my lenses, I have been analyzing (probably over analyzing) the sharpness of my lenses. The one lens I have sent in for service definitely had a focus issue....probably due to it bouncing off of the concrete after falling from my camera bag when I tripped <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/rolleyes.gif' class='bbc_emoticon' alt='
' />. I am satisfied with two of my other lenses' performance, but my Sigma 15-30mm has gotten my attention. I very rarely use this lens as I have never been really happy with it's sharpness.
How can I easily determine what level of sharpness is acceptable for this lens and when it should be sent in for adjustment? I use it on a Canon 40D and the images do not look sharp at all away from the center. Is there a reliable at home test? I want to either verify that the lens is overly soft or that I am overly paranoid! <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/tongue.gif' class='bbc_emoticon' alt='
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bryan conner
Unregistered
Thanks Arv. My lens has never been that good in my opinion. Of course, looking at a print of an image or even the image on a screen and deeming the corners to be excellent is subjective. The confusing part is that the lens gets such bad reviews from users on a wide variety of web pages and forums....but it also gets good reviews on some sites also. I do not want to expect too much out of the lens if the quality will never be there. I purchased it used several years ago and I got a good deal on it.
I would really like to have a method of making a fair determination of the focus performance of the lens. Should I photograph a newspaper (or something similar) attached to a wall to judge the performance? Or, is there a better method? I want the test to be as fair and as accurate as possible before I go through the process of sending it in to Sigma.
anyscreenamewilldo
Unregistered
[quote name='Bryan Conner' timestamp='1305480013' post='8336']
Because of a recent problem with one of my lenses, I have been analyzing the sharpness of my lenses. . . . How can I easily determine what level of sharpness is acceptable. . . and when it should be sent in for adjustment? . . .
[/quote]
- well if you want a cheap check on how your lenses compare you can download a an iso12233 test chart from this site - [url="http://www.graphics.cornell.edu/~westin/misc/res-chart.html"]http://www.graphics..../res-chart.html[/url] -
it should print out A1 size at useful sharpness quality for a few dollars (except the blacks will be grey) - shoot it, pan it for the sides etc, to check the lens against a good lens -
not the super PZ test the guys here do, but useful for checking if what you've bought is what you hoped it would be -
. . . or you can buy a good quality, and more expensive, chart from imatest and other places
[quote name='Bryan Conner' timestamp='1305578379' post='8380']
I would really like to have a method of making a fair determination of the focus performance of the lens. Should I photograph a newspaper (or something similar) attached to a wall to judge the performance? Or, is there a better method? I want the test to be as fair and as accurate as possible before I go through the process of sending it in to Sigma.
[/quote]
The procedure is described here in FAQ section. Also at BobAtkins.com are some hints (testing camera lenses). I think it is more valuable to test decentering or select the best copy if you have few, but to determine is the sharpness within specs by eye is really difficult. You can compare to another lens, but the results (better or worse) you may already know.
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bryan conner
Unregistered
Thanks Arv and anyscreenamewilldo, I had previously browsed through the lens test FAQ, but failed to notice the instructions for self testing of a lens. Wonderful information there. I plan to do this today. I appreciate your help.
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