Re: [OM] Keeper--yes, no, or can't tell?

[Wayne Shumaker]

At 4/2/2023 01:55 PM, you wrote:


>Will be using this lens wide open or nearly so for astro in a couple weeks so 
>made another exchange with B&H to try and get a sharp/centered copy. A target 
>is fine but my chimney is easy and readily available and good enough to check 
>for even sharpness in corners at infinity.  
>
>Third copy seems pretty well centered based on corner sharpness:
>
>https://www.olyendomike.com/Third-copy-Sigma-2014/
>
>I am not sure it is as sharp in the center and left side as the second copy 
>but the testing conditions were different. The chimney was heavily backlit 
>both times but more severe with the third copy and that might washout some 
>contrast which can give the impression of poorer resolution. I put the center 
>images in separate tabs in my browser and went back and forth. All the images 
>are cropped SOOC jpegs so processing is the same.
>
>Center comparison at F2.8:
>
>https://www.olyendomike.com/Third-copy-Sigma-2014/i-jhLFXnx/A
>https://www.olyendomike.com/Second-copy-Sigma-20mm-f14-DGDN/i-BsZDLg4/A
>
>Right Lower Corner at 200% second copy vs third copy:
>
>https://www.olyendomike.com/Second-copy-Sigma-20mm-f14-DGDN/i-3Mhh8FV/A
>
>https://www.olyendomike.com/Third-copy-Sigma-2014/i-MttBpJ7/A
>
>Perhaps I'll repeat a couple shots w/o the backlight and be sure the center is 
>as good on the current third copy as the second. B&H closes for Passover soon 
>so have to decide quickly. The Center F2.8 comparison bothers me, though the 
>lighting differences may negate a valid comparison.  Dustin Abbott's 
>comparisons at different apertures showed the contrast is nearly as good at 
>F1.4 and maxes out near F2.8.  The sharpness improvement at F2.8 vs 1.4 was 
>dramatic in my testing of all 3 copies.  I'd rather have a bit sharper copy in 
>the center that was mildly decentered.  
>
>My Sigma 14-24/2.8 is very sharp at F2.8 especially at 14mm.
>
>Pixel peepers and any other comments welcome, Mike

An interesting article still relevant today I think? before dpreview disappears

https://www.dpreview.com/articles/7333489584/variation-facts-and-fallacies

WayneS
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