At 12/31/2021 04:00 PM, Mike wrote:
>Nothing says Happy New Year like some serious pixel peeping.
>
>This Sigie lens has to be sharp in the corners wide open for astro landscapes.
> Sigma has quite good QA now but on FM about 1/3 end up being sent back. I
>was tempted by the sonnie 14/1.8 but there are more aberrations in the corners
>even at f2.8, the corners are just so-so at 1.8 and the copy variation is
>quite large. It is smaller and lighter and thus better for travel though.
>
>I focused on our chimney in the center of frame and then moved the cam so the
>chimney was in each extreme corner--200% crops. IBIS off and on tripod. These
>are SOOC jpegs.
>
>https://www.olyendomike.com/Sigma-14-24-f28-centering-200/
>
>I think modestly soft at 24mm in the rt lower corner but not badly decentered
>at 200%. Good enough or not??? I can send it back for 30 days.
>
>Mike
I was curious. At 24mm the horizontal FOV is around 74 degrees. If you were to
focus at center then shift to the side, you would have to move back about 25%
to put the chimney back in the plane of focus. At long distances the COC
(circle of confusion) eats the difference.
Cos(34) = Adj/Hyp where Adj is the center distance and Hyp is the left/right
distance.
Say you are 50m from the chimney, then you would have to move back another 12m
to keep the chimney in the center focused plane of focus.
Hyp = 50m/Cos(34) = 62.6m.
For corners use FOV 84/2 (42) degrees. 50m/cos(42) = 67.3m
nit-picky WayneS
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