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pdmoylan
31-Jan-2011, 12:54
I wonder if anyone can offer a solution to calculate the increase of coverage at F32/f45 etc as a percent or in real mm terms when the f22 coverage is known. Nikon literature indicates coverage wide open and at f22. Can we deduce that the increase for each f stop is linear? If this is the case then the Nikkor 210W at F45 would have just enough image circle for 8x10 without movements.

Dan Fromm
31-Jan-2011, 13:59
Why speculate and ask others to speculate when you can ask the lens?

Jim Galli
31-Jan-2011, 14:07
Unless the design is perfectly symmetrical there usually is zero gain. Rather, Nikon stopped at f22 because diffraction loss is a trade off that their target audience would probably never consider.

Mark Sawyer
31-Jan-2011, 14:33
It has to do with where the decreasing size of the stop eliminates the mechanical vignetting by the barrel, which varies from design to design, even within a family of lenses. And keep in mind this is only for "illumination", not an acceptably sharp and useable image circle. So no, there's no set formula for all lenses.

pdmoylan
31-Jan-2011, 19:22
Thanks all. Next step is experimentation.