View Full Version : Lens Image Circle Calculation

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.

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