Quote:
Originally Posted by roughy
Whilst there are quite a few tools to calculate the difference in FoV, is there a formula to calculate the percentage difference in brightness between these to focal ratios?
Sensors that will be used are KAF8300 (5.4 microns) and MN34230 (3.8 microns).
Thanks
Mark
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Hi Mark,
Yes, it has to do with the way the f-Number is defined and the increase in light per unit area/field, but by way of a worked example:
in your question of an f/7 vs f/6.5 optic, the f/6.5 would be ~16% brighter.
(7/6.5)^2 = 1.15978
In other words the f/6.5 optic is 1.15978 times (~16%) brighter than the the f/7 optic.
Or if you prefer,
if the f/7 brightness were 100 units, then the f/6.5 brightness would be 115.978 units or ~ 16% brighter.
Best
JA
Also note that if the image circle differs between the 2 optics the considerations are more complicated, especially if there is any vignetting.