f numbers - life would much simpler

Started Apr 12, 2012 | Discussions thread
Andy Crowe
Senior MemberPosts: 1,550Gear list
F-number corresponds to exposure
In reply to Louis_Dobson, Apr 12, 2012

But what would you use the aperture entry pupil diameter for?

The idea with f-stops is the f-number relates directly to the exposure, so a 1/60 sec exposure at f4 on a 14mm lens will be the same (minus any transmission loss) as f4 on a 100mm lens, despite having completely different physical aperture sizes.

This seems more useful than the physical aperture size.

When you are buying a lens and figuring out if you want to pay for it, what you want is the actual aperture, or the entry pupil, if you prefer.

S0 a 75mm f1.8 becomes a 75:42mm.

Or a 25mm f1.4 becomes a 25:18mm

Once people had got used to it, it would be much, MUCH more meaningful.

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