Would Like To Verify Exposure Duration

Started 4 months ago | Questions thread
Iliah Borg Forum Pro • Posts: 28,241
Re: Exposure nominal and precise
2

Bernard Delley wrote:

Iliah Borg wrote:

Bernard Delley wrote:

BTW, apertures (except at fully open aperture) obey N = 2^(p/6) with p an integer.

p/12 and p/24 for Nikon, depending on the body and the lens.

interesting ! please explain.

Current lens control protocol is based on p/24. To set the aperture on a lens, a 1-byte value is to be sent, f-number = 2^(value/24).

Just verified my D850 menus, and find steps for exposure control and ISO step options:

step value 1/3

step value 1/2

(and step value 1)

using step value 1/3 and the fact that apertures go by the square root of area, I came to p/6.

I must admit that, if you combine the two menu settings, then finer exposure steps are sometimes possible, like

q = 0 , 1/3 , 1/2 , 2/3 , 1. or nominal apertures like f/4 , 4.5 , 4.8 , 5 , 5.6 ...

this implies indeed aperture steps p/12 . However p=1 , 5 , 7 , 11 are not available. I see no way to set nominal f/4.2 , f/5.3 f/6 f/7.6

Of course manual lenses can provide continuous control of aperture. But, the accuracy of setting is not supportive for such fine control with the lenses I have seen.

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