f-stops shutter-stops

[vvizard]

Exactly how big is a _FULL_ fstop? If what I've understood (at least thinking I have) is right, 1.0 -> 2.0 is not a full fstop (it's more). Is an fstop increasing linearly when the f's increase? If so, how much?

And what for shutter-stops. I've read that IS will give the effect of two(?) full shutter-speeds faster than normal. How much faster is one shutter-stop?

[defordphoto]

Heheh....All the years I have been shooting and I can't answer that question. I am so glad I never became a measurebator.

Anyway, I did find this: http://www.uscoles.com/fstop.htm

Probably waaay more information than you ever wanted to know baout f-stops, but there ya go.

[Tom W]

RFM - good reference site!

I will note that F-stop numbers follow a certain pattern. F-1 is the square root of 1. F-1.4 is the square root of 2. F-2.0 is the square root of 4, and F-2.8 is the square root of 16. If you follow on up, the F-stop numbers follow the same pattern (though rounded off to the nearest 1/10th up to F-10 and the nearest whole number after that. So you have f-stops that equal the square roots of 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, etc. It all fits in with the amount of lite that the aperture lets in. There's some higher math involved, but we don't need to go there (not that I could anyway, but its there somewhere).

EDIT: I have to add, when you have a given exposure, say, F-8 at 1/125 second exposure and you wish to double the shutter speed to 1/250 to stop certain action, you will have to open the aperture by one stop to F-5.6 to obtain the same exposure on your film or sensor. Well, interestingly, you will open the aperture from the square root of 64 (or F-8 ) to the square root of 32 (or F-5.6 ), so as you double the shutter speed, you half the square of the F-stop.

This is probably overcomplicating the whole issue.

[vvizard]

Yeah thanks for the site. This really helped me a lot. I understand it now :)

[defordphoto]

Coolness! Glad I could help. Guess I should read that site too eh?

[karusel]

Extremely educative link!

[horqua]

Do a Google search on the Inverse Square Law.