Question about F-stops in Consumer Digicam

I recently purchased "The Underwater Photographer, 3rd edition" by Martin Edge (Alex Mustard wrote an extensive review). Indeed a very valuable and easy to understand book. I have only been cross-reading it sofar, so maybe the answer to my question is in the book itself lol. I aks the question anyway.

On page 214 Martin Edge describes an Excercise:"Sunburst". He mentions "If you are using a digital compact your smallest aperture is around f8, which is closely equivalent to f22 on an SLR".

Apparently apertures in SLR range from f22 to f2.5 (or thereabouts).

My Oly c5050z ranges from f8 to f1.8.

I just checked the range on my compact: f8.0 - f7.0 - f6.3 - f5.6 - f5.0 - f4.5 - f4.0 - f3.6 - f3.2 - f2.8 - f2.6 - f2.3 - f2.0 - f1.8 (with the lens in wide angle position, widest aperture in tele is f2.6).

As you see these f-stops do not have the correlation as in a SLR where the next f-stop is the latter multiplied by +/-1.4 (square root of 2) e.g. f4 x 1.4= f5.6, f5.6 x 1.4= f8, etc. (Each next f-stop halves the aperture surface) (see dpreview)

Is there a way to find out which f-stop on a digital compact corresponds to its equivalent on an SLR? Is it just as simple as putting that the widest and smallest apertures on compacts and SLR correspond with one another and all the values in between as well? Or are there more conversion factors I should take in acount?

In other words some kind of "conversion table".

Would be interesting as most of the book is focused on the use of (d)SLR.

Thanks and Happy New Year to you all,

Bart

Assuming DOF is your main concern, this may be a start:

http://www.dofmaster.com/dofjs.html

DOF is often quite subjective anyway, but this may get you started.

At the wide open apertures on a digicam, you are still getting far more depth of field, than at wide open on an SLR. This is one of the main limitations of P&S digicams - lack of ability to get shallow DOF.

A digicam at f8 in macro mode still has far more DOF than an SLR at f8, but probably not as much as f32...

The intermediate values between the traditional F8, F5.6, F4, etc are 1/3 stops which are actually quite common on digital cameras, and allow a finer transition in aperture sizes. On some SLR models, you can reduce the number of steps by changing the steps to 1/2 or 1 stop, instead of 1/3 stop, for quicker adjustments.

As for equivalent F-stops between digicams and SLRs, there's no such thing. I have not yet read the latest version of Martin's book, but I assume he meant that the actual size of the diaphragm was similar in the situations you describe. Quick example:

- For a digicam at its widest real aperture of say 8mm at F8, the size of the diaphragm is 1mm (8/8 = 1mm)

- For a SLR with a 20mm lens at F22, the size of the diaphragm is also about 1mm (20/22 = 0.9mm)

Thanks Matt.