Okay! Let's try to make this crystal clear. Manufacturers of digicams, more often than not, give us a 35mm equivalent for focal length because that's what so many of us are used to, but they neglect to give us a DoF equivalent
I don't know why this is. I can only assume it's because DoF is considered to be more esoteric than focal length and most buyers of P&S digicams wouldn't have a clue what DoF means.
On the other hand, to be fair
, it might be because the aspect ratio of the 2/3rds format is different from 35mm, so the 35mm DoF equivalent is not one easily defined figure. It depends on where you've positioned yourself at the time the photo is taken. Are you cropping the 4:3 format of the F828 to equal the 3:2 format of 35mm, or not? Do you want that extra horizontal expanse or not? If you don't, you can get closer to the subject, or use a slightly greater focal length setting on your zoom, and that affects the DoF.
Either way, the DoF equivalent at any given aperture is significantly greater for the smaller format. For equal horizontal FoV it's about 4 F stops, and for equal vertical FoV it's about 3 1/2 F stops, in the case of the 2/3rds format versus 35mm.
I'll use the greater figure for ease of calculation. I'm using a 200mm lens on my 35mm camera and I'm shooting a scene with some interesting stuff in the foreground which I want to be sharp. My lens is likely to be sharpest at f8, very nearly as sharp at f11, a bit off at f16 and decidedly fuzzy at f22.
I have a problem deciding whether or not to use f11 or f16. I know I'm going to blow up this photo to A3+ so I decide to use f11 and the hyperfocal distance principle (bring focussing back slightly from infinity), but I also know that F11 is not going to give me sufficient DoF to get everything sharp that I want to be sharp. I'm between a rock and a hard place.
But hey! Maybe there's a solution. I pull out the F828 from my bag. This lens is sharpest at F5.6, equivalent to f22 on my 35mm camera. Wow!
Maybe the F828 lens is also equally sharp at f8. That's equivalent to f32 on my 35mm camera. Extra wow!
On the other hand, maybe the performance of this Zeiss lens really sucks at f8. I just don't know. The dpreview foil test gives the impression that resolution is actuall better at f8, but I find this difficult to believe.
So, I'm hoping some of you brave owners of the F828 will risk personal trauma and do a few experiments at various apertures and let me know what the results are. I know it's a lot to ask. If you discover that performance at f8 is really lousy, this could make you angry and depressed for days. It's a great risk, but in the greater interest of scientific objectivity, which we can all benefit from, I hope at least some of you will oblige.