Other collecting activities?

From: Tony Duell <ard_at_p850ug1.demon.co.uk>
Date: Tue Apr 20 18:03:36 2004

>
> On Apr 19, 23:36, Tony Duell wrote:
>
> > I didn;t say that digital cameras have no uses, just that I have no
> use
> > for one. I take almost entirely static subjects, and I want high
> > resolution (to be honest 3.1 M pixels is worse than 35mm (I estimate
> that
> > as being about 12M pixles), let alone medium or large format).
>
> Hi-res 35mm is probably better than that. Kodachrome certainly is; it
> can resolve a couple of thousand lines per *millimeter* under ideal

I was assuming a resolution of 100 lines/mm (good lens, good film), I
wasn't just considering the resolution of the film (after all, I use said
film in a camera, and it's the end result that matters).


> conditions. Even fairly conventional fine-grain black-and-white films
> have been able to manage 1000 lines per mm since the 1940s. That means
> if you take the full height of a 35mm image, and enough of the width to
> match the typical aspect ratio of a digital camera (lets say 3:4), the
> image could resolve the equivalent of 24000 x 32000 = 768M pixels!

Ouch!. I hate to think what a 5*4 sheet film is equivalent to.

>
> It's not quite as simple or dramatic as that, of course. It's not just
> the resolving power of the film that affects the image quality, there
> are irradiation and halation effects to consider, as well as
> graininess, lens quality ("the diameter of the circle of confusion" is
> a phrase I will never forget). On the other hand, there are digital
> artefacts like edge effects to think about too.

And noise in the electronic chain under low light conditions (which to me
looks worse than the grain on fast conventional film).

>
> Even if you take a normal fine-grain silver halide image, under average
> conditions, you'd have about 15M pixels (I found that in a few
> references on the web). That's about 5 times more than a 3.1M pixel
> digital image -- except they're analogue pixels, in a sense; the size
> and colour are infinitely variable, not variable in discrete steps.
> Moreover, 3.1M pixels in the camera aren't 3.1M pixels in the final
> image. It depends how they're used, but in the camera, you typically
> need three pixels, one for each of R, G, and B, to get one RGB pixel in
> the image. Some techniques use even more (the Bayer algorithm uses 4).

Argh!. You mean they fiddle the figures? I'd assumed that a 'pixel' was
an RGB triad, not a third of one. So you mean you may only get 1 million
points in the image from a 3.1M pixel camera?

-tony
Received on Tue Apr 20 2004 - 18:03:36 BST