digital cameras

From: Philip.Belben_at_pgen.com <(Philip.Belben_at_pgen.com)>
Date: Thu Jul 15 12:05:58 1999

>> Now compare that with the 330 lines per mm you get from a typical
>> apo-lanthar or apo-tessar as were made back in the '30's . . .
>
> Indeed. As several of us commented last night, a reasonable 35mm SLR will
> give you 100 lines per mm. Medium format (or large format) will do a lot
> better, of course.


Of course? I don't understand the "of course". I see no fundamental reason why
a larger format will give you a greater resolution _per mm_. In fact, I would
think that the wider viewing angle for the same focal length would mean that you
might get less resolution.

The big advantage as I see it of larger formats is that for the same resolution
per mm you get much more detail in the frame!

I use medium format - I got a Yashica TLR (Rollei clone) for 6 pounds at a
charity auction a few years ago, and it got me hooked on it. Recently I damaged
my Yashica, so I've just bought a Hasselblad (a good set of accessories is
looking rather pricey, though). I'd love to find an 16384*16384 or similar
digital back at an affordable price! Heck, if I saw a 4096 * 4096 digital back
for my 'Blad below 500 pounds I'd probably buy it, even though that's only 36
lines per mm!


>> I guess most people are used to the unsharp pictures that come from the
>> average point-n-shoot, with film processed by one of the 'photos back in
>> an hour' places. Digial cameras might well produce results similar to
>> those. But that doesn't mean you can't do a lot better with film (or
>> indeed with a digital camera given a decent CCD (=$$$$$$$$$$))


I think there are two independent viewpoints here. If you are taking pictures
for display on people's computer monitors (e.g. on web sites) you don't need
more than a few lines per mm, since the monitor itself will probably only
display 3 or 4 pixels per mm (say 2 lines). A 640 * 480 pixel picture is the
largest that will display on many people's screens. For this purpose a digital
camera of say 1280 * 1024 is probably perfectly adequate.

If you're taking pictures to blow up to a foot or two across and print on high
quality paper, then most digital cameras are quite inadequate, and a large or
medium format or really good 35mm film camera is required.


>> >If you have a 100mm wide print (normal sort of size) and 640 pixels,
>> >that's only 3 or 6 lpm (depending on whether you think a line is 1 pixel
>> >or 2). That's not a poor resolution, it's a non-existant resolution!
>> >
>> >Ouch!. Now I know why I can't stand those digital cameras.


Tony, when you talk about 640 pixels across a 4 inch print being only 6 pixels /
3 lines per mm, you've just stopped looking at film resolution and started
looking at print resolution. Don't forget that the standard 35mm negative is
generally considered blowable up to as much as 12*8 inches, so 100 lines per mm
at the film becomes 12 lines per mm at the print; 3 lines per mm at the print
corresponds to 25 per mm at the film. So it is poor resolution, but not the
"nonexistent" resolution you were talking about.

On the subject of lines per mm, what is the resolution of a typical ccd per mm
_at the surface of the chip_?


Philip.

PS why do people so often talk about blowing 35mm up to 10*8 or 12*10 as the
limit? Is it simply standard paper sizes? It's certainly not the aspect ratio
of the negative.
Received on Thu Jul 15 1999 - 12:05:58 BST