Taking photos of displays...
bv at norbionics.com
Sat Mar 5 04:59:31 CST 2005
On Wed, 02 Mar 2005 00:27:12 +0100, Tony Duell <ard at p850ug1.demon.co.uk>
>> Unless, of course, you actually have a decent digital camera... ;-)
> Yes, but I can;'t afford a 5*4" digital back for my monorail. And even
> then I am told film still has a higher resolution.
>> It's a big picture - 3028x2002 pixels (native resolution of my Nikon
>> D70) -
> I hate to tell you this, but a good 35mm image is normally regarded as
> being equivalent to 12--20 megapixels. 6 megapixels is not enough IMHO.
The limit for precision-developed high quality B&W film exposed within a
quarter stop of the optimum with the best Leica lenses is almost 100 lines
Lens resolution needs to be about 3x film resolution in order to get
almost the full theoretical resolution out of the film.
One line pair is somewhat the equivalent of two pixels. That gives a
4800∗7200 pixels, each of which needs to be 16 bits deep for B&W. Ordinary
film with normal treatment can be scanned at half that linear resolution
without any loss. I scan my 35mm colour slides in archival quality with a
file size of 50-60MB per image at 48 bits per pixel with lossless
Larger formats have a lower linear resolution, smaller ones higher
resolution. This is because smaller lenses are more perfect - closer to be
diffraction limited. I have made some really nice 18*25cm enlargements
from Minox negatives (9*11 mm), Minox lenses are a lot better than the
best lenses for 35mm cameras, but not nearly so much better that it
compensates for the size difference.
The same applies when you go up from 35mm to 60 or 70mm, or from there to
a studio camera.
I think I would scan an 18*24cm negative at 9000*12000, which would fill
up even modern disk drives rather quickly.
If you want to take a picture of a display, there is not much use of
having more than four times the resolution of what you want to photograph,
twice the resolution is just about sufficient. The D70 should be able to
make top-quality screenshots of displays with up to 1500*1000 pixels. Few
historical displays have better resolution than that, but vector displays
are difficult. They have extremely high resolution and are very dim. IBM
had some character displays where each character was made by shaping the
electron beam through a steel stencil. They would probably also need a
very high resolution camera to get a "perfect" screenshot - I never tried,
but I have a suspicion that something bigger than 35mm would be useful.
A nice sheet of black velvet is very handy if you want to take pictures of
displays, there are always some control lanps to give reflections even in
a darkened computer room.
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