Taking photos of displays...

Bjørn 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>  
wrote:

>> 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.
>
>>
>> http://www.30below.com/~zmerch/d70/Nitetime_shot_30sec.jpg
>>
>> 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  
per mm.

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  
compression.

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.


-- 
-bv



More information about the cctalk mailing list