RE: [APML] SFL and Flats Was: Fuji Provia 400F and exposure time

["Lane, Jason R" <jason.lane@navy.mil>]

P.S.

Just was thinking that for a film like Kodak Tech Pan with such a very small grain structure, the S/N may be limited by dark current and so you wouldn't get the full benefit of the film.  It depends on if you can detect the grain structure of Tech Pan in a scanned image.  If you can, then I'd say all is good.  I don't use Tech Pan so I don't have any to scan in and look at.  What I've also wondered is how many scans are required to ensure that the temporal noise from the scanner has been removed from the averaged image altogether.  This could be checked by averaging progessively more images.

-Jason

-----Original Message-----
From: astro-photo-bounces@seds.org
[mailto:astro-photo-bounces@seds.org]On Behalf Of Lane, Jason R
Sent: Wednesday, July 07, 2004 1:40 PM
To: Discussion of Film Astrophotography
Subject: RE: [APML] SFL and Flats Was: Fuji Provia 400F and exposure
time


Hi Wei-Hao,

That's a good question.  I would guess that it probably only affects the LSB of the pixel data, but I'd have to look at the imager specs to know for sure (I can't think off-hand of a good way to measure it independently without breaking the light source inside the scanner).   What I do know is that I can scan in a slide and look at the grain structure of the film in the scanned image.  If we call the actual grain structure of the film the "noise", then scanner dark current is not as strong as the noise of the film.  Temporal noise, however, can definitely be significant, which is why averaging several scans is so helpful.  I started doing this with the slides from my last roll of film and the benefit is noticeable.

-Jason
 

-----Original Message-----
From: astro-photo-bounces@seds.org
[mailto:astro-photo-bounces@seds.org]On Behalf Of Wei-Hao Wang
Sent: Wednesday, July 07, 2004 1:10 PM
To: Discussion of Film Astrophotography
Subject: Re: [APML] SFL and Flats Was: Fuji Provia 400F and exposure
time


Hi Jason,

You are right.  I totally forgot there is dark current.
How strong do you think it is?  Can it be stronger than the noise
on the film?

Wei-Hao
 

On Wed, 7 Jul 2004 07:24:43 -0700, Lane, Jason R <jason.lane@navy.mil> wrote:
> Hi Wei-Hao,
> 
> Unless we're thinking about two unrelated things here, scanning a slide multiple times and averaging the results won't give infinitely high scanning S/N.  The S/N will be finite, with the Noise defined by the average value of the usual temporal-independent noise (I'm thinking mostly dark current here).  This will give a consistent scanner noise value across the slide (ie minimal variation), but it won't be 0.  I might be missing your point, though.  I agree the final S/N becomes limited by the film.
> 
> Cheers,
> Jason
> 
> 
-- 
________________________________________________________________
Wei-Hao Wang  :)

Institute for Astronomy at University of Hawaii

Address:                       
2680 Woodlawn Drive         Personal Website:
Honolulu, HI 96822             http://www.ifa.hawaii.edu/~wang
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