RE: filmscanners: Nikon Scan DOES Vary LED Brightness

["Jawed Ashraf" <Jawed@cupidity.force9.co.uk>]

> -----Original Message-----
> From: owner-filmscanners@halftone.co.uk
> [mailto:owner-filmscanners@halftone.co.uk]On Behalf Of Julian Robinson
> Sent: 27 November 2001 04:49
> To: filmscanners@halftone.co.uk
> Subject: Re: filmscanners: Nikon Scan DOES Vary LED Brightness

> If I was designing the thing, I would use a combination of both.  Normal
> gain would use the LED's at their maximum long-term brightness level - to
> give shortest possible scan time.
>
> - Any *reduction* in "analog gain" would be by decreasing LED brightness
> from that point or decreasing amplifier gain, so the scan time would
> not  change.
> - Any *increase* in "analog gain" would be by increasing
> integration time,

That's a potentially nice solution.  As I said earlier, the "blanking" time
that occurs during each "thrum" step (there are approximately 300) lasts
longer during an AG 4 scan, than during an AG 0 or AG -4 scan.

> thus increasing scan time but not increasing LED brightness or
> analog gain
> beyond the normal maximum.  This might fit with Jawed's observations
> although I take Ed's point that I don't know how you can tell whether an
> apparent brightness change is due to actual brightness change or
> change in
> the duty cycle of the LED (to accommodate changed integration times).

I agree that you can't tell the difference.  I wish that had occurred to me
earlier.

Ed asserted the scan speed is proportional to the analog gain setting.  Well
it isn't proportional.  That's what's puzzling me.

Jawed