Digital BW, The Print

dfaprinting wrote:


> I'm not sure if any 
> manufacturer is doing this for still cameras, but it might be very 
> beneficial for long exposures.

I'm not familiar with any camera maker selling to conventional 
photographers that has a cooled sensor camera, but you might check out 
cameras from Roper Scientific and Apogee. I'm not familiar with their 
current lines, but in the past, a couple models were usable portably. I 
don't recall any of them had faster shutters than 1/10 second, though. 
And the power requirements for thermoelectric cooling are substantial 
(the nitrogen cooled ones require dragging around a tank). On the other 
hand, all of them were monochrome with no IR blockers, and 16 bit.

Cooling will be very beneficial for long exposures, as you say. My old 
10D has 0.25 ADU dark current per second per pixel at ISO 400, with a 
bias offset under 130 ADU. So dark noise on that camera gets significant 
after several minutes of exposure time. I'm more concerned about photon 
noise until out past five minutes or so, at which point I start to apply 
calibration frames to my images to deal with dark and bias noise.

Photon noise is another area in which the larger photosite has a 
commanding advantage. This extrinsic source of noise can't be engineered 
around, but it scales inversely with the photosite's effective area, so 
it can be controlled to some degree.

Sorry, we seem to be hitting all my geek buttons today. I make a 
substantial portion of my living doing scientific imaging, so I'm 
neck-deep in these engineering considerations on a daily basis. OTOH I 
don't know squat about printing B&W.

--
Jeff Medkeff
Eagle River, Alaska