From: bugbear on
David Dyer-Bennet wrote:
> I'm interested in
> a high-sensitivity B&W camera for low-light situations.

Have you tried looking at the sort of kit
the astronomers use?

They like "high-sensitivity B&W camera for low-light situations"
to a high degree :-)

BugBear
From: Martin Brown on
On Apr 16, 1:33 pm, bugbear <bugbear(a)trim_papermule.co.uk_trim> wrote:
> David Dyer-Bennet wrote:
> > I'm interested in
> > a high-sensitivity B&W camera for low-light situations.
>
> Have you tried looking at the sort of kit
> the astronomers use?
>
> They like "high-sensitivity B&W camera for low-light situations"
> to a high degree :-)

Although there are comparatively few choices for high MP count. And
they usually need to be tethered to a PSU and a computer. One such is
the Kodak chip based 4Mpixel camera from Starlight XPress:

http://www.starlight-xpress.co.uk/SXV-H16.htm

You wouild want on with the two stage Peltier cooler disabled to get
snesible battery life!

Regards,
Martin Brown

From: Daniel Silevitch on
On Mon, 16 Apr 2007 13:33:18 +0100, bugbear <bugbear(a)trim_papermule.co.uk_trim> wrote:
> David Dyer-Bennet wrote:
>> I'm interested in
>> a high-sensitivity B&W camera for low-light situations.
>
> Have you tried looking at the sort of kit
> the astronomers use?
>
> They like "high-sensitivity B&W camera for low-light situations"
> to a high degree :-)

That, or specialized microscopy cameras aimed at things like
fluorescence microscopy.

In either case, you're not going to get something that's designed to
work well in a stand-alone camera; these sorts of systems tend to prefer
to be tethered to a computer and run off mains power.

See, for example, http://www.piacton.com/ and look at some of the
various cameras under the products/Imaging cameras menu.

-dms
From: David Dyer-Bennet on
Martin Brown wrote:
> On Apr 13, 6:11 pm, David Dyer-Bennet <d...(a)dd-b.net> wrote:
>> Is any company offering removal of the Bayer filter from a Nikon-mount
>> DSLR? Particularly the D40? (I suspect it may not be feasible due to
>> the stacking order and how the microlenses, AA, IR cut, and Bayer are
>> combined, and other issues, and I haven't been able to Google up much,
>> but I thought asking might still turn something up.) I'm interested in
>> a high-sensitivity B&W camera for low-light situations.
>
> Would you not be better off with a faster IS lens?

Maybe, but I'm *already* using 24/2, 58/1.2, 85/1.8, and 135/2 lenses.
The 85 could be a stop faster or some such, and I could add a 28/1.4 or
30/1.4 for various amounts of money (and the 30/1.4 is on the wishlist
currently). I'm reasonably close to the limits in that direction already.

IS wouldn't help much; I'm currently limited largely by *subject*
motion. IS would simplify my shooting some, letting me use my current
shutter speeds in a wider range of positions (not so much need for
leaning against things!). But all the IS lenses I'm familiar with are a
stop or two *slower* than what I'm currently using.

> It might be possible to bleach the filters by exposing the chip to
> strong UV light with some risk of sensor damage increasing the noise.
> Or for certain camera combinations there are pin compatible monochrome
> only sensors. Consumer grade astronomical cameras tend to use them for
> semi serious science work (as opposed to single shot colour). However,
> even though they are excellent in low light they lag behind state of
> the art MP rankings by using larger area pixels.

I'd be happy with 6 megapixels, even 4 would be useful.
Hadn't thought of the bleaching idea, but as you say it's high-risk.

> I doubt you will find a consumer SLR that permits swapping the sensort
> chip, but I could be wrong.

I'm not aware of one and nobody has pointed one out yet, no.
From: Roger N. Clark (change username to rnclark) on
ASAAR wrote:
> On Mon, 16 Apr 2007 10:48:09 +0900, David J. Littleboy wrote:
>
>>> Removal of the Bayer filter would give a lot more light throughput
>>> than 1.5 stops. You have not only the transmission of the
>>> filters but their bandwidths too as factors. If you removed the IR filter
>>> too, I think I computed once that you would gain about 50x in speed!
>> Hmm. At first glance, that 50x seems way over the top, but if the filters
>> actually attenuate in the pass band as well, a factor of 4x (assuming that
>> the pass band is 1/4 of the band from IR to near UV) plus another 2 for the
>> in-band attenuation, and that's a factor of 8x. So three stops is possible.
>> It sounds like you are thinking of shooting under dim incandescent lights
>> where there's a lot of IR and not much blue and green.
>
> At first glance I agree with your first glance opinion. :)
> Charles Schuler posted an informative link in this thread a couple
> of days ago that may clarify the amount of attenuation that takes
> place if the Bayer Filter Transmission vs. Quantum Efficiency chart
> (Figure 4) is a fair representation. It shows fairly broad filters
> with a good deal of overlap, and quantum efficiencies at different
> frequencies ranging from about 8% to 38%, maybe averaging a little
> bit more than 20%.

It is best to use real data when making such estimates,
rather than cartoon diagrams (although the fsu.edu has great
explanations--just not enough info is given on the diagram).
This Kodak data sheet gives more quantitative info:
http://www.kodak.com/ezpres/business/ccd/global/plugins/acrobat/en/datasheet/interline/KAI-11002LongSpec.pdf
See pages 5, 17 (Figure 10), 18 (Figures 12).
The green filter bandpass is about 75% transmission with a bandpass
(called the Full Width at Half Maximum) FWHM = 0.07 microns.
One needs to numerically integrate the area of that bandpass
function times the IR filter spectrum times
the solar spectrum (assuming the sun for the light source),
times the quantum efficiency spectrum and compare that result
with the same integration without the filters.
Figure 1 here shows the solar spectrum through the earth's
atmosphere:
http://speclab.cr.usgs.gov/PAPERS.calibration.tutorial
To first order the bandwidth of the solar spectrum * quantum
efficiency ~ 0.35 microns, so if we assume the IR filter
transmits ~80%, the increase by removing the filters would
be: 0.35 / (0.07 * .75 *.8) ~ 8.3

The factor of 50 I cited previously was from a thread where
different cameras were being discussed and included different
f/ratios between the lenses the systems used too, and compared
to a back-side illuminated 95% QE detector, so that 50x
included more factors than included here.

So for current cameras, 8x or 3 stops is about what we can
hope for by removing the Bayer and IR filters in current
digital cameras, and another stop increase with higher QE
detectors.

Roger
>
>> Interesting idea. Would one necessarily lose the micro-lenses as well and
>> would that mitigate against removal? I don't really know, by the way. Here
>> is an interesting link that might be helpful:
>> http://micro.magnet.fsu.edu/primer/digitalimaging/cmosimagesensors.html
>