Gain, Read Noise and Thermal Current of a Canon 450D?

[MarkS]

Robert,

Following our discoussion at Kelling Heath, the procedure for calculating Gain, Read Noise and Thermal Current is here:
http://forum.orpington-astronomy.org.uk/index.php?topic=3473.0

If you have a spare rainy afternoon I would be very interested in knowing the results for the 450D.

Or send me the RAWs and I'll do the calculations.

Mark

[RobertM]

Thanks Mark, I'll do that soon.

[MarkS]

Christian Buil has done an analysis on some Canon cameras to determine their Quantum Efficiency - he compared their photon collecting ability to a known reference Camera.  It's the first time I've come across such a useful analysis. 

He's come up with a figure of a paltry 35% max QE, the maximum occuring in the Green band.  By comparison, the Kodak chip in the QSI reference camera had a max 85% QE and that was in the Ha band.

http://www.astrosurf.com/~buil/50d/test.htm

The good news is that there must be plenty of scope for huge improvements in future DSLRs!

I was thinking about this the other day - wouldn't it be useful if DSLRs had a Bayer matrix like:

GRGR
BLBL

instead of the usual

GRGR
BGBG

That would improve DSLR low light perfromance by an order of magnitude.  Or am I missing something?

[Ian]

I understood that the reason there are more green sites than the other colours is to reflect to greater green sensitivity of the eye. I would think having L sensors to deal with as well would significantly increase the amount of processing the raw signal from the ccd would need to have applied to make use of that additional information.Which in the most usual use of the CCD can be derived quite reasonably from the RGB sensors.

I think the point being, these cameras and chips are being made for one purpose only and it's a very lucky accident that they are sufficiently flexible that we can take them right to the limit of their capabilities. A higher QE would be nice though

What we would need is to find a big enough market for astronomical sensors and persuade Kodak or someone to make a limited run with a modified matrix

[mickw]

How about the Foveon set up like Sigma ?
http://www.sigmaphoto.com/cameras/sd14_feature_01.asp

[Ian]

off the top of my head, I believe that sensor works by vertically stacking the photosites increasing the resolution (removing the need to interpolate from the bayer matrix). It would suffer from poor low light performance due to losses as the photons travel down the stack.

Of course, I didn't look this up and it could be total B*(*^&&^%*&%ks.

[RobertM]

Ian,  I think you're right.  Except it had the problem you mentioned - it's just as well they didn't put 100% satisfaction or your money back on the tin !

Mark, It's been a busy week but should be able to get around to doing the measurements over the next few days.

PS. where is everyone, the forum is deathly quiet - has everyone got Swine Flu !

[Ian]