Signal to Noise: Part 3 - Measuring your Camera
Posted 09 July 2009 - 10:43 AM
Posted 10 July 2009 - 04:56 PM
Posted 12 July 2009 - 01:16 AM
Some of the software out there will load it as the raw data and others won't. FWIW, one can always use "dcraw" to get this pure sensor data.
Posted 22 July 2009 - 01:45 PM
I'd like to say thanks for the series. I followed the whole guide, and even joined up AstroPhoto Insight so I could read your articles analyzing other cameras.
Some of the results I got are that the system gain of my Canon Xsi (450D) is 0.30 e-/ADU at ISO 800, with a full-well capacity of roughly 4850 electrons with the 14-bit ADC. The read noise was 4.6e- at ISO 800.
However, I couldn't measure the dark current because of the problem you mentioned in other articles: the scaling that Canon applies to the dark frames. The mean of my subframes decreased with increased exposure time while the standard deviation increased, just like you observed. This is really a shame because it means dark subtraction won't work optimally on Canon DSLRs with automatic scaling. I wish there was an option to turn it off. Although, I have to say I haven't noticed this effect from my suburban area; subtracting dark frames gets rid of hot pixels, which is all I'm really looking for as photon noise from skyglow is a much bigger problem than dark current for me. It looks like I will have to revise my habit of taking the read noise out of my image using dark frames though, as the scaling will throw a wrench in this process as well. I wonder if there's any way around it?
One result I got that was anomalous was that the log-transformed histogram of my read noise frame had shoulders almost like you got for the Canon 5D Mk II. Apparently, there is non-repeatable horizontal pattern noise there, because the FFT of the read noise frame still showed a vertical line instead of just random noise. Some disappointing results there, maybe you just put me in the market for a CCD
Posted 22 July 2009 - 07:09 PM
love the series
thanks for writing it up
Posted 25 July 2009 - 10:19 PM
Posted 14 September 2009 - 11:52 AM
System Gain: 0.049 e-/ADU
Full-Well Capacity: 3162 e-
Read Noise: 4.255 e-
Dark Current: 0.010 e-
Dark Stability: About 25 minutes
Bias: Stack of 100 frames FFT, showed 3 faint vertical lines/frequencies.
I'm looking forward to your next installment and some advice on how to take this analysis and do something with it.
Posted 13 October 2009 - 03:26 PM
gain is 0.568 e-/ADU
read error is 6.3 e-
full well capacity is 9143 electrons
dynamic range is 1449 or 32db
dark stability: unknown, std dev of 1-minute darks climbed from 13.9 to 17.4 and had not levelled off after 30 dark frames.
Posted 13 March 2010 - 07:47 PM
I know this is an old thread, but since I got responses from the Sampling thread, I'll try my luck here with another question.
Let's say I'm enjoying imaging with my Canon 40D during the nice cold winter (I assume that the cold weather means better SNR). Now, spring and summer are approaching, which means warmer weather. What will this mean for me?
I would like to prepare for the warmer weather by examining my winter images and calculating what I need to change for warmer temps. Let's say that I like the results I got from 40x300s @ ISO800 @ 35F, meaning whatever that SNR was, it's acceptable and a good target to shot for.
Now, can I somehow measure dark frames taken indoors (72F) and figure out what ISO, exposure length, and # exposures I would need when it gets to be 72F outside to get the same SNR I had during the winter?
Posted 17 March 2010 - 11:48 PM