I am a programmer so I have written a program to display my RAW data. The D5300 RAW data ranges from 600(Black Level) to 16383(Saturation) counts. At ISO200 the Full well capacity of the D5300 is 16968. I used DCRAW to extract the RAW data and debayer the RAW data into a 16b TIFF without applying scaling or whitebalance. The values in the resulting TIFF file can be considered representative of the D5300 RAW data. I chose to focus in on a small area at the centre of my image because I wanted to study the range of values that are typical for these "faint fuzzies".
I picked a single LIGHT frame (DSC_0015.NEF) and wrote a program to only display RAW data that ranges from 560 to 815. Any values brighter than 815 are pure white. I also add a feature where I could position a yellow rectangle that is 30 x 30 pixels in size. I then calculated average, standard deviation and SNR values for these 900 pixels for each colour. No BIAS, DARKs or FLATs were used...this is RAW data right from the camera. You can clearly see the hot pixels. In this image, the yellow rectangle is positioned at a very dark area. The average RAW data values are (R,G,B) 638, 641 and 617. The standard deviation values are (R,G,B) 5.8, 6.3 and 5.7. The SNR values were (R,G,B) 6.4, 6.6 and 3.0.
The average Red pixel value of 638 minus the 600 "black level" means that I was only able to collect 38 counts. At unity gain I believe that 1 count = 1 electron so I think I collected, on average, only 38 electrons in the red pixels for this area. Since this was a 500 second exposure this means, on average, I was collecting 1 electron every 13 seconds. I think my
My take-away from this analysis is that my 8"EdgeHD+D5300 system does not collect photons very fast. A cooled astrocam is not going to change this situation unless it has bigger pixels and/or higher quantum efficiency. If I was able to make these improvements I could take faster photos and, for the same 2-3am curfew I could have more photons counted in my data. To me...more photons counted = better data. For this next image I have moved the yellow rectangle to directly beside a bright star where the nebulosity glows a bright yellow. The average values here are (R,G,B) 670, 674 and 635. Standard deviations are (R,G,B) 11.0, 10.1 and 7.6. SNR values are (R,G,B) 6.4, 7.4 and 4.6. Again, using the red pixels as the example, I notice that the average value has increased from 638 to 670. This change of 32 counts tells me that astrophotography is all about making very faint changes much more visible. This is a change of 32 counts in a data file that ranges from 600 to 16383 counts. The D5300 is a 14 bit camera. In order to achieve this 32 count difference I chose a 500 second exposure that resulted in several thousands of saturated pixels that most likely exceeded their fullwell capacity. I don't think I want to entertain a cooled astrocam that uses a 12 bit
So my opinion is that I need a 14 bit, or better, cooled astrocam with bigger pixels and a higher quantum efficiency.
Well I found one...the only issue is that it's a colour camera. It's the ZWO ASI294MC Pro. The pixel size increases from 3.91uM(D5300) to 4.63uM. The quantum efficiency increases from 60%(D5300
I want to be able to shoot narrowband so a colour camera is not ideal but there are several users (Trevor Jones) who are getting great results with duoband filters. I would purchase a manual filter wheel and just shoot RGB on moonless nights and narrowband on moonlit nights.
The only alternative camera I considered was the ASI1600MM Pro which is a clear winner for shooting narrowband. But it's pixel size is smaller (3.8uM) and it's quantum efficiency is the same (60%). This means that the ASI1600MM would be a slower camera than my D5300. Combine that with its 12 bit
Thank-you for reading this and I look forward to your comments.