Pitch Black Skies

This is quite low though compared to mine. My camera's default offset is 70, yet my bias ADU is nowhere near that figure, it's 2796 median ADU. Even 2796/16 = 174.75. Still nowhere near 70. Why is Jon using 50 in his equation but I'm not using 70? I'm missing something very basic here 🧐

In the CN thread you shared, Jon Rista uses the ASI1600 default offset of 50 in his equation. He doesn't use the median ADU of his bias sub. I am missing something here?

True 😄 and I'm gonna put my hands up on this one. There's a 99.99% chance that it's me who isn't. I've repeated the steps from the beginning with the same files. This time I'm getting ~105, ~106. When I select the centre of the green flat, I get a Mean of 13266.104. I remove the selection and then divide that flat Green by 13266.104. Then I'm dividing the light Green by that flat Green, and then dividing the resulting image by 4.

I've followed all of the steps and selected a few different patches in the final image and measured them. They are all ~131 or ~132 Median. Does that sound right to you? I was expecting to get ~77 or ~78 like yours.

Well if you're doing it like that, I am too 😁

Any reason for the specific numbers? I've noticed they are both 2^6 and 2^8 respectively.

In DSS, I have Intersection Mode, and Kappa-Sigma clipping (Kappa: 2.00 Number of iterations: 5) selected. Alignment is set to Automatic.

That's interesting, I'll be able to check the DSS settings this evening. The parameters were all the same. I remember I had to use 10s for the flats to get the ADU around the 20k mark. Not sure if that was a bit too long. How many would you usually shoot for, 100?

They are a stack of 20 single files each. Do you think I should increase to get a more averaged out master? I'm going by the reccomendation of 20 in the book 'Every Photon Counts'.

Something's not right here. The master flat doesn't look right. Also, when I subtract the master flat dark from it I end up with a completely white uniform image with no vignetting 🤔

@vlaiv Not sure what I am doing wrong on ImageJ. File - Open raw sub Image - Type, RGB Image - Colour, Split Channels Select square patch similar to yours from yesterday Analyze - Measure I'm getting a Mean of 1,493 ?

This is straight from the camera to my ASIair Pro. I think it is the same file that I attached yesterday. Light_M101_300.0s_Bin1_533MC_gain100_20220402-231650_-10.0C_0002.fit

300s raw sub.FTS MasterDark_Gain100_300s.tif MasterDarkFlat_Gain100_10s.tif MasterOffset_Gain100.tif MasterFlat_Gain100.tif I hope these are okay. I never calibrate with the Master Offset as I've (read that) Flat Dark/Master Dark contains that signal.

Yes, really appreciate that. I will do it this evening. I don't recall seeing an option to save as 32bit floating point. I think it is just 32bit integer/32bit rational, fit/tif.

300s sub calibrated.FTS

Does it mean just to use 1 flat? For the M101 sub, I have the master dark, master flat and master flat dark. Shall I calibrate it, upload it and see what figures you can pull from it? What program can I use to measure the background like you did? The software I use are in my signature. I'm trying to load the file into NINA but having no luck.

For this method my LP noise = 57.58 Mean ADU from your analysis = 3316 829*4=3316 √3316=57.58 LP noise In the other method you got LP noise = 130 829-699=130 LP noise What am I doing wrong here? Edit: I think I could be mixing LP noise up with LP signal in the second calculation.

Is that not for the light pollution swamp?

Also a much simpler way to calculate.

This is clever, more simple.

Yes, it's a lot clearer now. Take a quick look at my latest attempt please to see if I understand it correctly. I find your method of the RNx5 a bit more straight forward.

I think I am confusing Jon Rista's reccomendation for swamping read noise squared * 10.

I was writing the gain as 100 rather than 1. The gain is supposed to be expressed as e-/ADU which is 1 for me at Unity Gain. Vlaiv actually explained this to me earlier. I'm still not getting the end part of the formula (2^16/2^bits). Jon just multiplies by 16 in his equations. That leads me to another question, should I be multiplying by 14 as my camera is 14bit, or even 13.5 as that's what unity gain brings it down to? Here's my latest attempt:

Awesome, thanks so much. Does this mean that if I went with a recommendation of 10x swamp factor, I would be underexposing by almost 58%? 1.5 * 10 = 15, 15^2 = 225 130/225 = ~.58

I think I've read that the default offset for this camera is 70 as per ascom driver? I can't wrap my head around Jon Rista's formula. What am I doing wrong here? Btw does DN mean data numbers?