Robin Glover on gain, exposure time, e/ADU and read noise curves
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Robin Glover on gain, exposure time, e/ADU and read noise curves
To me this is the most definitive answer that I know of. Enjoy the presentations!
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Re: Robin Glover on gain, exposure time, e/ADU and read noise curves
Then I applied Glover's formula to find the optimum minimal exposure time for a few cases, at 0, 9.99 and 10.01 dB, for
What Glover does not cover is when the stars get blown out. I did some math for that approximating the photon flux for stars as about 30 times that as the light pollution where I'm at,
At any rate, for preventing star blowout it's best to take subs at 0 and 10.01 dB (0 and 100.1 in ZWO's 0.1 dB units). That is also best for minimizing the sub exposure length.
It's a bit nerdy but I got a better understanding of how my camera works and what settings should be best. I attached a little PPT converted to PDF about what I described that I just presented to my local astro club Tuesday night Zoom gathering. Enjoy and don't get a headache.
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Re: Robin Glover on gain, exposure time, e/ADU and read noise curves
Interesting stuff. I really need to give this another try. I looked at it awhile back and found for my sky brightness level, my exposure times would be very short. Couldn't do it!
I like to save all of my lights and dealing with tons of subs and tons of data to store (not to mention processing times in
Of course, I very possibly didn't run the calculations correctly and that is why my exposure times were so short. Have you calculated your optimal exposure time yet? Sorry if I missed it in your post.
Scopes: Explore Scientific ED102 APO, Sharpstar 61 EDPH II APO, Samyang 135 F2 (still on the Nikon).
Mount: Skywatcher HEQ5 Pro with Rowan Belt Mod
Stuff: ASI EAF Focus Motor (x2), ZWO OAG, ZWO 30 mm Guide Scope, ASI 220mm min, ASI 120mm mini, Stellarview 0.8 FR/FF, Sharpstar 0.8 FR/FF, Mele Overloock 3C.
Camera/Filters/Software: ASI 533 mc pro, ASI 120mm mini, ASI 220mm mini , IDAS LPS D-1, Optolong L-Enhance, ZWO UV/IR Cut, N.I.N.A., Green Swamp Server, PHD2, Adobe Photoshop CC, Pixinsight.
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Re: Robin Glover on gain, exposure time, e/ADU and read noise curves
No problem. To me the benefit was to get a better understanding of my camera (and the performance graphs in the ZWO manual), and the whole picture of stacking in function of gain and exposure time. Making the model of the ASI2600 gave me a good understanding of the camera and what the ZWO graphs mean.
Glover solves the minimum exposure choice. For the
A bigger problem is saturation of the stars, which can easily happen with multiple-minute exposures especially if the gain is on the high side. This is nothing new. The math that I did should give some guidelines. Or you can just take a sub of that length and check if the stars are saturated so you can forego the math altogether.
The math that I did for some examples was for
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Re: Robin Glover on gain, exposure time, e/ADU and read noise curves
SkyHiker wrote: ↑Wed Nov 29, 2023 1:25 pmNo problem. To me the benefit was to get a better understanding of my camera (and the performance graphs in the ZWO manual), and the whole picture of stacking in function of gain and exposure time. Making the model of the ASI2600 gave me a good understanding of the camera and what the ZWO graphs mean.
Glover solves the minimum exposure choice. For theBortle levels that most of us have, the minimum exposures are remarkably short. Nobody would pick those short times because you would have to stack a lot more subs than you like. So, in practice, that lower limit is more or less irrelevant. It is nice to know that taking shorter subs is perfectly OK, and that the need for 10-, 20- to 30-minute-long subs for the best results is a myth.
A bigger problem is saturation of the stars, which can easily happen with multiple-minute exposures especially if the gain is on the high side. This is nothing new. The math that I did should give some guidelines. Or you can just take a sub of that length and check if the stars are saturated so you can forego the math altogether.
The math that I did for some examples was forRGB . If you use filters the minimum exposure lengths scale up by a factor discussed by Glover. The saturation times scale up accordingly as well, so the numbers become larger, but staying clear from the lower and upper limits should not be harder.
Got you there Henk.
Absolutely the stars are the biggest issue. I definitely could use improvement there.
Are you going to try using his guidelines for exposure time? What time will you try for your location?
My sky is bright, but I really don't want to go below 30 second exposure times. Actually, I haven't gone below 60 seconds.
Very much looking forward to your results!
Scopes: Explore Scientific ED102 APO, Sharpstar 61 EDPH II APO, Samyang 135 F2 (still on the Nikon).
Mount: Skywatcher HEQ5 Pro with Rowan Belt Mod
Stuff: ASI EAF Focus Motor (x2), ZWO OAG, ZWO 30 mm Guide Scope, ASI 220mm min, ASI 120mm mini, Stellarview 0.8 FR/FF, Sharpstar 0.8 FR/FF, Mele Overloock 3C.
Camera/Filters/Software: ASI 533 mc pro, ASI 120mm mini, ASI 220mm mini , IDAS LPS D-1, Optolong L-Enhance, ZWO UV/IR Cut, N.I.N.A., Green Swamp Server, PHD2, Adobe Photoshop CC, Pixinsight.
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Sky: Bortle 6-7
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Re: Robin Glover on gain, exposure time, e/ADU and read noise curves
If we agree that the star saturation is the biggest problem, then we focus on the gains where we have the most headroom.Juno16 wrote: ↑Wed Nov 29, 2023 1:57 pm Absolutely the stars are the biggest issue. I definitely could use improvement there.
Are you going to try using his guidelines for exposure time? What time will you try for your location?
My sky is bright, but I really don't want to go below 30 second exposure times. Actually, I haven't gone below 60 seconds.
Your 533 sensor is actually very similar to my 2600 in terms of read noise and dynamic range, it is just 14 bits instead of 16.
So, the e-/ADU gain graph is a factor 4 higher with the 533 because of those 2 bits.
The places where we have the most headroom is at 0 dB and right after 10 dB (100 in ZWO units).
Looking at the last slide for
Keep in mind that these numbers are based on a ratio estimate of stars vs.
Anyway, continuing the line of thought, we stay at either 0 dB or 10.01 dB and increase the sub exposure to the point where the stars start clipping. In our case, the 10.01 dB point looks best to start with.
That's what I can come up with so far, I hope it makes sense because I am making it up as I go.
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Re: Robin Glover on gain, exposure time, e/ADU and read noise curves
SkyHiker wrote: ↑Wed Nov 29, 2023 6:36 pmIf we agree that the star saturation is the biggest problem, then we focus on the gains where we have the most headroom.Juno16 wrote: ↑Wed Nov 29, 2023 1:57 pm Absolutely the stars are the biggest issue. I definitely could use improvement there.
Are you going to try using his guidelines for exposure time? What time will you try for your location?
My sky is bright, but I really don't want to go below 30 second exposure times. Actually, I haven't gone below 60 seconds.
Your 533 sensor is actually very similar to my 2600 in terms of read noise and dynamic range, it is just 14 bits instead of 16.
So, the e-/ADU gain graph is a factor 4 higher with the 533 because of those 2 bits.
The places where we have the most headroom is at 0 dB and right after 10 dB (100 in ZWO units).
Looking at the last slide forBortle 5.8, the ADC value relative to the full well at 0 dB is 3467/52428=0.066, whereas at 10.01 dB it is 587/16580=0.035. That means that there is more headroom at 10.01 dB.
Keep in mind that these numbers are based on a ratio estimate of stars vs.LP that is based on one of my images. That ratio depends entirely on how many pixels are covered by a star. My rig has a larger focal length, the collimation is flopping around like crazy, the G11 is struggling with the 65 lbs., so I bet your stars are much smaller and that ratio will be higher in your case. So, adjust it based on what you see in the histogram.
Anyway, continuing the line of thought, we stay at either 0 dB or 10.01 dB and increase the sub exposure to the point where the stars start clipping. In our case, the 10.01 dB point looks best to start with.
That's what I can come up with so far, I hope it makes sense because I am making it up as I go.
Making sense Henk.
I always image at a gain of 104. I guess that I will try reducing exposure time (for broadband) to 30 seconds the next time I'm out. I really don't want to process that many files (or store them), but my file size is much smaller than yours due to my smaller sensor.
Wouldn't hurt to try it out once anyway, just to see.
I just looked in
Thanks for the idea Henk!
Scopes: Explore Scientific ED102 APO, Sharpstar 61 EDPH II APO, Samyang 135 F2 (still on the Nikon).
Mount: Skywatcher HEQ5 Pro with Rowan Belt Mod
Stuff: ASI EAF Focus Motor (x2), ZWO OAG, ZWO 30 mm Guide Scope, ASI 220mm min, ASI 120mm mini, Stellarview 0.8 FR/FF, Sharpstar 0.8 FR/FF, Mele Overloock 3C.
Camera/Filters/Software: ASI 533 mc pro, ASI 120mm mini, ASI 220mm mini , IDAS LPS D-1, Optolong L-Enhance, ZWO UV/IR Cut, N.I.N.A., Green Swamp Server, PHD2, Adobe Photoshop CC, Pixinsight.
Dog and best bud: Jack
Sky: Bortle 6-7
My Astrobin: https://www.astrobin.com/users/Juno16/
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