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What can be done with just ~25 mins of data

Posted: Sat Feb 22, 2020 1:31 pm
by NeilG
First light for my 2nd new ASI533 - the original had a fault and was replaced by FLO.
I just needed to do some tests - some lights, flats, darks and dark flats to prove that the fault seen in the first camera was absent.
So, here are 3 images all taken on 20th each using 12 sec exposures, gain 110. M82 and M95 total exposure ~25mins, M97 total exposure ~11mins.
Processed in Astropixelprocessor using lights, darks, flats and flat darks, and APPs default stretch.

I'm quite pleased to see the results - very promising for longer exposures. Now to go and play with the in Pixinsight (not tried out the postprocessing features in APP yet.




Re: What can be done with just ~25 mins of data

Posted: Sat Feb 22, 2020 5:31 pm
by mAnKiNd
Looks great, have fun!

Re: What can be done with just ~25 mins of data

Posted: Sat Feb 22, 2020 9:55 pm
by oopfan
Hi Neil,

Your scope, what's the aperture, focal length, and secondary mirror obstruction (if applicable)? I'll model it in software to calculate the signal-to-noise ratio of each image.

In your signature you list a number of different scopes. Which one was used here? Were you using a focal reducer?


Re: What can be done with just ~25 mins of data

Posted: Sun Feb 23, 2020 8:33 am
by NeilG
Its the 127mm Apo @f7.5 - no obstruction, no focal reducer. (oops - forgot to add these to the first message)

sounds like you have a useful tool fort SNR?

Re: What can be done with just ~25 mins of data

Posted: Sun Feb 23, 2020 3:12 pm
by oopfan
Hi Neil,

Here are the results for M82 given 12s exposures and 128 subs. I forgot to ask about light pollution, so here is a range:

Bortle 4: SNR 8.3
Bortle 5: SNR 6.3
Bortle 6: SNR 5.0
Bortle 7: SNR 4.1

Here are the definitions I am using:

Name: Ascension 127mm f/7.5
Aperture (mm): 127
Focal length (mm): 952.5
Central obstruction (mm): 0
Total reflectance/transmittance: 0.99

Name: ZWO ASI533MC Pro (gain 110)
Pixel size (um): 3.76
Read noise (e-): 1.5
Dark current (e-/s/pixel): 0.0003
Quantum efficiency (%): 60

Name: M82 Cigar Galaxy
Surface brightness (mag/sq arcsec): 21.24

My comments:
This calculator was designed for LRGB imaging with a monochrome camera. The SNR values are true for the L channel which is where the bulk of detail comes. A survey of AstroBin images taken with a monochrome camera show that SNR 25 puts you in competition for Image of the Day (IOTD). I ought to run a survey of OSC images to see differences if any.

To achieve SNR 25 in Bortle 5 skies you need to increase total integration time to 6.7 hours. If you increase exposure to 20s then you can achieve SNR 25 in 6.0 hours. Increasing exposure more will further reduce total integration time. Your camera has a Full Well Depth (FWD) of 50,000 electrons so you can go with much longer exposures before star saturation.


PS: Here is M81 that I am working on. I've got 9.1 hours invested in it so far. Tonight I'm going to make another run of RGB that should bring out the blue in the outer arms.

This is what SNR 25 looks like. It is bright. Taken with William Optics 71mm f/5.9 (not APO), camera Atik 314E (5.3e- Read Noise)