Sharpcap 3.1 AA183M sensor analysis for Gain/offset/exposure time

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AstroDude
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Sharpcap 3.1 AA183M sensor analysis for Gain/offset/exposure time

#1

Post by AstroDude »

How to find the best GAIN/Offset/Exposures for your new Altair Astro camera.
using SharpCap 3.1 sensor analysis.
hope this helps someone...

https://www.youtube.com/watch?v=QgX9XDZ ... e=youtu.be

Mitch / Astrodude
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Re: Sharpcap 3.1 AA183M sensor analysis for Gain/offset/exposure time

#2

Post by admin »

Hi Mitch,

that looks great! What do you think about moving this thread to the tutorials forum? I think it would fit nicely there.

cheers,

Robin
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oopfan
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Re: Sharpcap 3.1 AA183M sensor analysis for Gain/offset/exposure time

#3

Post by oopfan »

Hi Mitch,

Great YouTube video although I disagree that the Optimal Black Level is zero. I know that you are following the Brain's recommendation so this critique is aimed at SharpCap not you:

The purpose of Black Level is to prevent data loss (i.e. clipping) on the left-hand side of the histogram. This is almost never a problem with Light frames because the background sky brightness is never truly black unless you are blessed with extraordinarily dark skies. The problem is with your Calibration frames. When you acquire Dark frames you completely cover your objective so no light reaches the sensor -- you are only measuring thermal noise. Thermal noise in a CMOS camera is low, and it is my experience that you are losing data by setting Black Level to zero.

I have successfully used the Brain to take some great astrophotos but I have learned to never allow my Black Level to be zero. I have a 12-bit A/D like you, Mitch. I always dial in a Black Level of at least 100 (ADU Counts).

Here is a great post by Craig Stark entitled "Gain, Offset, and Bit Depth": http://www.stark-labs.com/help/blog/fil ... Offset.php

Brian
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Re: Sharpcap 3.1 AA183M sensor analysis for Gain/offset/exposure time

#4

Post by robrj »

I liked the video as well. Robin, is it preferred to leave the camera in the scope? I thought I read it was better to do the sensor analysis with the camera only.
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Re: Sharpcap 3.1 AA183M sensor analysis for Gain/offset/exposure time

#5

Post by admin »

Hi,

either way works for the sensor analysis as long as you can get the right illumination level and the light source is steady.

cheers,

Robin
barnold84
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Re: Sharpcap 3.1 AA183M sensor analysis for Gain/offset/exposure time

#6

Post by barnold84 »

Hi,

This is a great video. I just bought the AA183M (fan cooled) in February. Since I had issues in finding the right settings for the camera, I read a lot and I also watched Robin Glover's videos which are very helpful to quickly pick up the theoretical concepts and ideas. Since I am using a RapsberryPi to capture my light frames, I cannot use he smart histogram while capturing but I used the sensor analysis function to gather my sensor specifics and also implemented a small Excel sheet to compute the ideal exposure time.

My actual question is related to differences among cameras of the same mode:
Here, I am sharing the table that I got out of the sensor analysis from SharpCap. Unfortunately I didn't make a screenshot and had read the data again into the software. I hope I did the DR calculation correctly at least.
Sensor analysis barnold84s AA183M
Sensor analysis barnold84s AA183M
Bildschirmfoto 2021-04-08 um 08.54.17.png (334.81 KiB) Viewed 1281 times
Here's a screenshot of an analysis that my vendor posts on his website:
Sensor analysis shown on vendor website
Sensor analysis shown on vendor website
Bildschirmfoto 2021-04-08 um 08.56.09.png (948.86 KiB) Viewed 1281 times
I was very surprised as these numbers differ quite a lot. If I'd go to the info according to the vendor, with a gain of 350, I'd still have a DR of 11,31 while for my camera I am close to 10!!

Is this a common observation?

Just to note: the light source I've used was an iPad... and as I am writing this it dawns to me that I didn't place the luminance filter on the camera and shot only with the protective glass that the camera has (transmission 350 to 1050nm)... I guess that might be an issue as well?

Edit: I did another analysis making sure that the exposure times are a bit longer since the iPad shows some flicker that the camera recognizes on low exposure times. Also placed the L filter on it, although I guess it wouldn't do anything? Numbers seem to match the vendor's result better.
Sensor analysis barnold84 2nd
Sensor analysis barnold84 2nd
Sensoranalyse.png (169 KiB) Viewed 1276 times
CS!
Björn
Last edited by barnold84 on Thu Apr 08, 2021 9:22 am, edited 1 time in total.
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Re: Sharpcap 3.1 AA183M sensor analysis for Gain/offset/exposure time

#7

Post by admin »

Hi,

I'm unsure about the figures on the Altair web site - I have tested the 183M that I have here and get slightly better read noise values than you (3.33 at minimum gain), but cannot replicate the read noise values on the Altair site for higher gain values. I get very slightly lower noise levels (0.01-0.02 less) if I turn off the fan.
Capture.JPG
Capture.JPG (98.41 KiB) Viewed 1263 times
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Re: Sharpcap 3.1 AA183M sensor analysis for Gain/offset/exposure time

#8

Post by admin »

One more thing...

Note that the graph on the Altair web site has a linear horizontal scale. This changes the shape of the curves, making it seem to fall away more steeply, but also indicates that it was generated with quite an old version of SharpCap. I have made improvements and fixes to the sensor anslysis code over the years, so it's just possible that some of the read noise difference could be related to the SharpCap version change .

Robin
barnold84
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Re: Sharpcap 3.1 AA183M sensor analysis for Gain/offset/exposure time

#9

Post by barnold84 »

Hi Robin,

Thank you for your reply! I didn't notice the difference of the axis's scaling until you mentioned it. Although I didn't go for the graphs to compare but for the plain numbers. So after all, I assume my first measurement had issues and probably was connected to the light source (iPad settings) and certainly also measurements are subject to some uncertainty?

I have one more question and that's probably an easy one but somethings blocking me from seeing it. At first I thought the dynamic range provided in the table was based on the basis of 2 (i.e., powers of two) but it's not. How do you compute the dynamic range?

May I ask, do you use the 183M yourself for deep sky imaging? In case so, how is your experience?

Cheers,
Björn
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Re: Sharpcap 3.1 AA183M sensor analysis for Gain/offset/exposure time

#10

Post by admin »

Hi Bjorn,

I calculate dynamic range as FWD / Read noise. Essentially it's the brightest thing you can measure without being quite saturated divided by the dimmest thing that can be measured above the noise floor.

I must admit that my imaging is rarely serious in terms of getting the most out of the camera - I am usually testing out software features and therefore end up compromising my final images in order to get the tests done that I need to. I've seen good images put together with this camera, but it's no longer cutting edge - I can see from my records that I was looking at this camera over 4 years ago now in prototype form...

cheers,

Robin
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