New Altair 585M Sensor Analysis Q's & Issues

[admin]

Here's the results I get from analysing HDR mode on my ToupTek 585 colour

Screenshot 2025-01-20 165134.jpg (103.11 KiB) Viewed 3661 times

The shape is very similar to your measurement, but all of the full well, read noise and e/ADU values are about 3x lower. All of these come from the initial measurement of e/ADU at minimum gain that is done at the start of the analysis - if the first plot was a bit random rather than a straight line then that could have been a bad initial e/ADU measurement, or it could be something odd in the SDK.

Obviously something weird happens beyond gain=10000 with the rising read noise, but to be honest, that range is pretty much not used anyway - certainly not for deep sky, so it doesn't matter much what happens out there...

cheers,

Robin

[Olivier-Fantasy]

Thanks a lot, Robin,

So, you advise me to prepare my darks for a gain of 1365 (I often practice EAA and a little astrophotography, under a Bortle 8 sky)?

[admin]

Hi,

the best thing to do is to run the 'smart histogram' function that will measure your sky brightness and advise on the appropriate gain and the minimum exposure required for your conditions. With bad light pollution, you may find that you can stay at lower gains in LCG mode and still get reasonable sub-exposure times - certainly worth considering if gain 1365 turns out to give you too many very short exposures to stack.

cheers,

Robin

[Olivier-Fantasy]

Good idea!! (again ) Thanks a lot!

[TerryMcK]

I too am intrigued as to what gain I should set the AA585M to. I have just completed my sensor analysis and get very similar results.

sensoranalysis AA585M.png (28.39 KiB) Viewed 3630 times

sensoranalysis AA585M graph.png (17.94 KiB) Viewed 3630 times

I had the camera out last night (surprisingly just after PAS2025 where I picked the camera from! - that isn't normal I have had to wait weeks in the past for first light on anything!). Anyway I had it on a RedCat51, saw the 1365 gain you have stated and when I finally removed a spacer ring from the optical train got it to focus. I only got a few frames before it clouded over but was disappointed with the results from 5 minutes subs. Very dim indeed on a typically bright Ha object. Then I noticed the high gain mode hadn't been turned on in Nina using the Altair SDK.
I might try it out again tonight with high gain mode turned on but overall disappointed with the camera. Not as easy to use as ZWO's.

[admin]

Hi,

gain 1365 where the camera switches from LCG to HCG in SharpCap is definitely a good starting point, as the reduction in read noise allows the use of exposures that are a factor of *12* times shorter than you could get away with at gain 1364, and a massive 41 times shorter than using gain 100.

I'm not sure if you are comparing to a ZWO IMX585 camera or another ZWO camera, but there are a couple of things to be aware of when making comparisons:

* The IMX585 has 2.9 micron pixels, meaning that each pixel only collects about 60% of the photons when compared to a camera with 3.75 micron pixels (like the ASI2600) and only about 39% as many compared with something like the ASI294MC with 4.6 micron pixels

* Gain values work differently for Altair cameras than ZWO - this means that you can easily end up with thinking the camera is brighter or dimmer because equivalent gains have not been used. A rough equivalence chart is

ZWO Altair
0 100
100 316
200 1000
300 3160
400 10000
500 31600

cheers,

Robin

[TerryMcK]

Yes I am comparing relative dimness to ZWO ASI183MM, ASI2600MM and the ASI294MM cameras that I also have.
I'll have another play around with the AA585M before writing it off.
Very useful information. Thanks Robin.

Terry