Altair 26C & 26M Gain

Discussion of features and issues relating to Altair Astro Cameras
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ALAMEE
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Altair 26C & 26M Gain

#1

Post by ALAMEE »

Hi,

I have Sharpcap pro with AA26C as well as AA26M, but I keep switching between Sharpcap and NINA. I would highly appreciate some guidance in the following:

- I did sensor analysis for AA26C with sharpcap 3.x and gave me optimum gain @ 316
- I did sensor analysis for AA26M with sharpcap 4.x and gave me optimum gain @ 200

1- Is their a difference in sensor analysis between sharpcap versions, or the difference based on the fact that we have different sensors in these two cameras?

2- As I switch between Sharpcap and NINA, I have been using same gain from sharpcap with NINA but I FEEL that results are different, is that in my head only or I should use different gain in NINA than the one identified by Sharpcap?

Thanks in advance.
Attachments
AA26MTEC.png
AA26MTEC.png (65.48 KiB) Viewed 8440 times
AA26CTEC.png
AA26CTEC.png (65.43 KiB) Viewed 8440 times
Best Regards,
Albert L.
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Re: Altair 26C & 26M Gain

#2

Post by admin »

Hi,

I think that the AA26M/C models have the 'Ultra low noise' option, and the difference in read noise measurements between your two graphs looks like you had one camera in ULN mode and the other camera in normal 16 bit mode. That seems the most likely difference, anyway. The difference in results may impact the suggestions for optimum gain, etc.

Now, why do things seem different in NINA?

This sensor (like quite a lot these days) has two types of gain.

1) The normal gain control
2) A switch between 'Low Conversion Gain' (LCG) and 'High Conversion Gain' (HCG) mode.

Switching from LCG to HCG adds some extra gain on top of the normal gain (in the case of this camera, it effectively doubles the image brightness), but also tends to reduce the read noise quite a lot.

SharpCap automatically combines the two types of gain into a single slider. NINA does not (as far as I know).

So...

NINA 100 gain LCG is the same as SharpCap 100 gain.
NINA 199 gain LCG is the same as SharpCap 199 gain.
NINA 100 gain HCG is the same as SharpCap 200 gain.
NINA 200 gain HCG is the same as SharpCap 400 gain.
NINA 300 gain HCG is the same as SharpCap 600 gain.

SharpCap does it this way because it seems that when you have two ways of reaching a particular gain brightness - ie LCG, 500 gain or HCG 250 gain (both give a brightness of 5x minimum gain) - the HCG option always gives a lower read noise and hence a higher quality image (e/ADU and FWD will be the same).

Hope this helps,

Robin
ALAMEE
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Joined: Sun Sep 26, 2021 3:34 pm

Re: Altair 26C & 26M Gain

#3

Post by ALAMEE »

Thanks a million Robin, This means I have been missing out on Dynamic range (13.3 vs 12.4) as I have been using 200 gain on NINA with HCG selected ON.
I have noticed that histogram was shift about 10 to 15% on NINA vs SharpCap with same gain of 200 and exposure on AA26M. Maybe cause the full well is half so sensor saturate easily, I guess!?
I better start learning plate solving in SharpCap so I can migrate back to it completely.
Thanks again.
Best Regards,
Albert L.
maclean
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Re: Altair 26C & 26M Gain

#4

Post by maclean »

Hi Robin,

I also wanted to ask a similar, quick question about the gain settings for my 26(C). Back on [2 Jan 2021], I ran the sensor analysis with whatever version of SharpCap I was using at the time (not sure exactly which one), and the switch from LCG to HCG appeared to happen at a gain of 300.

I just repeated the sensor analysis today [28 Dec 2022] with v4.0.9455, and it appears the HCG switch happens at a gain of 200.

Just so I understand, is this something you have changed in SharpCap, or something that changed in Altair's underlying driver?
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Re: Altair 26C & 26M Gain

#5

Post by admin »

Hi,

can you just check for me what name appears for your camera in the title bar (and Cameras menu) in SharpCap.

Unfortunately SharpCap has to depend on camera names to know the point to switch to HCG mode, and if a new SDK or driver has changed the name of the camera, it could mean it no longer matches the list that are set up for the 571 sensor and falls back to the default of 200 gain changeover point.

cheers,

Robin
maclean
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Re: Altair 26C & 26M Gain

#6

Post by maclean »

Certainly. Using v4.0.9455, my camera appears with the name "AA26CTEC"
Also attached is the sensor analysis that it generated a couple days ago if it is helpful to see it.
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SensorAnalysis-26C.png
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Re: Altair 26C & 26M Gain

#7

Post by admin »

Hi,

yes, it looks like the display name of the camera has changed since I had a sample to work with, which is stopping the 300 gain switchover point from being applied correctly. You can see in your data that the HCG mode is coming on at gain 200, but the actual brightness increase at that point is a factor of 3 (look in the relative gain column).

I will fix that for the next update.

cheers,

Robin
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Re: Altair 26C & 26M Gain

#8

Post by maclean »

Thanks! I do not have the mono version unfortunately, but that might have changed too. Is the value of 300 a value you selected? I am just curious, but what is the rationale for picking that particular value?
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Re: Altair 26C & 26M Gain

#9

Post by admin »

Hi,

the fix I have will affect both the colour and mono cameras, so look out for the next version (and re-run your analysis once it is available).

The value is based on the amount of additional gain that the LCG=>HCG switch gives. This is fixed for a particular model of sensor, so for the IMX571 sensor in the 26C and 26M, the additional gain is a factor of 3 (or very close to that). Gain 300 on an Altair camera is 3 times brighter than minimum, so we set the LCG=>HCG switch over at that point. Up to gain 300 your gain is controlled by the standard analog gain adjustment of the camera. At gain 300, the analog gain is set back to minimum and HCG is switched in (getting you 3x gain but by a different route). Above that point the standard analog gain goes up again to increase the total gain (in addition to the 3x gain from HCG).

For some sensors we switch at a higher point than the gain given by the LCG/HCG switch due to other considerations (ie the IMX 294 sensors fall into this category). It's all worked out so that in theory the imager just sets the gain and gets the best possible combination of settings for that gain without having to worry about it.

cheers,

Robin
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