Unity Gain question

billm

I have a ASI183MM-Pro using latest drivers.

I have noticed that in the Camera Manual, Unity Gain is shown as 120 but in the Ascom driver settings dialog, under the Unity Gain pre-set, Gain is shown as 111.

Am I misunderstanding? Which is correct.?

Thanks

Bill

chad

Hi Bill,

Sorry for the problem.

To be honest, neither of these values is strictly accurate.

As we know, Unity gain means one value maps one eletronic. Consider noise and the limitations of test conditions. We can only approximate this value.

For 120, It is inferred from the curve which is fitted by a series of tested points.

For 111, it's a mathematical algorithm value from the tested point.

Usually, please use the 111, because the scale of the curve, when inferred, It's hard to get within 10. And, usually for easy of introduction, we will choose some of the easy-to-remember values on our manual.

Thanks

Chad

billm

Hi Chad

Thanks for the reply.

Are you saying the 120 is the straight line interpolation but that the 111 comes from the actual formula? Does that mean the 270 gain setting for LRN in the Ascom driver is the correct value too?

Thanks

Bill

chad

Hi Bill,

For the gain, Only the unity gain is calculated.

For example, there is another camera.

when set gain=0, we can test the electronic gain is 1.5 e-/ADU, At this gain, we will get the largest full well capacity.

When we set the gain=60, we can test the electronic gain is 0.9 e-/ADU.

When we set the max analog gain=120, we will get the lowest read noise, at this point, the electronic gain is 0.2e-/ADU.

If we continue increase the gain, the camera will use the digital gain, the read noise and the electronic gain will not change, they just get amplified by the digital gain.

So LRN usually means the max analog gain is 120, it must be a correct value.

But for Unity gain. if we draw a curve with the data we tested, you will find the gain is around 50 when electronic gain is 1.0e-/ADU. But if you use the mathematical algorithm to calculate it, you may get 45 means electronic gain=1.0e-/ADU. But in the truth, maybe electronic gain equals 1.0e-/ADU when the gain is 46.5.

Please forget my poor drawing.

Thanks

Chad

billm

Hi Chad

Thanks for the info. What is the max analog gain for the asi183mm pro?

Bill

chad

Hi Bill,

it should be 270.

Thanks

Chad

warnergrict

Yes, thats what I see almost everywhere. The unity gain calculator at that one site, which has the most extensive selection of calculators Ive found, delivers results with R1 and R2 having different values.

qwer

Please tell me how to get to Pre Defined Settings? I have driver version 6.0.3.23 on the ASI1600MM - there are no such settings.

chad

Hi Qwer,

It is ASCOM, if you connect the camera with ASCOM, you can find it.

Thanks

Chad