is the tutorial about gain values valid for most apertures?

benni

Hi, you have here made a tutorial which explains what gain value one should choose to get the highest snr from the asi 1600 and other cameras:

https://astronomy-imaging-camera.com/tutorials/cooled-asi-camera-setting-in-ascom-driver.html

For this tutorial, you have used an f4 telescope. You concluded that short exposures and lowest read-noise would yield the highest signal to noise ratio.

I wonder whether this is also valid for slower apertures, like the f10 of typical schmidt cassegrain telescopes?

The reason for my question is that with slower apertures, you need to make longer exposures in order to collect enough photons.

It could be that for an f10 scope, you have to make exposures long enough that the noise of the low red noise setting then has a negative impact on the snr.

Is that so?

Or is there still a signal to noise ratio advantage at lowest read noise setting with short exposures if one uses a slow f10 telescope?

Best regards

Benni

katherine.tsai

Hi,

I think it depends on what objescts you want to capture, if you want to do planetary image you must use shot exposure, for DSO imaging, long exposure is required, and for your f10 telescope, you will need longer exp time.

benni

Hi, the thing is that the asi 1600 has such a low noise level that one can make short exposures even with nebulas.

My question was the following

If I remember correctly, you have shown in your link with an f4 scope, and a stack of the crab nebula where each image has 10 seconds exposure time, that you get a better snr with lowest read noise setting.

My question is whether this holds at all appertures.

Say we have the same object, the crab nebula, like in your example, but now at f10 instead of f4.

I would either need a longer exposure or a higher number of images to get the same snr and signal.

Assume I chose a longer exposure. f10 is approx 3 aperture steps away from the f4 of your system. So i guess, in order to get the same signal, I would need a stack of the same number of images, and each image with an exposure time of 10*2*2*2=80 sec .

Is then, with this longer time for each image, still the lowest read noise setting giving a better snr than unity gain?

Or does the noise get overhand, reducing the snr?

Now assume, i want to get the same snr and the same signal with more images instead of a longer exposure. So how many images would I need, if I have again the crab nebula, 10 sec exposures and an f10 scope instead of your f4?