American Association of Variable Star Observers (AAVSO)
Tue, 09/27/2022 - 04:54


New to posting here so please bear with me.

Has there been any discussion as to the best CMOS camera gains for spectroscopy? I'm going to attach a few graphs to illustrate why I'm asking the question.

The first graph shows the QE of a camera. If you take the "red" cutoff at 800 mn, there is about a factor of 3 difference in the QEs between the min and max. The next picture shows the number of Dynamic Range stops and the read noise as a function of gain. For imaging, the gain of 100 gives the best combo of gain, noise, and dynamic range with about 13.5 stops, or a DR of 11k. 

However, do we need that kind of DR when doing spectroscopy? Do we even need it for Variable Star work?

When doing VS we look at a target and our reference stars are usually within 5 magnitudes of the target unless the target has a huge range, as some do. A factor of 100 is covered by 7 stops so a gain of 400 on this camera would be adequate.

The same argument can be made about spectroscopy work. The dynamic range required between the min/max portions of a spectrum, accounting for the sensor QE, can be handled by a gain higher than what is optimal for imaging.

OK -- I can't attach any images. Maybe because I just joined this group.

Question: when submitting a spectrum, what percentage of the well depth is normal either in terms of electrons or ADU?


American Association of Variable Star Observers (AAVSO)
Why No Images

I did some searching though the AAVSO website and I see that image upload in forum discussions was ended more than a year ago.