American Association of Variable Star Observers (AAVSO)
Sun, 07/18/2021 - 11:26


I am a 20+ year visual observer but I am transitioning to EAA and I also want to begin contributing science to this community. I have been researching CMOS cameras for my 14 inch LX600 and I have (hopefully) narrowed my choices down to a couple of options that seem to cover most of my requirements: ZWO ASI533MC Pro or the ZWO ASI2600MC Pro. I’d prefer a color camera because I will also use it for general EAA observing, but my priority is making sure that I can do photometric measurements of variable stars. I have a narrow window for buying a camera, basically I need to decide in the next day or two. 

So, two questions that I need advice on:

1.  Is one of these cameras better for photometry?  I know that is not a simple question because there are many considerations, but if had the opportunity to choose one for variable star observing and measuring, which would it be? Do you have experience with either?

2. Is there a clear advantage to a mono camera or would a color camera be acceptable?  Again, I know there are many considerations but I need to decide from a overall, this-is-my-only-camera, perspective. 

Thank you very much in advance for any advice!


Bundesdeutsche Arbeitsgemeinschaft fur Veranderliche Sterne e.V.(Germany) (BAV)

Hi Jim,

I am also thinking of upgrading from DSLR to a CMOS with the new SONY sensor,

one thing you can do is

  • optimizing PIXEL vs. FOCAL LENGTH


to avoid over or undersampling.  I use focal lengths from 500 mm to 1200 mm max! Maybe you can use a focal reducer for your F=2845 mm ?

  • A monochrome camera is much more sensitive than RGB, so think maybe of using a filter wheel (But if you only occasionally go for variable stars or exoplanets, a color camera with the Bayer Matrix RGB will do ok.)
  • A shutter makes life easier! You can programm e.g. 10 lights, and one dark frame (with the shutter) during the whole night! Otherwise you have to do darks manually...
  • CCD...hmm is olden but golden...(and therefore much more expensive..)  I have waited for CMOS sensors to be produced with16 Bit: Sony IMX571or Sony IMX455
  • You'll need a "non ABG" ( anti blooming gate) This is only good for pretty pictures, that stars are not getting bloomed... but with photometry linearity is much more important ( If the detector is still counting photons, but the ABG is cutting them of.... one would get false measurements..)


But there are many CMOS cameras with the new Sony sensor. Sony IMX571or Sony IMX455  QHY 600, Touptek DeepSky Pro 2600m monochrome,   ASI 2600 MM Pro,69615#tab_bar_1_select

or Moravian

maybe one of these:



Have you seen the very good AAVSO webinar CMOS vs CCD on Youtube?





EDIT: The,64309#tab_bar_1_select

has only 14 Bit so i'll definitve go for 16 Bit! And high QE.. and high Full Well Capacity ...


American Association of Variable Star Observers (AAVSO)
CMOS on a bit more of a budget?


I respect the capabilities and specs of the Sony571, 455 and 2600 but is it possible that the mono 294MM or 183MM, at lower costs, might also be reasonable choices given budget limitations? I'm currently using the 294MC and submitting TG data but I'd like to move to mono with filters and transition to submitting transformed V and B data. I'd appreciate any thoughts and suggestions in that vein.



American Association of Variable Star Observers (AAVSO)
Transform TB, TG, TR


Why not generate transform coeffs for your color array filters and transform your mags to BVR? It works reasonably well, especially for the TG channel. Take images of standard Landolt fields to see how your transformed magnitudes compare to the Landolt standard magnitudes. This requires no extra capital cost to you.

I'm not implying that the monochrome filters would not be a better choice (more accurate) but it can be done.

BTW, do you know that the AAVSONet BSM cameras are the ZWO CMOS 183MM model? They work fine for photometry.