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Luminance imaging to get fainter stars?

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#1 Agreegator


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Posted 23 September 2021 - 01:06 AM

I am really fascinated by capturing really really low mag stars and then finding them on charts and researching their properties, details, etc . That and planetary imaging is all I ever do in my astroimaging. No widefield stuff.  


With my 150mm MAK, I am starting to hit a limit at mag 17.5 .. ish stars . I want to go even lower. Changing the scope is not an option for me (I travel a lot and it has the perfect,  weight, resolution and mirror size for going into luggage). The only improvement I can think of is upgrading the camera ... Currently I have a Cooled Colour CMOS and I was wondering if mono luminance camera can help me get fainter stars?


Below are the specs I'm thinking about. I want a cam specialized at really narrowfield stuff - as I normally select an study just a few stars at a time. Shipping & Customs add to about 200% where I live so I do not want anything not needed.


Monochrome CMOS Sensor : I'm assuming point objects like stars also throw out different wavelengths and Mono will help collect more starlight in shorter times? 

Backlit Sensor: I am assuming it will also help collect more starlight?

Small Chip : I am going for very, very narrow starfields ... so FOV has never been an issue for me. 

High well Depth: So that I do not oversaturate my images with brighter stars

Uncooled camera: I'm not going for diffused objects. Until now, stars always stand out pretty obviously for me, no matter if I have the cooling on or off. Especially when I select best pixels during stacking and then invert the image. I'm quite sure going 1 or 2 mags lower will be okay for me, with the noise.


Are the above choices correct? 


Finally, is there anything which can help with atmospheric seeing to resolve fainter stuff ? I usually always image objects above 50 degrees. Will an ADC help me get fainter stars?


I will really appreciate your support with this. Thank you. 




Edited by Agreegator, 23 September 2021 - 01:15 AM.

#2 pejorde


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Posted 23 September 2021 - 01:36 PM


Going for faint stars (or asteroids or quasars or other tiny objects) means putting as many photon as possible into as tiny a star image as possible, and a camera that detects as many of those photons as possible.


Regarding camera, you should look for high QE and low noise, and avoid any filters (thus, yes, monochrome is preferred to color). Cooling reduces noise, so may improve your chance of bringing faint stars out of the background noise. Nothing else matters, really. No need to be concerned with oversaturating faint stars!


What else you can do: Precise focus and collimation is important to concentrate those photons into a tiny point. As is good guiding, Long integration time goes deeper. Also, wait for a steady, transparent sky. And be sure the telescope has cooled to ambient temperature, or pack the telescope in reflextic or similar.


I'm note sure how deep a 6" can go. With a 10" I've reached about mag 20.

Good luck and please report back!

Per Erik

#3 RazvanUnderStars



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Posted 23 September 2021 - 04:20 PM

The other factor is going to darker sites (if applicable). Obvious, I know, but effective. Each difference of one magnitude in the sky brightness means a difference of 2.5 times in integration time to achieve the same SNR. Nice comparison at https://skyandtelesc...its-dark-skies/

#4 Ron (Lubbock)

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Posted 23 September 2021 - 04:45 PM

With my C11 EdgeHD and a low read noise camera, I am quite sure magnitude 21 is within reach.  Magnitude 20 is easy, and most of my images get there even from my Bortle 4/5 backyard.  The camera I used for these tests was purchased in 2016 and has higher noise levels than modern CMOS cameras.


In my opinion, you want large aperture, low read noise, and the darkest skies you can get.

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