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HyperStar - Advice on Camera Settings

Starizona HyperStar 6 v4 (HS4-6) ZWO ASI585MC Pro CMOS Acquisition
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Jean-David Gadina avatar
Jean-David Gadina avatar
I just bought and received a Starizona HyperStar for my Celestron Evolution 6.
I'm using a ZWO ASI585MC Pro, shooting from a Bortle 6 area.

With the current weather conditions, I could only test it once, during a two-hour session interrupted by clouds.
I was wondering what camera settings I should change when using the HyperStar compared to my usual setup to take full advantage of its fast f ratio.

Usually, I set my camera to unity gain (252), offset 7, bin 1x1, and take exposures of about 1 to 5 minutes at f10 or f6.3, using a reducer.

What would you recommend for the HyperStar at f2?
  • Is it worth lowering the gain?
  • Should I lower the offset?
  • What exposure time would you recommend?
  • Is it better to take more exposures but shorter ones or keep the same time and gather more light?

I would appreciate any advice from experienced HyperStar users.
Clear skies!
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Silaenoz avatar
Silaenoz avatar
Hi, im very interested in this topic since i plan to switch to the same system, and owning a 585 pro too. 
No advice though, but you should precise what kind of filter youre using most of the time, it will obvioulsy greatly affect the time exposure needed with your fast system.

Regards
Astro With RoRo avatar
Astro With RoRo avatar
This can be a rather complex topic, but in short: yes you will want to adjust settings compared to your other setups.

Shooting at f/2 will saturate your camera's pixels 10 times faster than at f/6.3 and 25 times faster than at f/10. As such (and assuming filters, etc. all remain equal) you can simply reduce your exposure time by a factor of 10 and receive an equivalently exposed sub. Alternatively you can drop the gain to increase your pixels full well depth which will increase how long you can expose for before saturating pixels. The 585 has most dynamic range at 0 gain (~12.5 stops), and that drops to ~11 stops at the high gain conversion (unity gain is actually 198, but that's a different story and probably not what you're after).

Ideally you want to expose for as long as you can without clipping any data. An easy way to check for this is to look at your images without stretching. If you can make out obvious stars then you're probably clipping and losing data on and around your stars.

Based on your gear & location your minimum exposure length at 252 gain is around 1 second (anything above that will swamp read noise just fine). For 0 gain your minimum exposure time is 24 seconds to swamp read noise.

Assuming your current images are exposed well, there's 2 things you can try.
  1. Drop exposure time by 10 / current exposure time and keep gain at 252.
  2. Drop gain to 0 but keep exposure time at the same 1-5 minutes.


Both of these will continue to swamp the read noise and sky glow. You can of course increase exposure time as you see fit from the above mentioned, just check for clipping in stars.
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