ASI 585mc for 8" F5 Newt for DSO: good idea?

[MichaelBibby]

I recently bought a belt modded Heq5 pro mount and 8" f5 (1000) Newtonian telescope and am wanting to get into astrophotography (I have previously owned an 8" Dob, so I am not completely new to astronomy, and I understand the need to maintain good collimation). I'm more interested in DSO than planetary imaging.

Now, with this setup I am probably going to be limited to relatively short exposures owing to the fact that my scope is pushing the weight limits of my mount, that, and the fact that I'm not using a guidescope at pretty high magnification. My main interest is imaging galaxies, and nebula.

Given these restrictions would the zwo asi585mc be a good option? I understand its not ideal (my first preference would be for the 533mc, which, besides being cooled also has a sensor twice the size of the 585), and that its a 'planetary camera', but I have seen people getting great results with it using short exposures on DSO with smaller apertures and comparable focal lengths. Is there a better camera for the same price that you would recommend for my setup?

Any help is greatly appreciated.

Edited September 30, 2022 by MichaelBibby

[Vulisha]

Concider PlayerOne Uranus C, as it has passive cooling, and active can be bought as addon. Same sensor. 

 

533 would probably be better due to bigger sensor, but regarding capability 585 has same chip performance as I investigated 

[dph1nm]

The 585 has 2.9um pixels, so about 0.6". A touch over-sampled unless you have very good seeing. The 533 is a bit better at 3.76um, but there really aren't many (cheap) cameras matched in pixel size to >=1000mm FL imaging, so you are always going to have to compromise.

NigelM

[MichaelBibby]

I should have said that I live under (about) Bortal 3-4 skies.

(Thanks for the replies, I'm learning alot as I go).

Edited September 30, 2022 by MichaelBibby

[MichaelBibby]

I just discovered this online tool which matches your focal length with ideal pixel size under various seeing conditions:

https://astronomy.tools/calculators/ccd_suitability

This seems to indicate that the 2.9um pixels might make a good match for my focal length in good seeing conditions, but in worse seeing conditions it would tend to fall on the side of oversampling, and from what I understand, oversampling is less forgiving of guiding problems.

Edited September 30, 2022 by MichaelBibby

[Clarkey]

Without guiding you are always going to be oversampling at 1000mm FL. Your tracking needs to be about half your image resolution which is certainly not going to be the case with a large newt on an HEQ5. Realistically you will be doing well if you can get anywhere near 2" per pixel. I image with a AZ-EQ6 and I will aim for about 1" per pixel with guiding and good seeing . Typically it is normally nearer 1.5" depending on the quality of the images in terms of FWHM of the stars.

If you bin you data you will get a faster system that will help alleviate some of the tracking errors and help with shorter exposures. Depending on where you are good seeing is not common is the UK so the pixel scale is a bit irrelevant in terms of seeing when you are not even guiding.

[MichaelBibby]

Seems like the Sony a6000 might be a good choice-- its pixel size is 3.88um (which is really in the 'perfect' range for my focal length, and more forgiving of tracking errors, especially if using under 30s exposures).

Or if I were to stick to exposures under 30s would that largely mitigate most tracking problems, and produce good results with the 585mc? I wonder how these camera's would compare with that sort of exposure time...

[Adam J]

On 30/09/2022 at 11:19, MichaelBibby said:

I recently bought a belt modded Heq5 pro mount and 8" f5 (1000) Newtonian telescope and am wanting to get into astrophotography (I have previously owned an 8" Dob, so I am not completely new to astronomy, and I understand the need to maintain good collimation). I'm more interested in DSO than planetary imaging.

Now, with this setup I am probably going to be limited to relatively short exposures owing to the fact that my scope is pushing the weight limits of my mount, that, and the fact that I'm not using a guidescope at pretty high magnification. My main interest is imaging galaxies, and nebula.

Given these restrictions would the zwo asi585mc be a good option? I understand its not ideal (my first preference would be for the 533mc, which, besides being cooled also has a sensor twice the size of the 585), and that its a 'planetary camera', but I have seen people getting great results with it using short exposures on DSO with smaller apertures and comparable focal lengths. Is there a better camera for the same price that you would recommend for my setup?

Any help is greatly appreciated.

Honestly I think that would be a great combo for galaxy imaging at high gain / short exposures ~1s to mitigate seeing. 

[MichaelBibby]

26 minutes ago, Adam J said:

Honestly I think that would be a great combo for galaxy imaging at high gain / short exposures ~1s to mitigate seeing. 

I didn't think such short exposures were possible with the 585mc at gains with low s/n. My understanding is that the ideal gain setting for the 585mc is about 252 (from what I've read). I was thinking more along the lines of 30 second exposures? Would the a6000 produce better results at these sort of exposure times? Could I expect reasonable tracking with my setup over 30s exposures? (Note: I do intent do 'hypertune' my mount at some point, and really squeeze the most out of it).

[wimvb]

With an 8" scope on an heq5, you're pushing the limit, even with guiding. The large scope is like a sail in the wind, so I think that the choice of camera is a minor concern. If I were you, I'd look into guiding first, preferrably an off axis guider.

That being said, 1s exposures are doable, but you need to take lots of them, think thousands.

http://www.astrokraai.nl/viewimages.php?t=y&category=7

[MichaelBibby]

Fortunately where I'm building my pier will be relatively shielded from the wind so that shouldn't be too much of a problem 

[MichaelBibby]

I've created a separate thread to address the specific question of 585mc vs a6000 for my setup here:

 

[Adam J]

10 hours ago, MichaelBibby said:

I didn't think such short exposures were possible with the 585mc at gains with low s/n. My understanding is that the ideal gain setting for the 585mc is about 252 (from what I've read). I was thinking more along the lines of 30 second exposures? Would the a6000 produce better results at these sort of exposure times? Could I expect reasonable tracking with my setup over 30s exposures? (Note: I do intent do 'hypertune' my mount at some point, and really squeeze the most out of it).

You would use it at gain 400 but the player one version looks better for this type of imaging. As above though 1000s of subs are required. 

[MichaelBibby]

2 hours ago, Adam J said:

You would use it at gain 400 but the player one version looks better for this type of imaging. As above though 1000s of subs are required. 

I suppose your talking about the 'High Gain Conversion' mode on the Uranus-C which kicks in when the iso is >180 and helps to reduce noise while preserving dynamic range.

Thanks, that might be a great option.

[PeterC65]

Both the ZWI and Player One IMX585 based cameras have High Conversion Gain mode. With the ASI585MC it kicks in a a gain of 252 and with the Uranus-C it kicks in at 180. From what I understand, the accepted wisdom is to operate the camera at a gain just above the HCG / LCG switching point as this is the best compromise between read noise (reduces with gain), dynamic range (reduces with gain), full well depth (reduces with gain) and the overall SNR of the image (increases with gain).

I chose the Uranus-C over the ASI585MC as a result of the difference in the HCG / LCG switching point. There is a longer discussion here. I've only been able to use the camera once so far, so I'm not yet decided on the pros and cons, but the Uranus-C is a well-built camera and I prefer the hexagonal body as it allows me to know how the sensor is aligned.

 

[Vulisha]

And mind you, do not forget that you can always use binning, to increase size of your pixel. You can even use it in post-processing if you see tracking errors 

[MichaelBibby]

13 hours ago, PeterC65 said:

Both the ZWI and Player One IMX585 based cameras have High Conversion Gain mode. With the ASI585MC it kicks in a a gain of 252 and with the Uranus-C it kicks in at 180. From what I understand, the accepted wisdom is to operate the camera at a gain just above the HCG / LCG switching point as this is the best compromise between read noise (reduces with gain), dynamic range (reduces with gain), full well depth (reduces with gain) and the overall SNR of the image (increases with gain).

I chose the Uranus-C over the ASI585MC as a result of the difference in the HCG / LCG switching point. There is a longer discussion here. I've only been able to use the camera once so far, so I'm not yet decided on the pros and cons, but the Uranus-C is a well-built camera and I prefer the hexagonal body as it allows me to know how the sensor is aligned.

 

 
Thanks Peter, I have been following that thread. I guess what I am realizing is that what I am wanting to do is EAA (live view, live stacking, short exposure times, etc.,). And it seems like the 585 might be a good fit ('compromise') for my setup (whereas the a6000 would cause me a lot of headache's owing to Sony's incompatability with Sharpcap).
But I thought I saw you say somewhere in that threat @PeterC65 that the P1 version would have better s/n performance than the ZWO version, is that still your assessment? For very short exposures at high gain would you recommend one over the other?

Edited October 3, 2022 by MichaelBibby

[PeterC65]

7 hours ago, MichaelBibby said:

 
Thanks Peter, I have been following that thread. I guess what I am realizing is that what I am wanting to do is EAA (live view, live stacking, short exposure times, etc.,). And it seems like the 585 might be a good fit ('compromise') for my setup (whereas the a6000 would cause me a lot of headache's owing to Sony's incompatability with Sharpcap).
But I thought I saw you say somewhere in that threat @PeterC65 that the P1 version would have better s/n performance than the ZWO version, is that still your assessment? For very short exposures at high gain would you recommend one over the other?

I posted the SharpCap sensor analysis of my Uranus-C camera on the other thread and I'd say it is almost identical to that of the AMC585MC apart from the HCG / LCG switching point and at gains of 600+ when the Uranus-C read noise dips below 0.7e. This last point is moot as the difference is tiny and may even be nothing (there is only one data point for the Uranus-C at a gain of 600 when the read noise is 0.68e). I don't think read noise is a reason to choose the Uranus-C over the ASI585MC but the HGC / LGC switching point, and the maximum gain obtainable via SharpCap may be (I can set the gain to 800 in SharpCap with the Uranus-C so that means the LCG range only 'wastes' 22.5% of the possible gain range).

I can't compare the Uranus-C to the ASI585MC without having both cameras, but I do plan to test the Uranus-C at all gain setting from 0 to 800 in intervals of 50 (and around the HCG / LCG switching point) when I get a clear night. I will post about the results.

Regarding SharpCap, I wouldn't use anything else for EEVA (which is what I do with my cameras) and so if SharpCap does not support a camera I wouldn't buy that camera. I have used SharpCap with my DSLR via the ASCOM drivers and the experience isn't as good.

 

[PeterC65]

Just thinking some more about the Uranus-C vs the ASI585MC, leaving aside the HCG / LCG switching point, I think the pros for each are:

Uranus-C

• The hexagonal casework makes it easy to orientate the sensor.
• It has passive cooling that can be upgraded to active cooling for £80.
• There is built-in tilt adjustment.

ASI585MC

• There is better UK based support, and in particular, from FLO.
• ZWO cameras are more popular than Player One, so you are more likely to get user support.
• It is slightly cheaper (currently £428 at FLO vs £480 at Starfield Optics for the Uranus-C - FLO do have a customer return for £385 though).

I think the HCG / LCG switching point is only an issue if the ASI585MC maximum gain in SharpCap is much less than the 800 it is for the Uranus-C, and I don't yet know the answer to this (@Chris has said he will check his ASI585MC).