M42 - First Light with ASI533MC

[Philter]

I bought an ASI533MC last year and I finally managed to use it for DSO imaging on Tuesday night. I've messed around with my DSLR before but I found it fiddly and what data I did get seemed very noisy and hard to process so I never really got far with it. 

This was also my first real attempt at guiding and I'm not sure if it's uncovered an issue with the mount (large DEC backlash).

• Sky-Watcher Evostar 80ED DS-Pro with 0.85x reducer/flattener
• ZWO ASI533MC at -15c
• IDAS D2 filter
• HEQ5 Pro

 

• 28 x 120s lights (56 mins) - I lost M42 behind trees so I couldn't get anymore data
• Darks, flats and dark flats used
• Captured with Astro Photography Tool
• Stacked and light pollution\gradient removal in Astro Pixel Processor
• Levels and curves in Photoshop (I don't know how to do much else!)
• PHD2 guiding
• Bortle 7

I know it's only a short integration time and I've probably stretched too much so there's still a lot of noise. I need to find out how I can reduce the hot pixels and the halos around bright stars  

 

Edited March 4, 2021 by Philter

[Clarkey]

For the limited integration time that is a good result. Well done!

I can't really help with the processing as I use Affinity. The only thing I would say is you can use layers to stretch the nebulosity more than the stars or use a star mask.

[Philter]

Thank you. Whatever my next target is I know I need to get a lot more data.

I'm going to have to make a serious effort in learning to use layers and masks to get the most out of my images particularly when imaging objects like M42 where multiple exposure times might be needed for different areas. Time to start looking for some tutorials!

[Philter]

One thing I completely forgot to mention in my original post but wanted to ask about is offset. I set the gain manually in APT but forgot to put an offset in my plan details. The FITS header shows an offset of 1 in my captures but I've read I should use a value of about 50.

From what I can see using an offset that's too low can cause clipping. Will I have lost some detail by not setting the offset properly?

[geeklee]

On 05/03/2021 at 09:38, Philter said:

From what I can see using an offset that's too low can cause clipping. Will I have lost some detail by not setting the offset properly?

Great start @Philter An offset of 1 does seem unusually low but it's possible the application might have registered that as a default value rather than the actual one.  I primarily use the ASCOM driver for my ASI533 and clicking "properties" for this in Apt (or any application) brings the ASCOM dialogue up and there's some built in defaults for unity gain (gain), highest dynamic range (gain 0) and lowest read noise (high gain).  This keeps things simple if you want one of those defaults as it sets the offset for you, although at a conservative level. 

[Clarkey]

I have an ASI 1600MM and I have the offset at 50 so that sounds about right. I am not sure specifically what the 'recommended' level is for the 533 though. To be honest as long as it not so high as to reduce the total dynamic range it is not too critical. I would suggest increasing it a little though to avoid any data loss.

[Philter]

5 hours ago, geeklee said:

Great start @Philter An offset of 1 does seem unusually low but it's possible the application might have registered that as a default value rather than the actual one.  I primarily use the ASCOM driver for my ASI533 and clicking "properties" for this in Apt (or any application) brings the ASCOM dialogue up and there's some built in defaults for unity gain (gain), highest dynamic range (gain 0) and lowest read noise (high gain).  This keeps things simple if you want one of those defaults as it sets the offset for you, although at a conservative level. 

Thanks @geeklee and @Clarkey

I'm using the native ZWO drive in APT and I had the "Manage gain" option ticked in the CCD settings tab. I think this means that I need to explicitly state the gain in the plan settings which I set at 100 (unity gain as far as I'm aware). I'd left the offset field blank in both the CCD settings and plan settings but I think should have set at around 50 as Clarkey says.

I guess there's not much I can do about it now but at least I'll know for next time whenever that is, ha ha.

 

Edited March 6, 2021 by Philter