M42 breaking the imaging rules (taken in March 2023)

[IDM]

I was messing around with my Tal100 achromatic scope earlier this year just to see if I could get get it setup with a QHY183C camera in order to possibly do some lunar or planetary imaging. All seemed well and I was able polar align in Sharpcap and platesolving worked. I then wondered what would happen if I tried to capture M42. I didn’t expect much as I had no guiding and the pixel scale was all wrong. The Tal has a focal length of 1000mm and the QHY183C has 2.4uM pixel size so I was significantly oversampling. As I was only doing experiments and Orion wasn’t very high in the sky (Images were taken on March 7^th) I only took 10 subs. I reckoned that with the lack of guiding I might get away with 30 second exposures and a gain of 10.

On checking the subs, 2 were discarded due to satellite trails and so I stacked the remaining 8 (a total of 4 minutes integration time) with 30 darks, 30 flats and 30 dark-flats. The result was processed through Siril including the new Starnet star removal and reintegration feature (Siril 1.2.0-beta2).

Whilst the image isn’t brilliant I was rather shocked at how well it turned out give oversampling, no guiding and 4 minute integration time. I know M42 isn’t too challenging but I think it shows that whatever equipment you have it can be worth having a go at some DSO’s.

I will be interested in people’s comments.

Thanks for looking

Ian  

[vlaiv]

I think that F/10 or so 4" refractor can be really nice beginner imaging scope.

Drawbacks are - chromatic aberration, obviously, but there are some filters to help with that. It's a bit long so better mount is needed.

As far as over sampling go - you can (and should) bin your data, even after capture in software.

 

[Rodd]

3 hours ago, vlaiv said:

chromatic aberration,

Actually, the longer the focal ratio the less evident the chromatic aberration will be.  It's much more difficult to make an apochromat at F3 than F15.  I'd say the downside of a F10 4' scope is speed.  Yes, you can bin, but I think I would recommend a beginner start with an F5-F6 scope instead of an F10 scope that requires binning (and a bigger mount!)

[vlaiv]

1 hour ago, Rodd said:

Actually, the longer the focal ratio the less evident the chromatic aberration will be.  It's much more difficult to make an apochromat at F3 than F15.  I'd say the downside of a F10 4' scope is speed.  Yes, you can bin, but I think I would recommend a beginner start with an F5-F6 scope instead of an F10 scope that requires binning (and a bigger mount!)

You are of course right - nicer beginner scope is certainly F/6-F/7 ED doublet or F/5-F/6 tripled, but what I really meant (and did not say) is:

nice beginner imaging scope on a budget

Most people starting out in a hobby don't want to rush in with large cash and some even can't afford whole setup if it includes scope that is 500-600 euro + by itself (as there are a lot of extras to be purchased as well and total quickly adds up).

We tend to recommend 5"-6" newtonian in budget role or perhaps 72mm ED scope.

There are however abundance of second hand 4" refractors - as most visual observers move to ED glass once budget allows - and sell on their beginner refractor.

At F/10 - CA is much easier to manage as you've also noted. I did not mention, but another weak point with such budget scope is focuser. Most require some TLC before they can be utilized for imaging, and some are simply beyond help.

BTW, I have 4" F/10 scope waiting to be put to test as imaging scope in various roles - from planetary to long exposure imaging, just need to get around to doing it.

[ollypenrice]

7 hours ago, IDM said:

I was messing around with my Tal100 achromatic scope earlier this year just to see if I could get get it setup with a QHY183C camera in order to possibly do some lunar or planetary imaging. All seemed well and I was able polar align in Sharpcap and platesolving worked. I then wondered what would happen if I tried to capture M42. I didn’t expect much as I had no guiding and the pixel scale was all wrong. The Tal has a focal length of 1000mm and the QHY183C has 2.4uM pixel size so I was significantly oversampling. As I was only doing experiments and Orion wasn’t very high in the sky (Images were taken on March 7^th) I only took 10 subs. I reckoned that with the lack of guiding I might get away with 30 second exposures and a gain of 10.

On checking the subs, 2 were discarded due to satellite trails and so I stacked the remaining 8 (a total of 4 minutes integration time) with 30 darks, 30 flats and 30 dark-flats. The result was processed through Siril including the new Starnet star removal and reintegration feature (Siril 1.2.0-beta2).

Whilst the image isn’t brilliant I was rather shocked at how well it turned out give oversampling, no guiding and 4 minute integration time. I know M42 isn’t too challenging but I think it shows that whatever equipment you have it can be worth having a go at some DSO’s.

I will be interested in people’s comments.

Thanks for looking

Ian  

That's nice and specialized processing could take it still further. The real problem, though, is that this small part of M42 is far, far brighter than any other deep sky object I can think of.  To be specific, in my own M42 I shot this region in 11 second exposures, the area around it in 50 second exposures and the rest in fifteen minute exposures. The Trapezium region is not your typical DSO!

Olly