M42 in rather difficult conditions

[vlaiv]

Hi all,

As this is my first post, a bit of introduction is in order. My name is Vladimir and I come from Serbia. I entered into astronomy hobby about year and a half ago.

I wanted to share this image of M42 that I took a couple of days ago, and to be honest, I would appreciate any feedback regarding quality of image and technique used.

Equipment used: HEQ5 (eqmod + usual goodies), Skywatcher ST 102/500 achromatic refractor (imaging scope), ASI185MC (imaging camera), IR/UV cut filter, wratten #8 yellow filter, DIY aperture mask (66mm, effective f/ratio - f/7.5). Unguided exposures.

Data: 9 mosaic segments, 36x10s light frames for each segment, 64 dark frames, 256 bias frames

Conditions: LP - red zone (usually around 4 mag NELM) , Moon at 94.3% positioned just above Orion and bit to the left.

Software and processing: DSS stacking, ImageJ for background calibration, mosaic and size reduction (x3) and Nebulosity4 (white balance and digital development). No noise reduction and purple halo removal was done.

OK, after some trouble trying to insert image into post, here is jpeg version in attachment. Full version can be found at:

image in png format

[wimvb]

Welcome to the forum.

Very nice image. I've been looking into ZWO cameras to replace my all too noisy Pentax for AP. It's nice seeing images with the ASI185MC. People report on amp glow with this camera. What's your opinion? Has this been a problem?

[laudropb]

Welcome to the SGL. Nice image.

[vlaiv]

2 minutes ago, wimvb said:

Welcome to the forum.

Very nice image. I've been looking into ZWO cameras to replace my all too noisy Pentax for AP. It's nice seeing images with the ASI185MC. People report on amp glow with this camera. What's your opinion? Has this been a problem?

Well, regarding ASI185mc, I did not get to test it enough, neither do I have much experience, but I can say that I'm very pleased so far. I decided to get it for deep sky work after some experimenting with QHY5IILc in deep sky. I like working with small sensor size because this helps avoid problems with coma, vignetting and field curvature. This particular cmos sensor has decent well depth (22k), 12bit ADC is a bit limiting, but I tend to restrict myself to large number of short exposures (for some reason I decided that 2min exposures would be about max for my LP conditions). Read noise is good also. There is some amp glow, this particular sample has it along 3 edges, and it is more pronounced on high gain settings (which leads me to believe it is rather fixed in nature and therefore can be subtracted with darks). Take look at this image, it is 30s dark frame at 35 db gain (very high gain)  at the room temperature (from initial test when I got the cam), to see what kind of amp glow could be expected.

Above image also had tiny problem with amp glow, and being a mosaic that was rather obvious and difficult to remove algorithmically (standard amp glow removal looks at the edge of image). I guess it was due to temp difference between light and dark/bias frames (I did darks and biases at the end of the session, with a minute or two of delay, while I parked the scope and fiddled with equipment and it was about -6C at that time - temp was falling from -4C when I started setting up for shooting). But it was so close to noise floor and easily processed out by means of digital exposure settings / min values.

Bigger problem with the image are dust specks shadows. I did not take flat frames, but as it turned out there were about a dozen dust specks on camera glass cover (easy to remove from glass cover, difficult to remove from image ). Two of them are clearly visible in nebulosity.

 

[wimvb]

This confirms what others have reported (Cloudy Nights forum).

The past few days I've seen some impressive imaging done with these small marvels, sometimes using standard DSLR lenses and short exposures.

http://www.cloudynights.com/topic/522643-m43-c11-asi224mc/

It also seems that ZWO is working on the amp glow problem. They have come out with a software "fix" that was implemented in SharpCap or FireCapture.