Where did I go wrong

[DavidH]

Hi all,

Have taken my first autoguided images of M42 last night and am somewhat disappointed. Would appreciate some constructive criticism. The problems with this image as I see them as follows:

1. Too much background light from moon, haze etc.
2. Not enough exposure (related to 1)
3. Vignetting

Image details:
Exposure: 3x30 sec & 1x30sec dark
Camera:Canon 10d
Scope: ED80
Autoguiding: Toucam/K3ccdtools
Guidescope: Tasco 50mm refractor
Mount: gm-8.

Do I need a flat frame to combat the vignetting, or should I try to make the light path wider?

Thanks in advance for you help,
David.

[leon]

Hi David,

I'm no expert by any means, and have only picked up a lot of good tips from the experts on this site.
Just looking at your image i feel that the light pollution was a real draw for the image, and also you probably need to take at least the same amount of darks as you do your images.
Also a 2'' T adapter would certainly help with the vignetting, other than that the guiding looks fine.

I think the Moon probably let you down with this one, maybe a light reduction filter may help as well, but i'm far from an expert.

Cheers leon

[5ash (Philip)]

looks like you have quite a few dust particles somewhere close to your sensor or on your sensor , i can see at least a dozen areas on the photo where they show up . a master flat will remove these and correct the vignetting,you also need to take multiple photos and stack them to improve the the signal to noise ratio, and take some darks to remove in camera noise. sky light pollution is as leon points out your other problem. apart from that the tracking , composition and focus look good .wait until the moon is out of the sky and you should get some great photos.
regards philip

[Dennis]

Actually that's a good image for a 1st effort - well done. Flat Fields will help get rid of the vignetting. I usually take between 3 and 6 Dark Frames and then stack them for a "master" Dark which improves the dark frame subtraction.

The vignetting seems off centre – was the camera mounted off-axis somehow, or is that a result of cropping the original image?

The noise or grain in the image is more than likely the result of only stacking 3 exposures. Try 20 or 30 for better results.

Cheers

Dennis

[rat156]

Hi David,

It's not that bad, really. But...
You really need to take some flats, set up early and take some sky flats.

I took the liberty of creating a synthetic flat and subtracting it from your image. Real flats and division would work better. The tracking and focus looks good though.

Keep at it, it's not an overnight process.

Cheers
Stuart

[DavidH]

Hi All,

Thanks for your replies.

Your suggestions mainly echo my own thoughts but had not noticed the dust spots, although they are quite obvious to me now. Thought that the moon was the main culprit, but was surprised how much vignetting there was. Don't know why the vignetting is off centre. Could this be collimation?

As for the number of exposures, would have taken more but ran out of time and laptop battery - will have to remedy this next time.

Flat frames - a few questions here. Can I take a flat frame by setting up my laptop with a full white screen and taking a shot of that? Would be easier than creating a lightbox. How do I create an articicial FF?

Still lots of learning curve left methinks.

Regards and Thanks,
David.

[rat156]

Hi David,

Artificial flat frames are sort of OK, but much better to take some real ones. I'll make an assumption here, so correct me if I'm wrong, but the camera to scope orientation can't really change. If you've got a standard T-adapter then that screws into the back of the scope, then bayonets into the camera. This makes it much easier to take flats as the cam to scope orientation can't change. You'll have to spend about five minutes one day to take some sky flats. There are many references to how to take them, even some here on IIS. If your camera orientation can move, put some reference marks on the adapter when you've got the cam in about the right position, then you can go back.

For the dust motes it doesn't really matter as they move with the sensor. But for the uneven illumination it matters. BTW I have an ED80 as well, the illumination from mine looks pretty much the same as yours, slightly off centre, so I wouldn't worry about it.

The flats should allow you to have an even light pollution gradient, which is much easier to correct out than the radial one you have now.

Cheers
Stuart

[DavidH]

Thanks Stuart,

Currently am just using a 1.25" T-ring adadapter which screws into the bayonet adapter on the camera, so the orientation is not fixed. Will have to set up some sort of index. Nice to know that your ED80 is showing off centre illumination too, so I won't bother chasing that.

Regards,
David.