Grainy and with grid

[George Gearless]

Hey guys.

I recently lost my financial mind and bought an equatorial mount, Skywatcher EQM 35-pro :). I am terribly pleased with it allthough my better half displayed a somewhat less enthusiastic demeanor when I broke the news ( I took cover behind the couch and threw small pieces of chocolate at her, until she calmed down).

Anyway, cue crappy weather for 3 weeks but then I finaly got a quick run at M42. Only 7 lights and darks, 150secs, ISO I forget, EOS 7 Mark I. Stacked in DSS and enhanced in Startools. Yeah, I went a bit overboard on the red, but I wanted to see the clouds on the right side a bit clearer. Plus, I'm still learning Startools. It was a trade off:

 

Given I'm using a 127mm Maksutov, I'm not sure I can ask for much more. But it does seem quite 'grainy'. I'm also having trouble keeping the background dark. It's very red.

 

A week or so later I gave m31 a go. The result was discouraging :(. Take a look:

 

Incredibly 'grainy' and now with a distinct black-lined grid across the whole picture. 

I pressume the grid has something to do with the sensor on my camera. But how can I avoid it?

Secondly, I realize that my telescope is far from ideal for DSO's. Is the grainy quality just something I'll have to deal with, with this telescope? Or do you have a tip or two that'll help minimize it? And if you suggest getting an apochromatic refractor, my girlfriend will kill you :)!

 

George

 

[Demonperformer]

I think your second photo is a result of major over-processing, which is an art in itself. Other, more experienced souls, will no doubt either confirm that or refute it, but it looks a lot like some of my pictures when the processing has "got away from me". I find this happens when it has started to go wrong and, rather than going back, I try to correct it by further processing steps which usually make it worse. As a result, I have started the habit of saving the result of my processing after each step. All these intermediates can be deleted when I have a finished product with which I am happy, but if I find I have gone down a dead-end, I can go back to a point where I think I went wrong, rather than having to start again.

Which is all a long-winded way of saying that I guess there is a better image hidden in your original data, but you are going to need to reprocess it from scratch to find it ...

[George Gearless]

9 hours ago, Demonperformer said:

I think your second photo is a result of major over-processing, which is an art in itself. Other, more experienced souls, will no doubt either confirm that or refute it, but it looks a lot like some of my pictures when the processing has "got away from me". I find this happens when it has started to go wrong and, rather than going back, I try to correct it by further processing steps which usually make it worse. As a result, I have started the habit of saving the result of my processing after each step. All these intermediates can be deleted when I have a finished product with which I am happy, but if I find I have gone down a dead-end, I can go back to a point where I think I went wrong, rather than having to start again.

Which is all a long-winded way of saying that I guess there is a better image hidden in your original data, but you are going to need to reprocess it from scratch to find it ...

Ok, that kind of makes sense. Thinking back, I probably spent a little too much time trying to improve the picture that I actually made it worse. I guess I'll have to learn when 'enough is enough' :).

Thanks

[michaelmorris]

The grid pattern looks like an effect known as Fixed Pattern Noise.  This is caused by imperfections and artefacts in the process of rows and columns of the camera chip during recording and reading out the image.  Using 'Dithering' during image capture and dark frames calibration during image processing can both help smooth out many of these artefacts.

https://en.wikipedia.org/wiki/Dither

http://dslr-astrophotography.com/dithering-optimal-results-dslr-astrophotography/

[Alien 13]

I agree with whats been said but ultimately your problems arise from lack of data, this usually means that processing ends up being more aggressive.

Great start though and who would have guessed that a Mak can do DSO..

Alan

[wimvb]

With a Mak at its native f/12, you have very slow optics that need long exposure times. Your M42 image shows this; normally at 150 s the core will be overexposed beyond rescue. Yours is actually very nice. But that also means that dimmer targets will be grossly underexposed at those settings. And that's what happened with your M31 image. The signal is too weak to clear the read noise floor. More exposures can improve this somewhat, but you really need to increase exposure time.

A f/12 Mak is a challenge for dso imaging, but if you use it for bright targets, you should be able to pull some very nice images out of it. For larger targets you can use a telephoto lens on your eq mount. The Andromeda nebula is very nicely framed in a 300 mm lens.