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Stuf1978

First astrophotograpy attempt (M42 content) advice wanted

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Hi all, newbie alert. Although I'm pretty competent in regular photography a long term interest in anything space related has led me to try out some astro photography. So I've bought a sky watcher star adventurer in the last couple of weeks and my first target was the obligatory M42. Here's the resulting image from my first session:

Canon 80d with 70-300 sigma APO lens

42 lights at 300mm F5.6 30 secs ISO 800

12 darks 

No flats no bias

Stacked in DSS and processed in CS3

Autosave001_zpsucp1u0fz.jpg

Pretty happy for my first attempt but there are issues with it. Some of the stars are looking a little elongated which I suspect was down to polar alignment. I also think it lacks detail and is a little noisy. 

What I'm after is advice on how to improve it? Is it simply a case of adding more data and the addition of flats and bias frames?

Oh it was also taken from my garden in a pretty light polluted area. 

Thanks in advance 😁

Edited by Stuf1978
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Ah yes, the bottomless pit of Astrophotography. You have identified some issues. The doughnut appearance of the stars in your image is usually indicative of poor focus. If your camera has live view focus on a bright star at 10x zoom then lock the focus and zoom adjustment somehow. Zoom lenses can ‘creep’ so they need to be locked. This target has a high dynamic range so requires a range of exposure times to avoid blowing out the core of the trapezium. You can blend the images later during processing. 

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Hi. Good effort.

Have a look through the light frames. There maybe some that are out of focus or drifted; take those out before you stack.

It looks like the camera is tilted; better focus at the bottom than the top. Is the camera to lens mount good?

With a dslr, probably better to lose the dark frames and stack -with that sigma clip thingy-  using bias and flat frames only. There should be sufficient tracking error to emulate some sort of dither.

FWIW, I've never had much joy with zoom lenses, especially at the far end of their range. For a small outlay you could get a fixed manual 300mm e.g. this one.

HTH and hey, well done. You're on your way:)

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55 minutes ago, Stuf1978 said:

Pretty happy for my first attempt but there are issues with it. Some of the stars are looking a little elongated which I suspect was down to polar alignment. I also think it lacks detail and is a little noisy. 

What I'm after is advice on how to improve it? Is it simply a case of adding more data and the addition of flats and bias frames?

Oh it was also taken from my garden in a pretty light polluted area. 

Thanks in advance 😁

To combat noise, more exposure or longer exposures, 30secs at f/5.6 is not very long.

Flats will certainly help, darks may not help as modern Canon's have good on sensor dark current suppression.

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Good effort but I agree that focus looks out.

Be aware that at 300mm your system is working at 2.56 arcseconds per pixel. This is a thoroughly 'telescopic' resolution and certainly in 'serious mount with autoguiding' territory. For comparison, it's a considerably higher resolution than our Takahashi FSQ106/CCD rig which works at 3.5"PP.

In reality this means that tracking error will probably not allow you to get anywhere near to resolving detail at that scale. By bringing the focal length down by a long way your level of real captured detail would be unaffected and you'd have a far wider field of view. I'd be thinking of working at maybe 5"PP or more on the Star Adventurer to start with.

I used this calculator which you might find helpful: http://www.12dstring.me.uk/fovcalc.php

Olly

 

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Thanks all, that's given me a lot to think about. So in summary if I try and reign in the focal length a bit, more light frames with different exposures, get shot of the dark frames and add bias and flats that should improve things a bit?Also try and improve focussing, I did use live view to focus but should have probably used the zoom function to try and nail it down. 

I do realise I'm limited by the lens, but a better telephoto lens is on the cards for sometime this year. Also been looking at a small refractor (skywatcher ED72) that looks as though it'll work pretty well with the star adventurer and can also be guided eventually. 

The camera was mounted to the adventurer with a ball head on the star adventurer bracket and seemed pretty secure, there is the chance the lens could have creeped over time so I'll look at someway of locking it out to maintain focus. 

Thanks for all the help, I can see this being expensive 😂

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