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Hi, 
I am a complete novice and got into astrophotography in December of last year, I had some decent success using only my Canon 450D and stock 18-55mm lens. 
Since then I have purchased a telescope and mount (Sky-Watcher Startravel 102 and the AZGTe WiFi GOTO mount), which arrived yesterday. Luck would have it that the skies were clear last night and I had a go at imaging both M42 and M31 (also tried m45 tonight just to see if I could fiddle around with anything to solve it, but no luck), both of which came out pretty dissapointingly.

If someone could tell my what is is that is wrong with the star shapes in the images, and potential fixes, it would be greatly appreciated, as I don't want to waste another clear night if it is an easy fix!
I have read about coma, but also that refractors don't have this issue, so I am completely baffled.

 

Thanks in advance.

 

M45 at 1 second exposure, M42 at 20 seconds and M31 at 30 seconds.
m45.thumb.JPG.d3a5d3e2b769907a1eb86184229183f6.JPG

m42.thumb.JPG.94d5b60baa29288914f79b72ddaaeae5.JPGm31.thumb.JPG.1932741dcb5baed59ab888df7d2cc0f7.JPG

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I have no idea what might be going on - but I really like the effect!

Best warp speed I've seen so far :D

Refractors suffer from field curvature - but what ever this is - it is far too much - it should not look like that.

Can you describe your setup please? I'm wondering if there is some extra piece of glass between telescope lens and camera sensor?

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Hi

Looks like you might be using a barlow that's not needed for the ST102.

If you were using you mount and ST102 in altaz mode I expected the framing more like this

https://stargazerslounge.com/topic/228101-the-no-eq-dso-challenge/?do=findComment&comment=3776550

16102283688001.jpg.b1f081497f1d22ac6eeb3b3884126258.jpg

Through I'm on a tiddy phone screen which might have miss led my comment.

 

 

Edited by happy-kat
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1 hour ago, CCD-Freak said:

Are you using a focal reducer?  Looks like the spacing is wrong if you are.

 

 

I have no idea what this is, perhaps?

 

2 hours ago, vlaiv said:

Can you describe your setup please? I'm wondering if there is some extra piece of glass between telescope lens and camera sensor?

Sure, as I mentioned I am extremely new so this might be completely wrong but I followed a youtube guide and bought a https://www.amazon.co.uk/gp/product/B01LWJ2Z3Y/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1, which I am slotting into the diagonal with the 25mm eyepiece provided (which by the sounds of things may be my issue, but I seem to not be able to focus or even really find what I am looking at through the viewfinder without the eyepiece here). I have also tried just attatching the T-ring where the diagonal usually goes but again, I could not seem to be able to focus/see anything. I'm assuming that it may just be my ineptitude rather than anything else as to why I can only focus with the eyepiece projection? (is that what it's called?)

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7 minutes ago, Uncertainty said:

Sure, as I mentioned I am extremely new so this might be completely wrong but I followed a youtube guide and bought a https://www.amazon.co.uk/gp/product/B01LWJ2Z3Y/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1, which I am slotting into the diagonal with the 25mm eyepiece provided (which by the sounds of things may be my issue, but I seem to not be able to focus or even really find what I am looking at through the viewfinder without the eyepiece here). I have also tried just attatching the T-ring where the diagonal usually goes but again, I could not seem to be able to focus/see anything. I'm assuming that it may just be my ineptitude rather than anything else as to why I can only focus with the eyepiece projection? (is that what it's called?)

Yep, that won't work, or rather - it will work as you have discovered - it will be usable only in central part of the field of view and it will show serious issues.

You only really need T2 adapter for your camera and you should put that directly in telescope focuser. You should be able to reach focus like that if I remember correctly - I used to have that scope and I took some pictures with DSLR attached - but only daytime shots with DSLR.

Let me see if I can find a video that you can watch and see how best to attach DSLR.

https://www.youtube.com/watch?v=8w_p2vM1g-w

This shows ST120 - so bigger version but principle is the same.

With the item you purchased - you should have everything you need - you only need to use T2 adapter to canon mount, so this bit:

image.png.877904468b2a94ea783140f6a7772d5a.png

You should be able to screw that on T2 thread on back of your telescope. In order to reach focus - you'll have to wind out focuser quite a bit (see video for details).

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11 minutes ago, vlaiv said:

Yep, that won't work, or rather - it will work as you have discovered - it will be usable only in central part of the field of view and it will show serious issues.

You only really need T2 adapter for your camera and you should put that directly in telescope focuser. You should be able to reach focus like that if I remember correctly - I used to have that scope and I took some pictures with DSLR attached - but only daytime shots with DSLR.

Let me see if I can find a video that you can watch and see how best to attach DSLR.

https://www.youtube.com/watch?v=8w_p2vM1g-w

This shows ST120 - so bigger version but principle is the same.

With the item you purchased - you should have everything you need - you only need to use T2 adapter to canon mount, so this bit:

image.png.877904468b2a94ea783140f6a7772d5a.png

You should be able to screw that on T2 thread on back of your telescope. In order to reach focus - you'll have to wind out focuser quite a bit (see video for details).

Thanks so much for the knowledge and assistance, skies have clouded over now but will do it properly next time!

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Looks like you have everything you need with what you bought, just don't use an eyepiece in the extension tube.

I personally like to use a T mount (the short nose cone in your svbony bits) with the T ring (in your svbony bits). Fit these to your camera, on telescope remove diagonal, then fit the camera to telescope focuser.

If on testing on a cloudy day on distant tree or similar (NOT the sun) you might find you need to use the longer extension tube you got with your svbony bits to reach infinity focus (don't use an eyepiece).

Good luck sorting it out.

 

 

Edited by happy-kat
v for an e
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For future reference, the teardrop-shaped stars pointing towards the central focused part of the image are suffering from Coma.

That's an effect often seen (to a much lesser extent !) on both Refractors and Reflectors, and is removed by a Coma Corrector, screwed between the camera and telescope at a specified spacing to the camera sensor.

But remove the eyepiece in your case !

Michael

Edited by michael8554
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21 minutes ago, michael8554 said:

For future reference, the teardrop-shaped stars pointing towards the central focused part of the image are suffering from Coma.

That's an effect often seen (to a much lesser extent !) on both Refractors and Reflectors, and is removed by a Coma Corrector, screwed between the camera and telescope at a specified spacing to the camera sensor.

Michael

C'mon, that's no coma, that is lacewing!

image.png.41a7558c12bbc50968ffe54b237d5372.png == image.png.26cb875486159c695cc850c591195066.png

And this is what coma looks like:

image.png.ee4701d917e73a4364a7dca5b45dd904.png == image.png.db203cf3af9ee2ac3f4061d32000263e.png

:D:D :D

 

  • Haha 1
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@vlaiv It worked!
Thanks for giving me a simple fix, other sources I found had me believe that I had to spend quite a bit of money to fix it.

Clouds only cleared for around an hour for me to test and I still have to master alligning and tracking, but that's for another day.

 

Cheers.

m42_fixed.thumb.JPG.4edd6df018154094cca166e4d9f9791c.JPG

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6 minutes ago, Uncertainty said:

Clouds only cleared for around an hour for me to test and I still have to master alligning and tracking, but that's for another day.

There are a few other things that you can do to improve your image further.

At some point, you are probably going to want to remove those blue halos around stars. When you come to that point - lookup aperture masks and wratten #8 filter.

That is easy and low cost method of getting rid of chromatic aberration  - but it comes at expense of imaging time (you have to shoot more subs because aperture mask blocks some of the light), and custom white balance (yellow filter creates yellow cast that you need to remove in post processing).

 

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