Hello Dalia, Antoine,
As you know from a previous post concerning collimation, I'm using an Orion 8 Astrograph like you. After one my latest sessions, I noticed in the images that the diffraction spikes of the spider vanes were not perpendicular.
I checked the scope during daytime over and over again and the spider vanes are perpendicular in the tube, just one was a little tilted (which was easily fixed with the knobs to tighten them), but they are perpendicular.
I've been breaking my head about this until I saw a picture of your setup with the Orion 8. You use a dovetail that is much longer than the one that comes with the scope, and so the distance between the tube rings is much wider than in my setup with the default Orion dovetail; in my case with the DSLR, coma corrector, guide scope and guide camera all at the top, the tube has been shifted completely forward in order to obtain balance. So I start to suspect that in some positions (I was imaging M52, which at the time - mid december - was almost in the zenith) there is some torsion on the tube; and seeing you're Orion 8 setup, a longer dovetail might overcome this. Now my 2 questions:
- what dovetail are you using
- with a longer dovetail the camera can no longer "hang down" in the home position - which is said the best position to obtain balance, so how do you obtain balance.
Thank you very much for your advice!
g.
FSDG
Geert,
That's really sad to hear. I (Antoine) grew up in the North of France, one hour away from Belgium, and I totally understand. I do not know if I would be able to be an happy astrophotographer there 😔
A dew heater is crucial for sure. I hope you will get some clear skies, maybe in Spring and Summer..
Hi Geert,
Wow! I did not expect that. I have never seen this issue before and I have to admit I'm a bit clueless here.
To me, at first glance, it looks like it is maybe dew? Although I wouldn't really be sure as we never experience dew in Vegas.
I asked a few members of the Las Vegas Astronomical Society and showed them your image, they're also confused as to what it could be but they also wonder if it could be dew or an internal light reflection (like a shiny screw reflecting on the mirror) although it does sound strange.
I would suggest three things:
- Ensure it is not a dew issue (image on a very dry night or use a dew heater. Also make sure the coma corrector looks clean.
- Check for any possible light reflection
- If the issue still occurs after checking the two above, I would directly contact the manufacturer (in your case Orion) as I am guessing they are expert and will know for sure what causes this.
If you do find out what the issue was, please let us know!
Good luck!
Hi again geert,
I am really sorry I completely missed your reply and just saw it now, sadly the link has now expired :/
Depending on how your stars look on the edges it could be tilt or backfocus issues but those usually don't affect the center of the image 🤔 Maybe you can upload a JPG picture here? Unless it is too blurry then if you don't mind please upload on WeTransfer again and I'll be sure to check this post regularly! 😀
Hello,
thanks for your reply; you can find a stacked result (with APP) here: https://we.tl/t-jB7gpyQ8XS . I did not take any flats as the purpose was to see if the problem was still there after a couple of corrections (but that you will have guessed looking at the image 😉 ). There is some indication at the edges that the collimation is not perfect (as from previous post, I just cannot get this secondary mirror collimated), but the problem of the non-perpendicular diffraction spikes is also visible in the center of the image. An other weird thing is that the "horizontal" diffraction spikes show a light refraction, which makes me suspect there's an optical problem as well.(comma corrector???).
Please don't go hard on me concerning the quality of the image, I'm just starting astrophotography and thank you very much for looking into this.
Kind regards,
g.
Hey Geert,
Hmm that is really strange. I'm not sure what dovetail you have but the one that came with our telescope is the same one we use in our videos (unless you watched a video where we use the MyT mount in that case we use a Losmandy style dovetail (I think it's this one: https://bit.ly/38ph2SJ ).
If you have an image I could look at maybe I could answer better, but I haven't heard of this issue before 🤔Usually issues with diffraction spikes mean bad collimation, but your reasoning sounds like it is possible as well.