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Hello there, So i took an image of the Orion nebula and after stacking and stretching i saw a line from left to right. It aligns with one of the diffraction spikes of a star however it looks like its not connected to it. I checked single frames and it's there on all of them although very faint. Do you guys think it actually is a diffraction spike this long? why did i get it? Is it bad collimation? I did star test and i thought collimation was good but i am still new at this! if its not collimation how do i get rid of it?  |
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| Nearby star that's just out of frame is my first thought. Newts are pretty bad for this. Maybe Alnitak? |
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I don’t think the line is completely parallel to the other spikes, so it’s probably a plane/satellite that is in one frame and didn’t get rejected. Edit: I missed that it’s there in every frame, that’s weird. |
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Johannes Möslein: I saw this as well, but if you look at his spikes on the stars, theres a split (indicative of a bent vane). The upper half of the split actually is pretty close, and would make sense since the star is probably a full frame away. |
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Rogue diffraction spike from either the bright star in this image (doubt it, but could happen) or from one outside the field of view. These things happen with newtonians, dont think about it too much and just live with it. These are very easy to get rid of though, if you have the tools. Open up the image in Photoshop and separate the stars from the starless layer with StarXterminator. The rogue diffraction spike can land itself on either layer, in this case i think it will go to the starless layer since it is separated from any star and so starXterminator should not think its a star spike. In any case, simply lasso tool the artifact and right click fill and choose content aware. 9/10 it goes away without any issues, and the other 1/10 times you have to be more careful with the lasso selection. |
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Brian Puhl:Johannes Möslein: So split diffraction spikes means bent vanes? thats very good to know i'll definitely check it out! |
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Downloaded the JPEG and gave it a bit of a stretch to see if there are more spikes (hope you dont mind). It looks like the diffraction spike here is from the bright star in the image, and not some out of field thing. See below, there are also extended diffraction spikes for the other 3 directions from that star (starXterminator got rid of the one you had issues with, but these other can still be seen): So split diffraction spikes means bent vanes? thats very good to know i'll definitely check it out! Could also be unsymmetric vanes. An easy way to check is to take a picture of your scope from the front with the camera dead center. If you have a bubble level built into your phone camera app then the centering becomes easy, if not, just eyeball it. Then open the image in paint and draw straight lines from one end of the spider vane to the other and you will immediately see if they are not symmetric and by how much. |
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When I had my E-180 and E-210, a split diffraction spikes was always from the collimation being off a bit, not from a bent vane. Not that you could ever bend a vane in the E-180 or the E-210. |
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Oskari Nikkinen: No problem using the image, on the contrary, thank you for going into the trouble it was very informative! I will have a look at my scope. To be honest i "messed around" with the vanes and the secondary trying to learn collimation. I was having many issues at the beginning and i solved most of them now its just fine tuning from here. My T-ring was of pour quality and had slight tilt build in it causing astigmatism, which at the time i didn't know what was the cause and i did a lot of experimenting to find out (i thought it was sensor tilt at first). Eventually i bought a new Baader T-ring which is perfect, no aberrations whatsoever now! But this is how astrophotography is i guess very slow progress. |
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Brian Puhl:Johannes Möslein: Bent might be an aggressive term, but they aren't straight. |
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| Seems very unlikely. |
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Brian Puhl: Alnitak would be too far in this frame. Maybe if he was imaging the Horsehead then sure. |
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| Excellent discussion. Nothing to add. |
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Brian Puhl: Alnitak was merely a guess. Personally I don't think it's too far... Anyways, I drew up some lines based off the spike. The only star that lines up is just outside the frame on the left. The rest of them don't really make sense. My ability to draw a straight line can be questioned here though.  |
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Hi I'm having the same problem. Did you fix it?? I also think it's something with the vanes.   I've rotated the camera and follows the spike, in Canopus. Also in Orion  Let me know please if you fix it Greets!! |
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Alejandro Navarro: As a matter of fact i have solved the issue! its very simple. Its reflections from the spider vanes. Just put some velour on the spider vanes and that's it problem solved! As i can see from your images you also have split diffraction spikes which is something i had too. For this you have to either adjust your spider vanes to be as straight as possible or upgrade your telescope and put some spiders that are machine cut and are straight with high precision. This is the one i bought for my telescope: https://www.backyard-universe.de/en/p/secondary-spider-sw150-cnc-machined Also in their tutorial about how to install the spider they have a nice explanation about diffraction spikes its quite informative as it explains about split diffraction spikes too: https://www.backyard-universe.de/en/i/installation-secondary-spider Here is how mine turned out! I hope I helped!  |
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Thank you very much pal!!!! I'll do it today!! Thanks again! |
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Hi Menelaus, you bet me to it 😃 on solving … I knew I seen that issue before, I’ve been considering getting the up grade kit. Well done |
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Putting velour on the vanes reduces any possible grazing reflections but it does a much more important thing. It makes your vanes considerably thicker. In the world of Fourier optics, making something thicker, makes it diffract light at a smaller angle, which will tighten up the diffraction pattern so it will concentrate the amount of diffracted energy into a smaller region in your image, which will make it brighter. Thinner vanes diffract less energy and spread the light over a larger area, which might be why you were having trouble in the first place; but I doubt that was your problem. Did you carefully blink through your subs to insure that there were no satellite trails in any of the subs where you saw the stray? I am almost certain that's where the line of light is coming from in your stacked image. As others have suggested, I believe that it's from a satellite trail that was not completely rejected by the stacking filters. Only a very bright star will send a diffraction pattern completely across the field and your line does not line up with the other diffraction patters that you see in the field. If the vanes in your spider don't form a line through the secondary because they are pulled out alignment in the other direction, you'll get split lines showing two diffraction patterns on each side of the star at very slightly different angles and I don't see that in your data. Orion is a region of the sky pack with satellites. So go double check your data for satellite trails. John |
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John Hayes: Thanks John Yeah I'm pretty sure that is not something with my stacked image. The images I've uploaded are single frames. And depending on the filters are more or less present in the image. I've printed a new spider for my ota. I'll try to install it tomorrow Regards!! |
