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Need some advice on collimating a 72ed


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5 minutes ago, WolfieGlos said:

Hi Lee,

I hope so! I feel like it's been a long time, a lot of testing and tweaking. Not helped by the late nights at the moment either haha.

I have a stock Canon EOS 77D. Correct, it is supposed to be 55mm for the Stellamira too and I started out with no spacers albeit with the standard 72ED push fit and a faulty t-ring which wobbled. These have since been replaced with a screwed fit and a Takahashi T-ring, which has no give in it at all.

On my first target (using the original push fit and faulty t-ring) with the 72ED, which was M51, it reports a 63% tilt in ASTAP and actually looking at the individual subs it is quite clear that the stars are very eggy, and to me ASTAP is reporting it correctly. As M51 was cropped quite a lot it's hard to see it in the final image (which I'm quite happy with!), but it is there, and without cropping it is very evident and from the star patterns suggests the backfocus needs increasing. That's why I have been adding spacers.

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Since I have been trying to collimate, I could actually try removing all spacers as well and see what that does.....thanks for that thought, will give it a shot and see what happens. But at the moment, my subs definitely show eggy stars, not so much of a problem if I'm cropping the image down like above, but a full framed target (i.e. Andromeda, NA, Veil nebulae, etc) will cause me big problems.

The below test image from Markarian's Chain shows it quite well with only the very extreme edges cropped off. Not a great image as it doesn't have many frames but taken as an example to see how bad it would be on a full framed shot. The individual subs report anywhere between 45-58% tilt, so similar to M51 above. When Andromeda rises into view again I intend to frame it diagonally from corner to corner to make it fit, but based on the below it won't be great. The bottom right corner is so bad the stars appear out of focus.... I would almost be forced to do a Mosaic.

Markarians Chain was the last one I took with no spacers, push fit and faulty T-ring, I got into contact with FLO afterwards who have been VERY helpful, and since those items were replaced (and spacers added) the tilt values and eggy stars have reduced but they are still evident.

I'm convinced it's in the focuser so will continue with it, I guess you're right, perseverance will get me there in the end.

Cheers,

Chris

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Hi Chris 

Yes it's most likely in the focuser side of things and it your dslr or connections. Once you get your laser collimator corrected it will be so much easier. 

I agree the late nights won't be helping with your issue but the evenings will start pulling in very soon 😊

FLO are extremely helpful and helped me in the past with tilt issues the collimation procedure and introducing a tilt adjuster to my zwo asi294mc pro sorted it much better. 

You will get there and the sense of achievement will he rewarded by your great images. You are getting there and finding the solution it does take small increments ad tweaks each time. 

Cheers 

Lee 

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  • 1 month later...
Posted (edited)

@WolfieGlos

Are you using a field flattener? because without one your stars will appear "eggy" around the edges of the frame regardless of what you do. Field rotation due to polar alignment error, focuser slop from the weight of attachments and tracking accuracy can all add fuel to the fire. I'd suggest taking some short exposures of stars and checking individual subs. Periodic errors in your mount will introduce minute star trailing that will affect the end result once you stack (and wind, orientation of the scope in the sky, weight of cables etc can all contribute). Apologies if I'm preaching to the choir :)

I found the cheshire quiet helpful to eyeball things as I went along and made my adjustments. As I mentioned previously, in my case I had to reset the orientation of the objective lens to get things right.  I'll still be tinkering away long after this post!

While software is useful for analysing what's going on, you should trust your own better judgement too, how happy are you with the pictures, can I get away with cropping 5% or more of the frame etc.

Edited by Sien
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  • 2 weeks later...

Hi Sien,

Yes, using a field flattener 🙂 

Agreed it's not best to rely on just the software, but I could see the eggy stars for myself. I do usually crop the images, but a full frame shot (i.e. M31 will fill my entire frame) will show up the problems.

It's been a while since we were posting above, but an update on what happened to me. So I was in constant contact with FLO support about this, and in the end to their credit they actually took the scope back under warranty to have it checked over. I now have it back, and whilst I haven't been informed exactly what was wrong, it did require adjustments and correcting, and is now working very well! 😄 

Whilst I have only just had it back and have used it so far for only 1 nights worth of imaging, my tilt value is very low (varies from 2%-8% across 150 subs....MUCH better than previous 25% and higher). But this new reported tilt value may also be off slightly due to backfocus, as I can see eggy stars in the far corners. I have a 5mm spacer added already, and it looks like it needs more as the streaks are inwards, so I will be continuing to alter this in the coming days with the predicted perfectly clear skies we have here (and typically a near full Moon......). But if the report from the ASTAP software is showing the below values with incorrect backfocus, (Siril gives a very similar reading too) then (in theory) improving the backfocus should make the corners better and lower the reported tilt. 

However, if this is the worst tilt that I get from now on, then I'm happy!

image.png.b0b06c931e4c7d4d153e5eb9b6b9d2c9.png 

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