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Help. Collimation or tilt?


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Back in 2016 I bought one of these star 71 telescopes.

When I used to image with an atik 383L I would get slightly weird star shapes and always assumed it was to do with tilt, but I could never get my stars quite right. so I decided to just live with it.

I recently got a qhy183C and my stars got a lot worse. I can only assume they appear worse due to the smaller sensor, or maybe there was something wrong with my camera. After my recent purchase, a William optics flt98, I can finally rule out the camera as this scope produces lovely, round stars. This raised my curiosity of the star 71 again so I purchased a hubble 5 star artificial star to try and test the collimation. But I'm not 100% sure how to read the results, so I'm asking the wealth of knowledge that is SGL.

Below is an image I took of m106 which shows the weird star shapes. Below that is an image I've just taken with my artificial star.

I'd be extremely grateful if anyone can analyse these images and give me some advice on if it is the collimation or tilt that is causing the weird star shapes.

m106 14 sub test.jpg

artificial star test.JPG

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Can you do a picture of a star field, then rotate the camera 90°, take another, then again, and then again?

Also, pictures with the artificial star, focused, with the image in each corner and at the middle of each edge, and the same positions about 1/3 of the distance closer to the centre of the frame.

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I'm confused. You bought from a dealer with full UK warranty (2 years?), it was checked by Es Reid and passed off 100% but you've always suffered from the issue? I'm not meaning to sound condescending but did you not highlight this with FLO? I'd be fuming if I spent that on a scope and got those results! If it is focuser tilt is that something the customer is expected to deal with? I have a GT71 so very similar to the Star71 but surely there isn't that much play in the 2.5" R&P focuser to cause those shapes?

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25 minutes ago, david_taurus83 said:

Star71 but surely there isn't that much play in the 2.5" R&P focuser to cause those shapes?

I have an original Star 71 and the focuser is not brilliant, lot's of flop in it, poor design with adjuster on one side that needs duplicating on the other side to enable better adjustment.

Couldn't get mine apart so have to set it up so the focuser is pretty much fully in just leaving enough travel to autofocus and inserted some adhesive PTFE tape to take up the play.

Dave

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Thanks for all your thoughts. It seems the consensus is focuser tilt so I downloaded the trial of ccd inspector and that says a tilt of 30% on the left. Looks like I'll have to do some research on how to fix it.

I received the stock focuser along with a moonlite focuser when I bought my flt98. Would I be able to swap the star 71 focuser with the stock flt98 focuser?

6 hours ago, david_taurus83 said:

I'm confused. You bought from a dealer with full UK warranty (2 years?), it was checked by Es Reid and passed off 100% but you've always suffered from the issue? I'm not meaning to sound condescending but did you not highlight this with FLO? I'd be fuming if I spent that on a scope and got those results! If it is focuser tilt is that something the customer is expected to deal with? I have a GT71 so very similar to the Star71 but surely there isn't that much play in the 2.5" R&P focuser to cause those shapes?

I know it's stupid of me to ignore the problem. I thought it'd be an easy fix since the star 71 has tilt adjusters but never managed to get it right. I guess I was wrong. 

8 hours ago, Tim said:

Can you do a picture of a star field, then rotate the camera 90°, take another, then again, and then again?

Also, pictures with the artificial star, focused, with the image in each corner and at the middle of each edge, and the same positions about 1/3 of the distance closer to the centre of the frame.

I'll do it tonight and upload the results tomorrow. 

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I managed to do a few tests the past 2 nights and I'm now sure my problem is focuser tilt.

My first test was an out of focus Vega which shows collimation is fine (to my untrained eye)

Next was getting focus sorted then taking an image, rotate, and take another. After a few images it was time for bed so last night was cloudy so back to the artificial star.

After some playing around with the focuser I think I may have managed to remove most of the tilt problem, but bed time called. Ill continue testing once the clouds disappear.

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