Misshapen stars - ?pinched optics

[R1k]

Hi guys, I have recently taken delivery of a used TS optics Photoline 80mm triplet which got its first light last night. It was shipped carefully packaged from Cyprus to the UK.

It quickly became apparent that my stars were misshapen, but in a consistent manner. I excluded the following problems - tilt, focuser misalignment, back spacing. 
 

A quick read revealed this was likely to be pinched optics, and indeed when I took the lens cell out, the retaining ring was incredibly tight. I have since loosened the ring and finger tightened it as per recommendations on other threads. Unfortunately I was unable to re-test as the clouds (and rain!) rolled in.

 

Would any of you experienced folk have a look at these images (one is just a tight crop of the other) to determine whether the misshapen stars appear to be consistent with the problem of pinched optics?

 

Thanks,

Rik

[Moonshed]

I don’t have the answer for you but others surely will, just wanted to say apart from the star shapes it’s a very nice picture of the Double Cluster in Perseus.

Edited December 13, 2020 by Moonshed

[wimvb]

That does look like pinched optics. Image a slightly defocused star, to see what the profile looks like.

if you google ”Suiter star test”, you will find more information on what diffraction patterns of pinched optics look like.

Edited December 17, 2020 by wimvb

[Adam J]

As above it's either pinched optics or trefoil, either way it needs to go back because there is not way that can be considered diffraction limited performance. 

Huum I have noted that this is a used scope....

Really the only thing you can do is send it back to the seller if he will accept it back or if he won't then send it to someone like wellenform.

http://www.wellenform.biz/ for adjustment. 

Not cheap. You could try releasing the pressure yourself if it is in fact pinching, 1/8th of a turn of each lens screw then test between with an artificial star. It can sometimes be the retaining ring but that is less common.  But if you go too far then it will make things worse and then you really will have to send it to them or another optical lab for bench testing and adjustment. 

If its ground into the glass they may be able to reduce the effect by rotating the elements but not fully remove it. 

Sorry to give you such bad news. Let's hope that what you tried worked. 

Adam

Edited December 17, 2020 by Adam J

[wimvb]

At each side of the triangles, there is a shadow which reminds me of mirror clips. If you look into the telescope from the front glass, can you see lens clips? 

I agree with Adam, this is definitely not as it should be.

[Adam J]

40 minutes ago, wimvb said:

At each side of the triangles, there is a shadow which reminds me of mirror clips. If you look into the telescope from the front glass, can you see lens clips? 

I agree with Adam, this is definitely not as it should be.

Lens clips will cause the shadows in the halo of a bright star...but they will not cause the star itself to be out of round shape. Mild pinching can have the same effect but this is not mild if I am honest. 

Edited December 17, 2020 by Adam J

[Merlin66]

I had very similar artifacts with an older s/h ED80.

By checking the orientation/alignment of the notches with the three collimating screws on the outer edge of the objective cell I found a 100% match.

Just "easing" the screws and leaving overnight to settle fixed the problem.

Touch wood, it hasn't come back in the last five years or so........

[R1k]

Hi all, loosening the retaining ring on the lens cell completely sorted this. I am still sending back to TS optics as I think it requires a little collimation (colour correction not as great as I expected!)

 

Thanks for all the help

Rik