Help diagnosing these stars

[R1k]

Hi guys, having persistent issues with my TS optics 80mm triplet. Started when I received this (used) scope a few months back - pinched optics which have now been Un-pinched. Had a few nights where stars were looking reasonably good again.

 

went out last night and had very odd looking stars. Optics not pinched, no play in imaging train, no focuser tilt, persisted when field flattener taken out of the train and no dew whatsoever. 
 

Rotated the OTA and the shapes persisted in the current direction they’re in below.

Anyone seen this before (easier to see when zoomed)

[R1k]

Could it be due to sudden temperature change? I took the scope outside in the freezing temperatures directly from a warm room?.. 

Edited January 7, 2021 by R1k

[KP82]

39 minutes ago, R1k said:

Could it be due to sudden temperature change? I took the scope outside in the freezing temperatures directly from a warm room?.. 

Could be tube current.

But if the orientation of this weird star shape does not change with the rotation of the OTA after the scope has acclimatised to the outdoor temperature, this could suggest a mis-collimation in the lens.

[jonathan]

I'd go with the collimation or dew thing.  I had a very similar looking effect from my DSLR and zoom lens, couldn't find the cause but I can only think that it had to be either collimation (which I'm never going to be able to sort out) or some fine dew that I couldn't even see (maybe on the CCD?)  It was a bitterly cold night when I did mine, perhaps it could also just be down to the electrical characteristics of the camera sensor not being able to function correctly at that temperature with bright point light sources?

[Waldemar]

That is definitely no dew... Coma, probably caused by mis-collimation.
camera sensors do neither show such effects by temperature issues.

What did you do for 'unpinching' the optics?
To me it looks as if the triplet lens system is being taking out of it's housing and been put back in wrong...
Meaning not using the same positions of the lenses as in the original settings from the factory.

[Captain Scarlet]

Looking at the orientations of the coma (long axis of coma pointing towards above the top-centre of the image) it looks as if there will be a coma-free point somewhat above the top of the image. That suggests to me as well, miscollimation.

Magnus

[R1k]

15 minutes ago, Waldemar said:

That is definitely no dew... Coma, probably caused by mis-collimation.
camera sensors do neither show such effects by temperature issues.

What did you do for 'unpinching' the optics?
To me it looks as if the triplet lens system is being taking out of it's housing and been put back in wrong...
Meaning not using the same positions of the lenses as in the original settings from the factory.

Thanks for the response. I loosened the retaining ring on the lens cell (which was EXTREMELY tight, jiggled it around a little and then finger tightened it. I’ve not adjusted anything else at all.

Below is an image of the whilst the optics were pinched a few weeks back 

 

Edited January 7, 2021 by R1k

[R1k]

And here is an image just from 3rd January where it was looking quite a bit better. I hadn’t done anything since then (to my knowledge at least) to cause the optics to become mis-collimated.

Edited January 7, 2021 by R1k

[R1k]

And single frame from 3rd jan where things weren’t looking so bad. I’m really at a loss as to what’s gone wrong since 😔

[Waldemar]

You say the optics seemed to be pinched and it had a really bad coma, maybe the first owner jacked with it and put things back together wrong...
In the factory those triplets are put together on an optical bench and a few rotational degrees off may cause bad effects.
if I where you I would ask FLO if they can service your scope and realign the lenses

[TerryMcK]

I've seen that before with one of my scopes. It turned out that the backfocus was a tad out and during the colder weather it was more noticeable. The scope itself was alright in my case.

Have you tried altering the shimming of your camera.

[R1k]

15 minutes ago, TerryMcK said:

I've seen that before with one of my scopes. It turned out that the backfocus was a tad out and during the colder weather it was more noticeable. The scope itself was alright in my case.

Have you tried altering the shimming of your camera.

Thanks Terry - yes with the field flattener I tried 55mm and 62mm (7mm spacer) backfocus - same issue both ways.

 

issue also persisted without any flattener at all.

 

edit - using a modded Canon 800d (sensor set back 55mm)

Edited January 7, 2021 by R1k

[TerryMcK]

Ok at least that has got that out of the equation. That does seem to narrow it down to the triplet as others have said and get a realignment. I always steer clear of adjusting the optics and leave that to the pros.

[R1k]

Just to update - thanks to all who helped. Scope has been sent to ES Reid in Cambridge today.