William Optics ZS61 strange star "spikes"

[szychor]

Hello all , finally i got WO zenithstar 61 + dedicated flattener so i went to test it and there are strange "spikes" or  darker shadows around all brightest stars.What causes the and   how to get rid of them ?Its bit annoying .
Setup used for  test shot was ZS61+Flat61 connected to canon 800D via m48 adapter. 
Any help and ideas will be appreciated.

[Hallingskies]

I’m not familiar with the WO scopes but I had a similar problem with my old Vixen refractor.  In my case, the three black “notches” in really bright stars seemed to be caused by shadows of the edges of some clips that formed part of the primary lens assembly.  Look down the front of your scope and see if you can see anything like that.  I cut a thin circular gasket out of black card and sat it on the primary so that the clip edges couldn’t be seen.  Problem solved.  Apologies in advance if this is completely irrelevant to your situation.

[Merlin66]

Interestingly, on a s/h ED80 I bought it showed a similar thing - in my case four dark notches on each star....

There was no evidence of the usual spacers which could cause the problem.

Using an artificial star set-up I traced the notches to be aligned with the collimation screws on the outside circumference of the objective cell....

I gave each screw about 1/16 of a turn outwards....left the scope overnight and the next day the notches were gone and the collimation was still good.

If this is the problem, it could be it was aggravated by the colder conditions....

Hope this helps.

 

 

[CraigT82]

Could be the foil spacers between the objective lens elements I think

[Merlin66]

Yeah,

That's obviously the first thing to check......

[szychor]

Thanks for replies.  I unscrewed the dew cap and bingo there are 3 places with double screws in that shape . Which one do I have to unscrew upper or lower ones ? The lower screws are glued but upper ones aren't .

[Merlin66]

For simplicity I start with the ones which are not glued....they don't need much screwing out - as I said just a fraction of a turn - do the same to each screw.

Give the glass time to relax and test again. I could see the original notches easily visually with an artificial star, slightly out of focus; next day a perfect circular OOF image.

Softly, softly,.....

 

[szychor]

Thanks for help . Will try and post result.

[david_taurus83]

On a side note, I'm impressed by how little noise there is in your 800D image! Nice!

[Merlin66]

If you bought this telescope new from a dealer, then they should be doing this "repair" for you.........

 

[szychor]

Ok so far so good . I unscrewed lightly scerws and  nows it seems to be good . I made  a artificial star and it looks good , now need to test it outside at minus temps and see what happen .

[Merlin66]

Well done, looks promising...........

 

[Merlin66]

Any update????

 

[szychor]

As always when you buy new toy or it's starting to work as intended after tuning or tweaking the weather have to gone crazy  So currently i have 100% clouds  Maybe tommorow i have some hole in sky for 4 hours and will test  it.  Surely will post test results here if everything goes well  

[Adam J]

On 05/12/2018 at 22:51, szychor said:

Thanks for replies.  I unscrewed the dew cap and bingo there are 3 places with double screws in that shape . Which one do I have to unscrew upper or lower ones ? The lower screws are glued but upper ones aren't .

Ok not that I want to cause panic but those are the factory set lens alignment screws, if you had not already done it I would be screaming at you not to touch them. If you now find that your corner stars are odd shapes then altering those screws could be the cause. They glue them because they are never supposed to be moved by the user. 

[szychor]

I touched not glued only so it should be fine.

[Merlin66]

Any update on this issue??????

 

[szychor]

Still waiting for clear skies, but i think i wont be able to cjeck it on real star test for 1 week or longer because  the weather goes crazy ? But i made a artificial star from fiberoptic and after testing i think its ok  but this was tested in + temps so need to check it again after cooling it to minus temps. I found somewhere here on forum similar problem with some WO scopes and there was same pattern on stars and  it happened only when scope was exposed to minus temperatures (winter) and no problem at summer. SO it looks like the lens get pinched when exposed to minus temperatures. The only idea to avoid this is to use dew heater that will warm lens assembly .

[david_taurus83]

I have similar artefacts in my GT71 though not as profound as yours. Not enough to bother me yet to try and adjust.