Odd Shaped Stars through 6" Refractor.

[mhudson]

Ladies and Gentlemen,

Could I please ask for some assistance.  I have recently replaced my set-up with a Paramount MyT and APM 152/1200 Refractor.  I finally managed to get good weather and got to take the gear out and start learning it last night.  It's a steep learning curve with the MyT, but I knew what I was getting into and I'm learning fast.

I was rather eager to take a couple of shots through the new (well second hand) scope - I've never owned a refractor of this size before and I've had it sat around for months while waiting on the mount to arrive.

So I hooked up my Canon DSLR and I was very disappointed with the result as you will see from the attached image.  It's only a 10 second mono image but you can obviously see "comet" shaped stars across the whole image field - not just corners as I would expect without a reducer.  I'm not an optician so really need some help to try to understand what is going on.  It was late by the time I took this and with work the next day I had to pack up.  In hindsight I should have taken some in and out of focus images, but I didn't.  I did try with a diagonal and eyepiece with the same result.

I'm hoping this is not a serious optical problem or collimation.  I did wonder afterwards if  "maybe" I had the dewshield locking thumbscrew too tight and it caused a slight deformation of the optics?

Any help or advice will be much appreciated.

Kind Regards

Mark

[vlaiv]

Not an expert, but it looks like the scope needs collimation.

Coma like that can be caused by one of the lenses being slightly tilted (I guess its a doublet). Check if lens cell can be adjusted.

Do inspect in/out focus images at eyepiece, with this level of coma you should have no trouble spotting miscollimation even if you've never done it before.

[DirkSteele]

Is this an APM LZOS triplet 152?  This unfortunately reminds me a little of an LZOS 105 that Mr Rohr in Germany gave some TLC to.  The link to that (which was corrected) is below.  In that one the scope had been left in an observatory and some severe cold had compromised the scope.  The primary issue was astigmatism (not seen in yours) which was corrected by loosening a front retaining ring, but there was also some coma, which was fixed by centering the lens elements and hammering the lens spacers (With a rubber hammer).  You can put the article through Google translate.

 

http://r2.astro-foren.com/index.php/de/9-beitraege/01-aeltere-berichte-auf-rohr-aiax-de-alles-ueber-apos/118-a054-tmb-sanierung-nr-105-lzos-nr-105-651