Help! I think there's astimatism in my new FSQ

[jackrussell0232]

Gents, Ladies, please don't laugh (you can gloat of course), but I'm getting acquainted with a new FSQ106ED.

At the same time, I'm testing a GM1000HPS (still...)  

Odd star shapes have occasionally come with the territory so far with this mount, but I had some very strange results with the 'new Q'.

The long and short of this, is that I've discovered that slightly out of focus stars are elongated in one direction, and this direction swings thro 90 degrees when I go from intra to extra focal positions.  The fully defocused star images look round enough, but this is really disappointing.

I'm just hoping someone can reassure me that this is not normal, and that I should get it replaced rather than just refunded.

I know Ian K will look after me, his service is always excellent, just want to make sure it's not just me that thinks this isn't good enough.

Any advice welcome,

Jack

[StarryEyed]

Jack.

The best advice is talk to Ian. If any body can give you an authoritive opinion it will be him.

Other than that dont panic, it will get sorted out.

Regards

[dweller25]

Jack,

Make sure the scope id FULLY cooled down when making the assesment.

[davew]

Jack,

Don't rely on a stranger's opinion on this kind of money ! Go straight to Ian King.

Dave.

[Velvet]

this is my set up too, i have no problems that you describe.  All works a treat.  Definitely speak to Ian and send him images, he will

sort it for you

Velvet

[steppenwolf]

Your description of the elongation rotating 90 degrees is certainly classic astigmatism. Ian K is a great, supportive dealer so I'd speak to him for his opinion. Sadly, just because it is a Takahashi does not mean that it must be faultless.

[jackrussell0232]

Thanks for the feedback guys.  

Although I've seen a few artifacts on different scopes due to cooling and tube currents, I've never seen astigmatism.  But I know from my baby Q that the petzval design does some funny things, (like making incorrect reducer to ccd spacing look like field rotation rather than field curvature).

It being June and all, I typically only get the roof off at 2230, and the scope has probably reached 25 degrees during the afternoon, but it had had 3 hours to cool by this point (0130),  and the temp sensor on the focuser was reading 15C when the temp outside was 13C, so I don't believe this should be thermal.  Can the elements really take >3hrs to cool?

But I was kind of hoping someone would come back and say, "I had this while the OTA was cooling, but once at equilibrium it was perfect".  Or that someone would say "yes I had a tak that did this. I returned it and the replacement was perfect".

It really won't do though.  The star elongates immediately that perfect focus is lost and grows to an oval with a major diameter around double its focussed size before it starts to go round again.  I'm not sure if this is why when I have the bahtinov mask on it and achieve perfect focus, the lines generated by the mask are slightly curved/wiggly, not straight............  They don't wiggle though, which is why I don't think it's tube currents.

Looks like I will be testing Ian's patience again.

Thanks for the help.

Jack

[harry page]

Hi

Just be sure its not the eye piece , rotate the eyepiece if the astigmatism does not move its the scope , probably pinched optics   

Harry

[jackrussell0232]

What's an 'eyepiece'?  

Sorry, that would be a Frejval question, but couldn't resist.

Having said that, this snag was detected with a ccd - I haven't formally star tested it with an eyepiece yet, as I bought it for imaging only really.

Seriously though, thanks Harry.  You make me wonder if the tube rings supplied are too tight.  I loosened the top halves last night to see if it made any difference and the scope didn't slip when I relaxed my grip on the heavy end, so the bottom sections must have been squeezing it a little?

Thoughts?  They are a new tube ring type supplied by Ian, made in the UK, not the traditional parallax jobbies.

[harry page]

Hi

Possible I suppose , but unlikely

If its pinched in the warm weather , no hope in the cold    or just could just be poor optics

If you can't sort it Ian will be of help

Harry

[perfrej]

Haha! Yes, That is a Frejvall question. I actually own four eyepieces deposited at Olly's. Maybe I should try one of them

As for your FSQ, start with elimination of focuser problems. I find the Tak focusera somewhat lacking in stability and you may want to tighten it a bit and give it a shot. How much does it wiggle if you apply some force to the business end of it?

/per

[jackrussell0232]

Per, I thought that comment would make you smile.

I did look at the focuser and see if it had any play, but it seemed really solid.  I tried to adjust the 4 screws, but couldn't set them any tighter without almost locking the drawtube solid.  With the spacers I have fitted, the focuser is only extended about 1-2mm. 

I think the GM1000 model was probably ok, with decent dual-tracking, because the 10 minute subs looked much the same as 10 second ones - but they all had strange shaped stars!

I'm hoping to have solved my problems by the time the dark nights return.

Ian King has said he will arrange a replacement, but I'm working away from home at the moment, so this won't be for a couple of weeks.  I'll let you know how I get on.

Jack

[ollypenrice]

I does sound like astigmatism doesn't it. Ach, the shame of it!! I haven't seen this on cool down on any of the FSQs I've used here for imaging. (2x106N and 3xFSQ85.) I've seen focus drift but not distortion associated with it. Houston, we have a problem.

Olly