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4" Wynne corrector distance from primary


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#1 lukepower

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Posted 28 March 2015 - 07:49 AM

Hi there,

 

I have been working these days to go (for the first time) to the Newton configuration of my scope. It all looks good, but once tested on the stars I found out that there was no way to get in focus. I would somehow need to go deeper with the corrector into the focuser. This would, however, result in the corrector getting into the light path.

Attached File  IMAG0319.jpg   118.39KB   4 downloads

Attached File  IMAG0320.jpg   147.03KB   2 downloads

Reducing the distance between secondary and primary is not an option, as it would prevent me from using the system in Cassegrain mode. 

I wonder if I could remove one of the outer rings which right now sits between focuser and the camera adapter (it is located on the outside of the corrector). Any ideas?

 

By the way, my DDM85-XL is now loaded, on the scope side, with about 115kg of weight (tube, camera and counterweights), and runs smoothly :)


Lukas Demetz
------------
www.skygemsobservatories.com
Astro Dolomites Observatory, Skygems Network
Santa Cristina Valgardena, Italy
20" Cassegrain-Newton on ASA DDM85XL


#2 lukepower

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Posted 28 March 2015 - 08:30 PM

Here a star test (if I can call it like that). Maybe somebody with a corrector can confirm the out-of-focus pattern of this image is okay, or if there is another error in there (dunno which one, though). The secondary is not perfectly aligned, but I guess it's not the biggest problem right now :P

 

Attached File  CCD Image 29.jpg   121.9KB   3 downloads


Lukas Demetz
------------
www.skygemsobservatories.com
Astro Dolomites Observatory, Skygems Network
Santa Cristina Valgardena, Italy
20" Cassegrain-Newton on ASA DDM85XL


#3 lukepower

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Posted 06 April 2015 - 06:55 AM

So here is the latest image I have been able to take:

Attached File  CCD Image 39.jpg   123.85KB   3 downloads

 

I don't really know where to look to get those stars round, all over the field the stars change shape: Frm squeezed to elongated to triangular :P Does anybody here have an idea?


Lukas Demetz
------------
www.skygemsobservatories.com
Astro Dolomites Observatory, Skygems Network
Santa Cristina Valgardena, Italy
20" Cassegrain-Newton on ASA DDM85XL


#4 prinzpaul

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Posted 16 April 2015 - 03:46 PM

Lukas,

 

IMHO your diagonal is not in shape.

Its tricky to get a large diagonal glued without tension. I've done it with Aquaria-silicone and have no problem with my 130mm diagonal

 

CS

Waldemar

www.schweifstern.de


ASA 8H, ASA DDM60, selfbuild 12" Newtonian with ASA OK3Z, AP 600 Mount, FLI 16803PL


#5 lukepower

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Posted 10 August 2015 - 07:35 AM

Hi Waldemar (and all others),

 

I have been fiddling on this collimation issue now for months. I got a new adapter from ASA which still won't get me to the right focus, so I rebuilt the imaging train, attaching the corrector to the CCD adapter with screws, hopefully eliminating any tilt in there.

 

I also re-aligned my spider with plenty of work (damnit!). Not having a closed tube sometimes matters, I had to work a long time to get it centered: I first of all used my Cassegrain focus with an inserted laser and checked the beam for being central in the tube. It was slightly off, so I fixed if getting it to +/- 0.5mm in the center of the tube. Then I aligned the spider to the laser - another two-men show with such a big scope. Done that, I added the secondary and checked for the beam getting in the dead center of the corrector.

 

Afterwards, I moved to the Newton focus, added the laser, and checked it getting beamed back through the center of the Cassegrain focus. Quite a task here, but it worked. So in theory, I should have my secondary perfectly aligned in respect to the back of the telescope. Having a Cassegrain main mirror (with a hole in the middle) certainly does NOT helps if you want to collimate a Newton... Anyway, this is the result without any work on the main mirror (which I would have to do under the stars, there is no other way):

Attached File  collinew.jpg   112.91KB   2 downloads

 

Any ideas and suggestions are welcome. This is definitively an improvement, and I really hope that the remaining coma and deformations are caused by the main mirror at this point...

 

 


Lukas Demetz
------------
www.skygemsobservatories.com
Astro Dolomites Observatory, Skygems Network
Santa Cristina Valgardena, Italy
20" Cassegrain-Newton on ASA DDM85XL





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