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Orion 8inch f/3.9 secondary question

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#1 Cyntrifical

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Posted 13 October 2017 - 04:04 AM

Ok, so I made a mistake one night when trying to collimate my secondary and sort of put a slight bend in the spider vanes of my secondary. It isn’t majorly bent or anything but it is slightly noticeable. Is this something to be concerned about? Do I need to get new vanes or will a slght bend be unnoticeable in the diffraction spikes in images? I am going to try and flatten them some more in the next week as Orion is sending me a replacement secondary holder and 2mm allen screws as the originals were stripped upon trying to adjust it. This time around after changing out the holder I’m not using the stock screws. Ordered a set of Bob’s Knobs (CNsec30) 30mm secondary knobs so in the field I no longer have to fool with allen wrenches. Lastly, Imm saving to order some better collimation tools as I’ve been hsing a cheap svbony 1.25” laser collimator and an Astromania 1.25” cheshire sighttube combo through a 1.25” to 2” adapter which hasn’t provided good results. Currently looking at ordering the following tools per the advice of Martin at First Light Optics:
1) Ho-Tech Laser Collimator 2” (the one which uses a twist adapter to fit snug and centered in the drawtube)
2)CatsEye Infinity XL Autocollimator 2”
3)CatsEye XLS Teletube 2”

Would these be all I would need for A)Precise collimation of both the primary and secondary optics of a fast newtonian and B)Quick and simple touch up collimation of the primary while in the field?

Sorry for all the questions in one thread but I figured it would be better than making separate threads for each question. If you could just answer each question preceded by #1, #2, etc.

Thanks guys!

#2 Cyntrifical

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Posted 13 October 2017 - 04:10 AM

Here’s a photo of my secondary vanes

Attached Thumbnails

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#3 happylimpet

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Posted 13 October 2017 - 04:10 AM

Most of your questions arent numbered, but I would say that if the spider bend is visible, it will be visible in your diffraction spikes. Whether that bothers you is another thing - my diffrcation spikes are a mess, frankly, but I dont care.


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#4 sixela

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Posted 13 October 2017 - 06:48 AM

The thing I see is that the vanes do not form two parallel pairs (they need not be in each other's extension, but if you just want four spikes they do need to be pairwise parallel). I'd tighten the right vane somewhat, and try to wiggle the exact point of contact of the screws holding them to make it better (inserting washers between the knurled cap nuts pulling on the vanes and the tube will also help).



#5 Eddgie

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Posted 13 October 2017 - 08:08 AM

The thing I see is that the vanes do not form two parallel pairs (they need not be in each other's extension, but if you just want four spikes they do need to be pairwise parallel). I'd tighten the right vane somewhat, and try to wiggle the exact point of contact of the screws holding them to make it better (inserting washers between the knurled cap nuts pulling on the vanes and the tube will also help).

Yes, this is what I see too.  The vanes should be in perfect alignment all the way across.

 

What has happened is that the secondary holder itself has been over-rotated. Did you bend it in an attempt to get the secondary mirror to appear round?

 

I don't think you need to replace it.  I think you can re-form it if you are careful.   I think that you should go back to basics and get a strait edge, loosen the vanes a bit, then try putting pressure in the opposite direction to try to get the vanes to line up in straight lines so that they would line up with the yellow lines in the picture.  These are just like a spring steel, so reforming them should be easy enough. 

 

Vanes 2.jpg

 

Measure the distance from the vanes to the center of the secondary holder when you tighten and get the secondary holder centered using the screws on the ends of the vanes.  While it is loose, you can try to re-form any distortion you see.

 

Then recollimate.


Edited by Eddgie, 13 October 2017 - 08:15 AM.


#6 Eddgie

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Posted 13 October 2017 - 08:26 AM

And if the little tension screws are too loose, try tightening them to see if the secondary holder straightens some.  It appears that the vanes have bent at the roots (like a swirl) on the secondary holder perhaps by over-torquing the screws or something?    If you apply pressure in the opposite direction, you might be able to get the swirl out. 

 

To form them just press on either side with your thumb as necessary to get them free of any twist. 

 

Of course from a picture it is always hard to tell, but the vanes should look like the yellow lines and these appear to have kind of a swirl to them. 



#7 Jason D

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Posted 13 October 2017 - 12:49 PM

To OP, what is the size of your secondary mirror? I can only see a small percentage of your primary mirror. I do realize it could be an optical illusion due to the position of the camera and I also understand you have a fast scope. Still, I am interested to know the size of your secondary mirror.

Jason


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#8 thompeters65

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Posted 14 October 2017 - 06:39 AM

I have the same ‘scope. All the comments on the vanes pretty much cover my comments on the twist.

As far as the collimator I use the Ho-Tech Laser Collimator 2”. I find it quick and easy to use. Because I don’t move my ‘scope far I use it in my backyard just to check before imaging. It comes with a great case and shape cut foam padding which can easily transported.

#9 calypsob

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Posted 30 October 2017 - 09:32 AM

I think the spider is toast for imaging honestly, unless you can make a jig to heat it up and straighten the veins, your diffraction spikes will not be symmetrical. Luckily a replacement is not terribly expensive https://www.ebay.com...BAAAOxysstSVLx~  and probably a bit more sturdy that the metal one.  

 

As for collimation, I think you will be better off using your camera to collimate.  The tools you have should be fine for a good initial collimation.  Are you using a coma corrector yet? 


Edited by calypsob, 30 October 2017 - 09:34 AM.



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