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Imaging train threaded connections help

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#1 PeteM

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Posted 25 August 2019 - 08:47 AM

Hi all, I am setting up a new-to-me 383L+ w/EFW2 and discovered that I ran out of backfocus with my RC8,TCF-S, and ONAG. So I need to reduce the length somewhere. One spot was the camera/fw/2" nosepiece into the 2"holder I added to the ONAG. I can switch to a threaded connection there . But I was wondering how tight do you tighten them? This setup is starting to weigh a bit and what I thought was tracking issues the other night with just the camera alone was the train slowly rotating(unthreading?) Is by hand pretty tight the method others use or do you get "tools" out to make sure nothing will move ever?

 



#2 PirateMike

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Posted 25 August 2019 - 09:14 AM

No tools. If you tighten them really tight you may never get them apart again.

 

 

Miguel   8-)

 

.


Edited by PirateMike, 25 August 2019 - 09:14 AM.


#3 james7ca

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Posted 25 August 2019 - 09:27 AM

Don't use tools and don't make them really tight (firm hand only). If you are worried about them becoming unthreaded (or turning slightly) then wrap some good, stretchy electrical tape around the outside of the joint where the parts mate (after you've jointed them together).



#4 kathyastro

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Posted 25 August 2019 - 09:35 AM

Definitely use threaded connections rather than a nosepiece.  It is much more secure.

 

"By hand pretty tight" is the only way to tighten threads.  No tools.  If you over-tighten, you will never get them apart.  You can't use any lube in case you get some on the optics, so it is dry metal on dry metal.  You need to avoid having the parts seize together.

 

You should try to miimize the number of connections.  If you need multiple adapters to make up a specific back focus distance, it is worthwhile to get a custom adapter made.


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#5 PeteM

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Posted 25 August 2019 - 09:50 AM

Ok, so I will for sure not use any tools to tighten the threaded connections. Below is a picture of the image train and I have kept the connections to an absolute minimum I believe:

 

Back of 8" RC -> custom spacer (to expose primary mirror cell collimation screws) -> Tilt plate (focuser collimation) -> Optec TCF-S dovetail -> TCF-S -> ONAG -> spacer -> EFW2 ->383L+

 

The ONAG goes into the TCF-S via a 2" nosepiece and I do not see the ability to make that a threaded connection. Maybe someone knows how to make that happen with that focuser.

 

(I have some wire management to do too)

 

20190825_143923372_iOS.jpg



#6 pfile

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Posted 25 August 2019 - 10:21 AM

can confirm that stuck threads are a thing; have had to resort to strap wrenches to undo some threaded connections... also at the cost of my sanity as i worried that i'd never get everything apart...

 

rob



#7 PeteM

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Posted 25 August 2019 - 10:46 AM

I think part of my problem is with the ONAG causing the camera/fw to be offset from the centerline of the rear cell (and all the threaded components) creating extra torque. Hence thinking I need to tighten things up a bit more.



#8 kathyastro

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Posted 25 August 2019 - 11:01 AM

I think part of my problem is with the ONAG causing the camera/fw to be offset from the centerline of the rear cell (and all the threaded components) creating extra torque. Hence thinking I need to tighten things up a bit more.

I noticed that the imaging camera is off to the side, while the guide camera is in-line.  Is that the normal way to set up an ONAG?  With an OAG, you would do it the other way around: imaging camera straight through and the guide camera off to the side.



#9 PeteM

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Posted 25 August 2019 - 11:14 AM

I noticed that the imaging camera is off to the side, while the guide camera is in-line.  Is that the normal way to set up an ONAG?  With an OAG, you would do it the other way around: imaging camera straight through and the guide camera off to the side.

Yes that is correct, normal setup for the ONAG. There is a hot mirror that passed just IR wavelengths to the guide camera and reflects up to the imaging camera pretty much the normal wavelengths. This allows for using the main FOV for both cameras. Works great and I will do everything I can to use the ONAG instead of a OAG. But I do have one if I need it.



#10 kathyastro

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Posted 25 August 2019 - 11:56 AM

Yes that is correct, normal setup for the ONAG. There is a hot mirror that passed just IR wavelengths to the guide camera and reflects up to the imaging camera pretty much the normal wavelengths. This allows for using the main FOV for both cameras. Works great and I will do everything I can to use the ONAG instead of a OAG. But I do have one if I need it.

Thanks.  I had a rough idea how an ONAG worked, but I didn't know which wavelengths were transmitted and which reflected. 

 

I know that the 383L+ and EFW2 are heavy.  Would it do any good to rig a counterweight to prevent the weight from torquing the threads.



#11 Corsica

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Posted 05 September 2019 - 07:24 AM

Thanks.  I had a rough idea how an ONAG worked, but I didn't know which wavelengths were transmitted and which reflected. 

 

I know that the 383L+ and EFW2 are heavy.  Would it do any good to rig a counterweight to prevent the weight from torquing the threads.

If you consider an ONAG, I would suggest the ONAG SC since your sensor is a APS-C type.
The ONAG T2 (M42 x 0.75mm) thread and body can easily handle your camera and FW weight.
 




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