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How do I achieve a "rigid"/non-slip camera train on my refractor?

Astrophotography Refractor
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9 replies to this topic

#1 cpl42

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Posted 02 July 2022 - 08:09 PM

Hi,

 

I own a William Optics FLT110. Now, the question I am asking has probably been covered elsewhere, and perhaps just providing me with appropriate links will suffice to answer it. However, it's just as likely that the useful knowledge is scattered across a whole slew of postings, and is not readily dug out - hence this posting.

 

Like all/nearly all refractors, the viewing end of the 'scope is just a clamp to hold diagonals and/or eyepieces. However, when it comes to holding a camera this method sucks! I suspect that many of us will confess to seeing/nearly seeing the camera slide out of the 'scop during a session. The camera side is relatively problem-free as adapters and tubes with threads can be employed. So, my main question is:

 

What do people do to get a solid, non-slip attachment of the camera+adapters to the end of the 'scope, specifically for my FLT110. I suspect that the clamp system and its housing have to go, but then what?

 

On a related, but different issue (and perhaps this needs a separate posting), using an automatic focuser suggests to me that the draw-tube lock needs to be loose. However, doesn't that mean that the draw-tube is likely to slip outwards once the OTA is pointing at high altitudes? How does one overcome this, or have I got something wrong, here?

 

Thanks in advance, and clear skies, Paul.



#2 CharLakeAstro

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Posted 02 July 2022 - 08:15 PM

The answer is threaded connections.

My William Optics GT71 > Flat6Aiii > WO rotator >  spacers > filter wheel > ASI183mm is threaded at every junction. The rear clamp is unthreaded from the refractor first, if ever I want to us it for visual, simply thread it back on. 


Edited by CharLakeAstro, 02 July 2022 - 08:18 PM.


#3 KTAZ

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Posted 02 July 2022 - 09:23 PM

100% threaded connections.



#4 RichA

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Posted 02 July 2022 - 09:44 PM

Unfortunately, telescope makers never saw the sense in making bayonet connections like camera makers did. 



#5 rkinnett

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Posted 02 July 2022 - 10:48 PM

I too prefer threaded connections, but not because of slip.  I haven't had any issues with heavy imaging trains falling out of 2" compression fittings, including the user error scenario (knock on wood).  Compression clamp connections are generally more prone to tilt and axial misalignment.

 

Regarding the focuser questions, it sounds like the focuser on your FLT110 is Crayford type with a friction plate and pressure knob to adjust holding strength.  This type is comfortable for visual observation, and it could work for basic astrophotography, but it's not ideal for use with heavy imaging trains and autofocusers for the exact reasons you outlined.  For AP you want a rack and pinion focuser which are much less prone to backdriving/slipping and also have an advantage in making focuser motion much more repeatable compared to the friction plate type.  Many scopes ship with Crayford style stock focusers, and many astrophotographers swap those out for Moonlite, FeatherTouch, etc R&P focusers.



#6 cpl42

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Posted 03 July 2022 - 03:08 AM

Wow! That was fast!

 

Thank you everyone for your very valuable inputs. It's going to take me some time to assess this information and decide what I should do.

 

Yes, the 'scope has a Crayford-style focuser (2-speed) - there is no rack-an-pinion. I have had a quick look at the FeatherTouch and Moonlite offerings and note that they, too, use compression fittings at the business end of their units. I didn't mention light-path droop (which is prone to altering as the 'scope changes orientation), and am very interested in eliminating this as much as possible. A screwed-only option would be very good. However, the compression fitting might be acceptable if the compression ring sits in a machined groove, minimizing movement. It would appear that all refractor manufacturers supply only this form of adapter.

 

I'll get back if I have any more questions, but I think I have enough to go on with at the moment.

 

My grateful thanks to you all.

 

Paul.



#7 Rasfahan

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Posted 03 July 2022 - 04:41 AM

Wow! That was fast!

 

Thank you everyone for your very valuable inputs. It's going to take me some time to assess this information and decide what I should do.

 

Yes, the 'scope has a Crayford-style focuser (2-speed) - there is no rack-an-pinion. I have had a quick look at the FeatherTouch and Moonlite offerings and note that they, too, use compression fittings at the business end of their units. I didn't mention light-path droop (which is prone to altering as the 'scope changes orientation), and am very interested in eliminating this as much as possible. A screwed-only option would be very good. However, the compression fitting might be acceptable if the compression ring sits in a machined groove, minimizing movement. It would appear that all refractor manufacturers supply only this form of adapter.

 

I'll get back if I have any more questions, but I think I have enough to go on with at the moment.

 

My grateful thanks to you all.

 

Paul.

All Moonlite and almost all FeatherTouch (except the 20XX crayfords) have threaded connections.  Many (most?) third-party R&P focusers also have threads on the end of the drawtube. The 2" clamps of these focusers are threaded to the drawtube. If availability of Moonlite or FT are a deterrent, I can recommend this one: 

https://www.teleskop...tersetzung.html

The Baader Diamond Steeltrack is quite a bit less expensive and also has a good reputation. Threads/clamps are attached via an S58 Dovetail system:

https://www.teleskop...or-Focuser.html



#8 cpl42

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Posted 03 July 2022 - 04:06 PM

Thanks for the alternative suggestions, Rasfahan. I've got my refractor with a friend at the moment who is looking into a problem I have with the focuser. Once I get it back, I'll see if the clamp unit can be unscrewed (it looks like that's the way it is attached) and if so, hopefully the thread is an M48, or similar. What I am leading up to is attaching an autofocuser to the draw-tube control. I'll try it out without resorting to a replacement if I can do it this way, otherwise, it's a replacement R&P draw-tube. The FLT110 has quite a long draw-tube and I would hate to replace it with something half the length. The TS-Optics 3,7" Deluxe looks comparable, though.

 

And, I'm definitely pursuing the screwed light-train. The only issue I have with this is after nipping up each component, the camera might be in an awkward position. The FLT110 has a rotating draw-tube assembly and this might be adequate, but are there alternatives that I can put between the drawtube and the camera? (This is only an interest question, it's not important.)

 

Clear skies, Paul.



#9 CharLakeAstro

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Posted 03 July 2022 - 09:50 PM

Recommend you also add a rotator if going to a threaded solution, to allow target framing.



#10 cpl42

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Posted 03 July 2022 - 10:42 PM

A good suggestion, CharLakeAstro. I'll look into it - back focus might be starting to be an issue for me.

 

Paul.




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