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Another FSQ-106 adapter & working distance puzzle...

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#1 leviathan

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Posted 02 December 2019 - 12:58 PM

I know for many, myself included, FSQ-106 charts are a bit complicated to say the least. Now if we add 645 reducer here things get even worse.

So I've got aforementioned scope with large 0.72x reducer, apparently CCA-250 and KP86003 (?) adapters, as well as wide Canon t-mount. Am I using correct adapters ? (photos attached)

 

Now if I want to use it with SBIG STF-8300M CCD camera (16.5mm working distance to sensor) and ZWO 7x36mm filter wheel (20mm width) what else do I need ? According to this chart KP86003 adapter has M54x0.75 female thread on it ? And reducer's working distance from the end of it is 56.2mm ?

 

Also, 645 reducer threads directly into the rear lens group cell, not the focuser. While CCA-250 and all other adapters after it screws ON focuser. Now, how to maintain correct working distance in this case ? Especially when focus shifts over the night.

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#2 chadrian84

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Posted 03 December 2019 - 12:54 PM

First decide how you want to connect the EFW to the m54 female thread on part KP86003 (also called part 8A).  You could either get an m54 to m42 adapter and skip the Canon part, or it may be easier to use the Canon part and find a Canon to M42 adapter.  Then decide how you want to connect the EFW to the camera (m42 adapter to whatever the SBIG camera uses).  If necessary purchase appropriate extensions to get your sensor around 56.2mm from the tip of the KP86003; anywhere from about 45-65mm should allow enough room to find and stay in focus all night.

A benefit of the fsq design is that all you need to do is get in focus. Backfocus (aka metal back distance or what you’re calling working distance) can be ignored as long as you’re in focus.  The focuser will allow plenty of room for focus shift during the night.


Edited by chadrian84, 03 December 2019 - 05:15 PM.

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#3 leviathan

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Posted 03 December 2019 - 09:55 PM

Hi Chad. I saw your messages in other topics on similar questions when you bought your FSQ-106 and 645 reducer. Glad that you responded here !

How are things going since then ? Are you happy with your setup ?



#4 chadrian84

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Posted 04 December 2019 - 12:17 AM

Nadir,

The 645 reducer has worked ok.  I think I'd benefit from a tilt adjuster but I don't have enough backfocus to fit one.  Even with custom adapters to fully maximize backfocus I'm barely able to fit a camera, EFW, and OAG onto my Nitecrawler focuser.  With your setup you could probably fit a tilt adjuster if necessary (Gerd Neumann, Sidewinder, etc).

 

Good luck getting things set up.  If I can help let me know.


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#5 deepanshu29

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Posted 18 February 2020 - 05:06 PM

I got the 645 reducer for FSQ106EDX4. I am trying to install it with stock focuser. My imaging train has - 

 

FSQ106 Focuser --> Part 82 --> 645 Reducer (Part 18L) --> CAA 250 (Part 6A) --> Part 8A --> Part 33 --> Canon DSLR. 

 

I am noticing that the reducer has limited the focuser travel to barely 16mm.  Before installing reducer, focuser was able to travel about 30mm. Can you confirm that this is by design? 



#6 chadrian84

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Posted 18 February 2020 - 06:27 PM

You should have 56.2mm backfocus remaining after Park 8a.  See this chart.  I believe Part 33 is 12.3mm, so you'll have 52.9mm backfocus remaining from there.  Where you begin the focuser will reduce that 52.9mm by how far racked out the focuser is.  16mm of focuser travel is plenty.  I only had around +/- 3mm with my Nitecrawler and never had any trouble finding focus.



#7 deepanshu29

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Posted 18 February 2020 - 06:59 PM

I am not saying that 16mm travel is not enough. I just want to confirm that 645 Reducer limiting the focuser travel to 16mm is by design. I see that part 82 does not let 645 through completely, and this is what limiting the focuser to 16mm instead or native 30mm travel. 

 

My camera setup is currently at 56mm and it will plug directly into Part 8A. I should find focus easy roughly in middle of that 16mm travel. Hopefully will get to test it tonight. 



#8 chadrian84

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Posted 18 February 2020 - 07:46 PM

Ok, you're saying the reducer contacts Part 82 (KA36581) when the focuser is racked out just 16mm.  I can see how that would happen.  I never used the 645 reducer with the stock focuser but I suspect it's by design.  I'm surprised they wouldn't warn people about that or have some stopping mechanism though.


Edited by chadrian84, 18 February 2020 - 07:48 PM.


#9 deepanshu29

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Posted 18 February 2020 - 08:08 PM

Ok, you're saying the reducer contacts Part 82 (KA36581) when the focuser is racked out just 16mm.  I can see how that would happen.  I never used the 645 reducer with the stock focuser but I suspect it's by design.  I'm surprised they wouldn't warn people about that or have some stopping mechanism though.

Yeah, Part 82 hits the 645 reducer after focuser is drawn out by about 16mm. See the chart below. It just feels weird to me how it is designed. 

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#10 leviathan

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Posted 19 February 2020 - 05:04 AM

Your imaging train is correct. If you're not planning to add anything between DSLR and M54 thread of 8A then it's perfectly fine.


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#11 edif300

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Posted 19 February 2020 - 10:26 AM

Nothing weird on it. Seems it was designed upon requierements of maximun diameter for 60mm circle. At 16mm off, image is completelly out of focus (backward) and the focuser stops by reducer’s body with no optics damage. Someone interested in imaging big round donuts maybe? lol.gif


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#12 chadrian84

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Posted 19 February 2020 - 11:26 AM

How far racked out it reaches focus depends on what adapters/accessories you're using and how much backfocus they've taken up.  It could very well happen that someone would reach focus racked out greater than 16mm (if that were possible).


Edited by chadrian84, 19 February 2020 - 11:28 AM.

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#13 edif300

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Posted 19 February 2020 - 11:33 AM

How far racked out it reaches focus depends on what adapters/accessories you're using and how much backfocus they've taken up. It could very well happen that someone would reach focus racked out greater than 16mm (if that were possible).


No. No with reducer.

#14 edif300

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Posted 19 February 2020 - 11:36 AM

Pay attention to drawing into MBD: 73.5mm.

#15 chadrian84

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Posted 19 February 2020 - 11:41 AM

I've paid attention and I think you're confused.  There's 56.2mm backfocus left after Part 8a (KP86003).  Someone could rack out all ~30mm and have around 26.2mm remaining for their accessories.


Edited by chadrian84, 19 February 2020 - 11:46 AM.


#16 edif300

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Posted 19 February 2020 - 12:00 PM

I am not confused. Pay attention to drawing for using measures annoted there and respect it. No sense into looking useless problems.

#17 chadrian84

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Posted 19 February 2020 - 12:15 PM

What should I be "respecting" from the diagram that I'm not?  The reducer screws into the OTA and doesn't move when the focuser moves but all of the adapters move.  What are you disputing exactly?



#18 edif300

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Posted 19 February 2020 - 12:25 PM

Someone using 56.2mm MTB by tak adapters (DSLR) will rack out the focuser only few mm (7mm or so). Someone using 73.5mm MBD by custom made adapters will rack out the focuser same few mm (7mm or so). Follow the drawing and respet it. Reducer’s dimensions are by its spec.

Edited by edif300, 19 February 2020 - 12:25 PM.


#19 chadrian84

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Posted 19 February 2020 - 12:34 PM

If part 82 weren't blocked by the reducer when racked out 16mm, there are any number of imaging train combinations that could come to focus racked out greater than 16mm.  I'm sure others agree.  This conversation is getting nowhere so I won't continue.



#20 edif300

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Posted 19 February 2020 - 12:45 PM

Right. Following the drawing dimensions there is no need the looking for nonsense problems.

#21 deepanshu29

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Posted 19 February 2020 - 01:25 PM

Thanks for the confirmation guys. I felt it was weird because 

 

- I came from SW Esprit where the distance between flattener and sensor remain constant and focuser actually moves the flattener in/out. Same goes for reducer since reducer actually replaces flattener. So backfocus needed to be nailed down. FSQ design is different and since all optical elements are stationary, I can have minor flaw in my backfocus and focuser travel will take care of it. 

 

 - I am using Pegasus Astro Motor Focus Kit v2 with Ultimate Powerbox v2 to drive focuser. I always set max points limits in Pegasus driver so that motor shall not drive past that point. This system does not have stall detection and apply crazy amount of force past limits. Limits were consistent in case of Esprit regardless of flattener or reducer use. For FSQ, I will have to change the limits in driver when using with reducer. It is not a deal breaker but something that I will have to remember. I sure don't want to apply unnecessary force to reducer and damaging it. 

 

 

Rest, I understand that image train diagram very well. I will be using all Tak parts until Part 8A and my camera system will need to have roughly 56mm backfocus. 



#22 leviathan

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Posted 19 February 2020 - 01:31 PM

In case in the future you don't want to limit yourself with M54 thread of 8A for large sensors, you can always replace it with another adapter and get few extra mm.


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#23 edif300

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Posted 19 February 2020 - 01:54 PM

For FSQ, I will have to change the limits in driver when using with reducer. It is not a deal breaker but something that I will have to remember. I sure don't want to apply unnecessary force to reducer and damaging it. 

You can try to use adapters with goal to get focus point in the range 5-15mm at F5. With that way you don’t  need changing limits for using reducer. Could be? 


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#24 deepanshu29

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Posted 19 February 2020 - 02:03 PM

You can try to use adapters with goal to get focus point in the range 5-15mm at F5. With that way you don’t  need changing limits for using reducer. Could be? 

That's actually a good suggestion. I could eat away about 15mm travel in to adapters, then my focus point should be in roughly same place as with the 645 reducer. 


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