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Help With Adapters On Tak FS-60C

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#1 kklei940

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Posted 06 December 2021 - 12:20 PM

Hello, I'm having some trouble reaching focus with any of my 1.25" eyepieces in my "new to me" Tak FS-60C. I've tried everything from a 35mm Ultrascopic down to a 9mm Delite with no luck.

 

Would anyone with experience in piecing together these adapters know what I would need to gain more back focus with my 1.25" Televue Everbrite Diagonal? Here is how its currently set up where I still need more back focus. Any help would be greatly appreciated.

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#2 rollomonk

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Posted 06 December 2021 - 12:27 PM

Here's what works for virtually all the eyepieces I've tried:

 

fs60.jpg

 

You can find a system chart from Takahashi here: https://cdn.shopligh...tem-chart-1.pdf


Edited by rollomonk, 06 December 2021 - 01:20 PM.

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#3 Lagrange

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Posted 06 December 2021 - 01:24 PM

The Everbright has a longer optical path than some of the 1.25" prisms such as Tak's own and various models from Baader which could be a factor although my FS-60CB has a different arrangement of adaptors on the back which look a bit shorter than the ones you're using. Your FS-60C also has an 18mm longer tube after the objective than my FS-60CB which I presume translates to 18mm less back focus, so choice of adaptors and diagonal are probably more critical.

 

The adaptors I use are TKP2005 which threads onto the focuser tube, TKP00104 which acts as a coupler between the previous adaptor and the eyepiece holder, and TKP00101 1.25" ocular adaptor (as illustrated by the picture rollomonk posted). Another option would be to remove all the Tak adaptors and fit a Baader 2" ClickLock M56ix0,75 clamp (2956255) which has an optical length of just 30mm although it looks like you'd need a 2" to 1.25" reducers as well - Baader do an excellent ClickLock version but there are plenty of cheaper ones that would do the job.


Edited by Lagrange, 06 December 2021 - 01:25 PM.


#4 kklei940

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Posted 06 December 2021 - 01:48 PM

Here's what works for virtually all the eyepieces I've tried:

 

attachicon.giffs60.jpg

 

You can find a system chart from Takahashi here: https://cdn.shopligh...tem-chart-1.pdf

Thanks for the info, rollomonk. What sort of diagonals have you used with this configuration? It seems I've tried this combination and have not had any luck reaching focus.



#5 kklei940

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Posted 06 December 2021 - 01:51 PM

The Everbright has a longer optical path than some of the 1.25" prisms such as Tak's own and various models from Baader which could be a factor although my FS-60CB has a different arrangement of adaptors on the back which look a bit shorter than the ones you're using. Your FS-60C also has an 18mm longer tube after the objective than my FS-60CB which I presume translates to 18mm less back focus, so choice of adaptors and diagonal are probably more critical.

 

The adaptors I use are TKP2005 which threads onto the focuser tube, TKP00104 which acts as a coupler between the previous adaptor and the eyepiece holder, and TKP00101 1.25" ocular adaptor (as illustrated by the picture rollomonk posted). Another option would be to remove all the Tak adaptors and fit a Baader 2" ClickLock M56ix0,75 clamp (2956255) which has an optical length of just 30mm although it looks like you'd need a 2" to 1.25" reducers as well - Baader do an excellent ClickLock version but there are plenty of cheaper ones that would do the job.

Thank you, Lagrange. It appears I have what you are describing, except I have something sitting between TKP2005 and TKP00104 that isn't included in the diagram. But I would need this though I think, along with another extension since what I need is more back focus, correct?


Edited by kklei940, 06 December 2021 - 01:57 PM.


#6 plyscope

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Posted 06 December 2021 - 02:37 PM

For the FS60C you can also get a shorter threaded tube to give more back focus. This is just a matter of transferring the lens and focuser to a shorter tube. Collimation should not be affected.

 

https://www.firstlig...k_tsk06211.html


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#7 Lagrange

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Posted 06 December 2021 - 02:41 PM

Thank you, Lagrange. It appears I have what you are describing, except I have something sitting between TKP2005 and TKP00104 that isn't included in the diagram. But I would need this though I think, along with another extension since what I need is more back focus, correct?

You shouldn't need anything extra because it's likely that you need more in-focus rather than back focus.

 

When you rack the focuser out is it getting closer to being in focus or further away? If it's the latter and you can't reach focus with your setup then it's because of a lack of in-focus so you need to find a way to reduce the distance from the objective to the eyepiece.



#8 kklei940

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Posted 06 December 2021 - 03:22 PM

You shouldn't need anything extra because it's likely that you need more in-focus rather than back focus.

 

When you rack the focuser out is it getting closer to being in focus or further away? If it's the latter and you can't reach focus with your setup then it's because of a lack of in-focus so you need to find a way to reduce the distance from the objective to the eyepiece.

As I rack the focuser out it's getting closer to being in focus, but it seems I'm just a bit short. That's why I was thinking I needed another extension of some sort.

 

I didn't mention this originally but I did order TKP20001 from Land, Sky & Sea. It appears it's too big to screw into anything I have. If you look at the FC-60C system chart below it looks like TKP20001 will thread right onto my focuser, which it does. But I then have nothing that will thread onto TKP20001. I have TKP20005 (at least I assume that's what it is), and the chart says it should fit but it does not. 

 

So I'm wondering what the correct adapter would be coming off of TKP20001 to work with my setup.

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#9 rollomonk

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Posted 06 December 2021 - 04:56 PM

Thanks for the info, rollomonk. What sort of diagonals have you used with this configuration? It seems I've tried this combination and have not had any luck reaching focus.

Takahashi and Televue diagonals -- both have worked. Also, if you need more back focus, take a look at the Camera Angle Adjuster (CCA TKA21200) -- I got one of these in order to achieve focus with a DSLR -- see the bottom of the System Chart you posted. It doesn't work with my visual setup though, not enough in-focus.



#10 Lagrange

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Posted 07 December 2021 - 02:24 PM

As I rack the focuser out it's getting closer to being in focus, but it seems I'm just a bit short. That's why I was thinking I needed another extension of some sort.

 

I didn't mention this originally but I did order TKP20001 from Land, Sky & Sea. It appears it's too big to screw into anything I have. If you look at the FC-60C system chart below it looks like TKP20001 will thread right onto my focuser, which it does. But I then have nothing that will thread onto TKP20001. I have TKP20005 (at least I assume that's what it is), and the chart says it should fit but it does not. 

 

So I'm wondering what the correct adapter would be coming off of TKP20001 to work with my setup.

That's a surprise because I'd have thought you would easily reach focus with your mirror diagonal having a longer optical path than the prism I use as well as your FS-60C having a shorter metal back focus distance than my FS-60CB.

 

Mine came with a couple of other adapters that can be used to give more back focus. One is the coupling (TKP20006B) which threads onto the focuser tube, and there's a much longer extension (TKP20001) which connects to that, then it's the TKP20005 visual adapter , TKP00104 coupling, and finally the TKP00101 eyepiece adapter. Looking at your first picture I don't think you have TKP20005 in your setup.

 

One option would be to get a basic 1.25" extension tube and play around with that until you find out how much extra back focus you need. Once you know the amount you can always invest in the proper Tak adaptors but I'd be wary of spending the money now until you can be sure of what you already have and which parts you would need.



#11 kklei940

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Posted 07 December 2021 - 02:32 PM

That's a surprise because I'd have thought you would easily reach focus with your mirror diagonal having a longer optical path than the prism I use as well as your FS-60C having a shorter metal back focus distance than my FS-60CB.

 

Mine came with a couple of other adapters that can be used to give more back focus. One is the coupling (TKP20006B) which threads onto the focuser tube, and there's a much longer extension (TKP20001) which connects to that, then it's the TKP20005 visual adapter , TKP00104 coupling, and finally the TKP00101 eyepiece adapter. Looking at your first picture I don't think you have TKP20005 in your setup.

 

One option would be to get a basic 1.25" extension tube and play around with that until you find out how much extra back focus you need. Once you know the amount you can always invest in the proper Tak adaptors but I'd be wary of spending the money now until you can be sure of what you already have and which parts you would need.

Yes, I'm a little perplexed that I seem to need more back focus as well. The system chart says I should be good but I'm just a bit short. I wonder if it has anything to do with the TV Everbrite diagonal?

 

Anyway, I had the same thoughts on the 1.25" extension tube. I ordered one a couple hours ago from Agena. It was only $20 and should give me one inch more back focus. And like you said, if that one inch is enough I can figure out if I want to spend more on another Tak adapter for that inch instead of the extension tube.




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