Takahashi FC100-DL help...

[Mr Jones]

Hi folks. I am picking up a used Tak FC100-DL in the next week, but need some advice.

It no longer has the extension tube kit that originally came as part of the package. And currently has a Baader M72-68 adapter on the draw tube, followed by a Baader 2" click lock.

I am currently limited to my Tak 1.25 prism, Tak orthos (9, 12, 18, 25) and x2 barlow).

As the barlow is designed for use pre diagonal, I'll need a Baader reducer in the current 2" click lock.

But what I can't get my head around, is if I'll require a Baader m68 extension tube to enable me to reach focus.

I know I could wait until its here to test and see what is required, but I'd really like to have everything here and ready to go when it arrives.

I believe the M68 tubes come in 10mm, 20, 40, 60, 80 and 100mm options.

Any ideas what I require?

[John]

Hi,

I have a Tak FC100-DL. I don't find that need the original long extension tube. I use the stock Tak 2 inch visual back plus the 1.25 inch Tak step down adapter into a Baader T2 Zeiss Prism diagonal (which may well have a similar light path length to the Tak prism). I find this arrangement allows all my eyepieces (Delos, Pentax XW's and a Nagler zoom) to come to focus with plenty of drawtube travel in hand both directions:

If the Baader click-lock and M72-68 adapter has a similar optical length to the Tak 2 inch visual back then you should be OK to use the Tak 1.25" step down adapter if you have it or alternatively something like a Tele Vue "Hi Hat" 1.25" adapter.

 

[Mr Jones]

Thanks, John.

It doesn't have the Tak step-down or other original parts. Just the Baader M72/68 ring and 2" click lock.

Looking at the length of yours up to the prism, I'm thinking a 20mm extension...

https://www.firstlightoptics.com/adapters/baader-m68-extension-tubes-zeiss.html

...plus reducer...

https://www.firstlightoptics.com/adapters/baader-clicklock-2-125-adapter-2956214.html

Do you think that should work?

[John]

I've done some measurements of my rig. The 2 inch visual back, right back to the end of the silver drawtube (red line below), has an optical length of 55mm. The 1.25 inch step down and adapter (green line below) has an optical length of 45mm. I use a 15mm T2 extension (blue line) on the 1.25 inch twist lock on the top of the diagonal prism to ensure my eyepiece barrels clear the prism face as well. Hope that helps a bit more.

 

 

[Mr Jones]

That's amazing, thanks!

With all that in mind I'll need the 40mm extension.

Cheers. I owe you a beer... if they still sell beer after all this covid business is done.

[jock1958]

I have an FC-100DL as well and my arrangement is similar to John's only difference is I added a TS 35mm extension tube for all my 1.25" eyepieces to achieve focus (Note: I don't have the 15mm T2 extension on my diagonal that John mentions)  Picture below with my 1.25" prism diagonal  

 

Edited January 10, 2021 by jock1958

[Mr Jones]

Thanks, Jock. Orderded the parts I need now. 😉

Edited January 10, 2021 by Mr Jones