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Takahashi FC100DC & unbarlowed binoviewer


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The Takahashi FC100DC has only one drawback. It's focuser has limited inward travel! This can be problematic if the observer wants to use a 2" diagonal with 1.25" eyepieces, as with some eyepieces there isn't enough inward travel to attain focus. The same applies to the use of bino viewing without the use of a Barlow. All isn't lost however as the DC can be adapted without compromising the light cone from the objective.

Removing the green spacer tube which is situated between the main tube and the focuser, and then screwing the focuser body directly to the main tube allows plenty of inward travel. 

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Using the two black Tak extension tubes that come as standard with the DC allows the scope to reach focus with a 1.25" diagonal and 1.25" eyepieces.

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Screwing on a 2" back to the DC focuser and using a low profile 2" to 1.25" adapter allows plenty of inward travel for a binoviewer, without the use of Barlow lens.

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The advantage would be that short focal length eyepieces could be used for high power binoviewer observing, or low power viewing with longer fl eyepieces, though the latter may be of limited use in a 100mm scope, and vignetting may be a problem! Also, the scope becomes shorter to transport when the extension tubes are removed.

So, from this 

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to this

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It's up to you! :happy11:

Edited by mikeDnight
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Nice pics Mike. I've been installing a replacement feathertouch focuser on my FC100DF this afternoon. The first feathertouch had a bit of play in the fine focuser but replacement one is great. 

As per the previous thread there is loads of in focus with the feathertouch to the extent that I need to put a 2 inch extension tube in for my 2 inch diagonal. What struck me this afternoon though was how light the feathertouch focuser was in comparison to the Tak DF focuser - very material difference. I think the DC focuser is also a lot lighter. It does make the FC100 into a lovely lightweight 4 inch.

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Achieving focus with binoviewers is hard enough for me. Without a Barlow or PowerMate is the stuff of dreams!

But I'm attracted to the idea of binoviewing and will keep on experimenting for now. Part of the fun, innit? ???

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Thanks Mike - and Stu for the original thread. Although I removed the entire focuser unit from my FC for aircraft travel this summer, I didn't know that the spacer section could be detached on its own. Really useful as I'm using binoviewers more often

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  • 2 years later...
On 06/09/2017 at 18:45, mikeDnight said:

Screwing on a 2" back to the DC focuser and using a low profile 2" to 1.25" adapter allows plenty of inward travel for a binoviewer, without the use of Barlow lens.

20170906_170545.thumb.jpg.5ab827c21d32269078608925e3771ac2.jpg

The advantage would be that short focal length eyepieces could be used for high power binoviewer observing, or low power viewing with longer fl eyepieces, though the latter may be of limited use in a 100mm scope, and vignetting may be a problem! Also, the scope becomes shorter to transport when the extension tubes are removed.


Mike, where can I get this low profile 2" to 1.25" adapter?

Thank you!

Edited by Sergey
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Mine was quite tight when I initially tried unscrewing the spacer, but with a bit of determination it unscrewed ok. I didn't use any kind of tool for unscrewing, just a strong grip. Obviously you dont want to put your scope in any danger. 

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