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Any Hope for Tak FS-102 Binoviewer?

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#1 ThomasWos

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Posted 02 February 2013 - 01:08 PM

I have a 2003 FS-102, (fixed dewshield).

Is there any binoviewer that will achieve focus
with this scope?

Thanks,

Tom

#2 tomcody

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Posted 02 February 2013 - 01:27 PM

On my FS102 ( fixed dewshield), I can reach focus with either a Maxbright/ Baader prism &1.25 corrector or my new Mark V / Baader mirror & 1.25 corrector no problem. For more in-focus with either, use a Feildstein #4 adapter ( 72mm to T- thread) instead of the 2" adapter on the scope.
Where you will have an issue is trying to fit in the Takahashi CAA, you don,'t need it with the 2" adapter and if you use the Feildstein #4 adapter, you can use a Baader quick release to allow the binos to rotate.
Rex

#3 ThomasWos

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Posted 02 February 2013 - 01:51 PM

Thanks Rex.

Do you mean a Maxbright binoviwer with:

- T2 90° Prism Diagonal(32mm Baader prism)

- Baader Glasspath Compensator 1.25X ?

I already have the dedicated FS-102 Baader 2' ClickLock if that's what you mean.

#4 tomcody

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Posted 02 February 2013 - 03:14 PM

The 2" Clicklock diagonal uses up too much in-focus (about 120mm - I think?). You only have 198mm total on that scope, minus 40mm for the Tak 2" adapter, (and about the same for the Clicklock 2" adapter, if that is what you are referring to ?), leaving you with about 158mm available in-focus. The Maxbright/Baader 32mm T2 Diagonal/ 1.25 GPC combo requires 131mm of in-focus (134mm if you use the Baader-Ziess diagonal). I suggest you go to Alpine Astro's web site and download the Maxbright bino manual in PDF. It has detailed charts of all the above combos of in-focus required.
Rex

#5 johnnyha

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Posted 02 February 2013 - 06:06 PM

It sounds like Thomas should be okay with the 1.25X glasspath and T2 prism diagonal with the Clicklock visual back.

Thomas, the Fieldstein adapter Rex is referring to is a visual back that is simply a male T2 connection, so you can remove the nosepiece from the diagonal and screw the diagonal directly onto the end of the drawtube. With this I imagine you could reach focus at 1X, assuming you want to maximize your widest field. But like Rex says you would need to add a quick changer to rotate the diagonal. You should be fine with the 1.25X glasspath and your existing setup though, and in fact if you are doing planetary/lunar viewing you probably might want a 1.7X (which is actually closer to 1.5X) or even the 2.6X glasspath. With the 1.25X, a pair of 10mm eyepieces will only give you 100X.

#6 ThomasWos

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Posted 02 February 2013 - 07:08 PM

Thanks Rex and Johnny for your replies.

I've got the MaxBright documentation and have also studied Alpine Astro's web pages.

Yes, I have the 2" Clicklock on the back of the scope. Nice to keep that for rotation.

Then the 1 1/4" T2 diagonal interface with the 2" Clicklock would have to be addressed.

I'm shooting for about 175X for planetary, so yes the 1.7 or 2.6 corrector should work.

Not sure about the implications of corrector value versus EP focal length.

Also not sure about prism versus mirror diagonal either.

As usual, lots of research on the forums should be in order!

Thanks Guys!

Tom

#7 johnnyha

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Posted 02 February 2013 - 07:41 PM

Then the 1 1/4" T2 diagonal interface with the 2" Clicklock would have to be addressed.

No problem there Tom, just make sure you get a 2" nosepiece for the 1.25" T2 diagonal.

As far as your magnifications, you don't want to get binoview pairs shorter than say 9 or 10mm fl, so a simple way to figure out your mags is to figure 10mm as your smallest ep. At 800mm fl a 10mm gives 80X, times 1.25 glasspath equals about 100X. A 1.7X glasspath would give you 138X but probably closer to 120X, as the 1.7 glasspath is closer to 1.5X. So you are looking at either getting 7mm eyepieces, or adding a barlow, or getting the 2.6X glasspath to achieve 170X+.

Another interesting alternative - If you have a 2X Powermate, you can remove the long body and screw the short barrel directly onto the Maxbrights for 2X. Add the 1.25X glasspath for 2.5X or the 1.5X glasspath for 3X. This is my favorite way to achieve high powers with the MkVs. For this though you would use a regular 2" mirror diagonal and not the T2 diagonal.

#8 Eddgie

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Posted 02 February 2013 - 09:12 PM

As mentioned, if you go to the Maxbright Standard or Baader Prism (Zeiss prism), you can get the 2" nose, and this is indeed preferable to the 1.25" nose. This is because the binoviewer creates a lot of torque if you have to tilt it to one side or the other and it is hard to keep in locked in place with a 1.25" nose.

The Maxbright/T2 is the shortest light path which allows you the chance of reaching focus a 1x. The Zeiss is slighly longer, and the mirror is slightly longer still.

If you get the 1.25" GPC and use the 2" (or 1.25") nose, if you need a bit more magnification, you can move the GPC between the front of the diagonal and the nose piece. This is not documented in the Alpine Astro document, but it gives about 1.5x when positioned there, and gives you about 10mm more backfocus.

Measure carefully and decide if you want 1x, and keep everything as short as possible, and maybe you can get there.

If you don't need 1x out of the binoviewer, then keeping the light path short is not as critical.

Good luck.

#9 ThomasWos

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Posted 02 February 2013 - 09:58 PM

Thanks Eddgie,

Actually I welcome the focal length increase using the glasspath correctors.

I find myself wanting about 175X to 200X without using really short EPs.

#10 johnnyha

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Posted 02 February 2013 - 10:42 PM

Honestly then you are a good candidate for the 2X Powermate. When you unscrew the body the 2x PM is actually low profile and has a T2 connection, so it screws onto the front of the Maxbright like a nosepiece. Then you don't need the T2 diagonal, you can use whatever 2" diagonal you are using now. With this configuration a 10mm eyepiece gives you 160X, and adding a 1.25" glasspath you get 200X. You'll have no problems reaching focus.

#11 Erik Bakker

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Posted 03 February 2013 - 04:37 AM

Hi Tom,

I use a TeleVue BinoVue with my FS102 NSV. With the built-in 2x corrector, it is almost parfocal with say a 22mm T4 Nagler, so you will be fine with your FS102. My favorite plnetary combo i the BinoVue with 2x corrector , TV 2x BIG barlow and 19mm Celestron Ultimas. Stunning views with 170x magnification. The closest currently available eyepieces would be the TV 19mm PO. You might even go with the TV 17.3mm Delos.






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