Binoviewing with a Tak FS128

[F15Rules]

I've wanted to be able to binoview with my FS128 pretty much since I bought it over a year ago?.

I've used a binoviewer with a previous scope and for certain objects, chiefly lunar, planets and globular clusters, I found the views with my previous 5" F15 refractor to be amazing. But that scope had had it's tube shortened to accommodate binoviewing without the need for a barlow or OCS lens: I don't like having to use a barlow lens to get focus as the actual magnification you end up with when using a x2 barlow for instance always ends up giving more like x3 or x4 magnification of a given pair of eyepieces, with the consequent much smaller field of view and other problems associated with very high magnification.

Now, cutting down my FS128 tube seemed to me to be tantamount to sacrilege (Takahashi did actually offer a BV friendly FS128 version with a shorter tube, but mine is the longer tube version). So I wanted to see how, if at all, I might be able to get close to native focus without chopping the tube: I actually thought that the best I might achieve would be needing to use a 1.25x OCS from Baader, but thanks to some good advice from a fellow amateur on CN USA (who is also a member on SGL), and his wonderful generosity in actually gifting me several parts of the optical chain, I have been able to arrive at a solution whereby I can achieve perfect focus with my FS128 and using NO barlow lens at all - last night I had brief, but wonderful BV views of the moon and Jupiter at c 9pm, while it was still very light.

I thought it might be helpful to list how I have got to this point, and which parts were used: I realise that the FS128 is not a common scope, but it might be possible to use/acquire equivalent parts for different Taks and maybe for other scopes too.

Most of the parts listed are Baader parts: it does require use of a T2 system, which for me means a Baader Maxbright binoviewer: I don't know of any other make that uses the T2 system, but perhaps someone who reads this and does have any additional information on BVs which use, or can use T2 connections, could chime in here ??

I'm attaching some photos to show the parts "chain", and I hope these are helpful. I have also quoted the Baader parts reference number which may make it easier for you to source these if you are interested. I should say that my FS128, being an older scope, uses different threads to some newer Taks, but it may well be that you can find Baader equivalent adapters for these new Taks, and also maybe for Vixen apos and Skywatcher ED scopes as well - but I can't guarantee that.

Using BVs with native eyepieces is a wonderful experience. Last night I used a pair of Parks Gold 25mm Japan eyepieces which gave me c x42 in my 1040mm focal length FS128. Using this configuration I still had c 15mm or more of in-travel left - I will check this in-travel more precisely and add it in to this thread: I have so far only used the pair of 25mm eyepieces, but I have a pair of 10mms that I can also try - they are normally parfocal in cyclops mode, so I would expect them to work at the same in-focus distance as the 25mm pair.

 

Starting from the left hand side, the first component (M72/M68 adapter) threads into the Tak original focuser tube.

Next is the Ultra Short 2" Photo/Visual Clamp..

..Into which the T2 prism fits (The Baader T2 prism here is fitted with a 2" to T2 nosepiece.. The T2 nosepiece connects to the T2 thread on the front of the prism)..

The Parks Gold 25mm eyepieces just fit into the eyepiece holders and can be separately fine focused as required

1)   Above and Below photos, attached to scope focuser tube thread:   https://www.365astronomy.com/Baader-made-Takahashi-Adapter-M72-M68-Zeiss.html

2)  Now add this part: https://www.365astronomy.com/Baader-Ultrashort-2-eyepiece-clamp-with-M68-male-thread-Baa-9-2458196-32.html

Above shows 2" nosepiece being inserted into ultra short clamp, the T2 thread on the other end of the nosepiece threads into the Baader Prism front end

The Baader Maxbrights are attached to the T2 prism by T2 thread

The eyepieces can be used as normal with no barlow in my setup :-).

I must mention SGL (and CN) member Nicosy and thank him for suggesting some of the parts and how they might help me reach my goal of native eyepiece binoviewing  and very kindly and spontaneously donating some of the parts I needed-  a top guy!

I hope this is of interest and maybe of help to someone else?

Dave

[Stu]

Great stuff Dave, excellent news and very generous of the person who helped you out!

It looks like a very neat solution. I use a Baader Zeiss Mark IV binoviewer which has a flange on the bottom which can attach directly via T2 quick changers so allows a shortened light path too.

Looking forward to a first light report.

[F15Rules]

Thanks Stu.

I've currently got a problem with my right eye, and had 2 hours with an optician yesterday, so observing with my "normal " cyclops eye at the moment is impossible, as I am seeing lots of artifacts (floaters).. what with light nights, lots of cloud and work commitments, last night gave me an unexpected chance to try out this configuration - I first put it together almost 2 weeks ago, then went on holiday abroad for over a week etc etc..

I didn't want to post until I had tried it out to see how it worked: I honestly thought I might get close to sharp focus with no barlow, but still need a 1.6x barlow to get a sharp view. In fact, it was clear last night, and we had visitors round, so I suggested they might like a look at the moon briefly. So I put the bvs in with the 25mm eps, and they were gobsmacked at the view, while I was gobsmacked that I could get perfect focus with room to spare!

Sadly, my own bv view wasn't perfect due to my eye, but I could see well enough to see that the configuration above worked perfectly.

The optician said that the problem isn't serious, but it is due to advancing age and he said the viscous "liquid" inside my eye is becoming thinner, and that this allows "bits, or sediment" inside the eye to move about and form a milky like film which really affects the sharpness of my sight through that eye. My left eye seems ok, and does help compensate somewhat, but I am SO hoping that my eye will gradually return to something like normal before too long.

As soon as I can see well enough to do a proper first light I will be sure to do so!

Dave

[nicoscy]

Dave,

I am glad to have been of service to another Takahashi aficionado! 

I find it hilarious that when we are discussing binoviewers and fighting how to reduce the light path, it is possible to say that there is a (whopping) 15mm available in-travel ?

Enjoy viewing through both eyes and I hope your right eye settles down in respect of floaters. As we get older it becomes more challenging. 

I myself  got hit with presbyopia this year - in 3 short months, I can't see clearly from up close! Frustrating as I got an iPhone 8 6 months ago. Had this occurred a bit sooner, I would have bought the 8 Plus!. I took care of short myopia and astigmatism 14 years ago with LASIK, but there is no escaping presbyopia .