A poor man’s Mk5 binoviewer

[+bryand]

Key message: You can make Baader Glass Path Correctors work with a William Optics binoviewer.

 

I like using my William Optics binoviewer for the wide field of view it gives, but I resent having to give up view width to a Barlow just to get it to focus (I have 1.6X, 2.0X and 2.6X Barlows for it).  What I want is the widest possible view with edge-to-edge clarity using as much of my existing kit as possible.

The 20.3 mm Clear Aperture of the WO BV limits the eyepieces you can use without vignetting.

Before I invest in a new Maxbrite II or Mk 5 GrossSpendungsBinoViewer  I want to investigate whether I can get the sort of widefield view the 24 mm Panoptics would give in these, using my William Optics binoviewer and 19 mm Panoptics (which I already have).

Playing around with astronomy.tools’  field of view simulator indicates that the 24 mm eyepiece with a 1.6X Barlow is equivalent to a 19 mm eyepiece with a 1.25X Barlow, and the increased view gives to a useful amount of extra sky.  So the hunt was on for a 1.25X Barlow.  OK so Baader insist on calling it a Glass Path Corrector, but they make a version that fits inside their 2” T-2 nosepiece.  And I already have that on my WO bino.

RESULTS

Disappointing, in so far as the binoviewer refused to come to focus on my 132 mm WO refractor even at 0 mm extension with the GPC fitted to the end of the binoviewer.

However, the Baader website notes on the GPC indicate that if it is placed in front of the diagonal, rather than between the diagonal and binoviewer, you gain extra in-focus, so this is what I eventually tried.

I want to retain the Amici prism diagonal because it gives a right-way-up, right-way-round image, just like binoculars do.  I think this is one of the main reasons for using a binoviewer.  My APM diagonal has an SCT thread on the scope end, and I had an SCT to T-2 adapter which more or less fits.

The adapter reduces the clear aperture of the diagonal, but since I’m using 1¼” eyepieces anyway, that doesn’t matter.  But it would mean allocating that diagonal to binoviewer use only.  Can’t do that, so I’ll eventually need a special Amici prism diagonal just for the binoviewer.  Baader make one, and I’d need it if I upgraded to a MaxBrite or Mk 5 anyway so the diagonal and GPC wouldn’t be wasted.

 

 

 

Edited February 23, 2020 by bryand

[+Bino-viewer]

Bryan : next time we have a meet, i'll bring all my bino kit (i have 3 GPCs & 3 prisms including the standard Amici) and you can try it out

and see what works best. The FLT132 will work very well with binoviewers as it has plenty, more than enough backfocus for your needs, but you need to optimise your gear to do it.

 

The main problem here is the big APM Amici diagonal. Its a very nice bit of kit of course, but is far too big, and swallows up way too much 

lightpath i'm afraid to work well with binoviewers. The main culprit is the big 2" eyepiece holder which probably eats up 60 mm on its own.

I would keep that for monovision work with your big 2" eyepieces and use it for that exclusively.

It will actually work better with your SCT when binoviewing because you don't need any compensators at all to make focus.

On the flipside of that (and there is usually a compromise of sorts to be made with binoviewing) is that with such a long lightpath requirement you will lose aperture as a result,

as well as other issues, but thats another story.

 

You've already found out that you can make focus by putting your GPC into the scope side of the diagonal.

Problem is there, that the further you move the GPC away from the binoviewer, the magnification factor will increase exponentially.

Its probably working at 2 - 3x in your case. I'm sure it would work ok in the WO binoviewer nose, and its only the big diagonal thats stopping it from doing so.

 

So what to do ?

I have a Baader Amici which is T2 fitted both ends, and thats what you need, because it removes the lightpath eating eyepiece holder on the diagonal.

You could try a T2 clicklock  on the Baader diagonal and insert the WO Bino (with GPC or without) into it and see if it works. It may do ?

The Clicklocks are nice, but again they swallow up about 15mm of lightpath on their own.

All of the stated mm's here and there i mention may seem inconsequential, but it can actually be the difference between getting focus, or not. Millimetre's count !!

 

If you really want to get the lowest power widest field binoviewing setup ie natively sans GPC, the Baader system is the way to go and will work 

in all 'imaging optimised' (ie with plenty of back focus) refractors, or adding a 1.25gpc to make virtually every other type of refractor work ok.

 

The new Maxbright Mark 2 is long awaited, and has been revealed and looks very nice and is expected to be about a third the cost of a Mk 5.

The latest i've heard is that it will be released at the end of March.

 

 

 

[+Bino-viewer]

Baader Amici left, standard Baader prism on the right, both T2 compatible.

The Amici is quite a bit bigger and uses up an extra 10-15mm of lightpath, yet it will still come to focus comfortably without any extra amplification.

 

As short a lightpath as you can just about get (the Mk5 and short Baader prism take up around 150mm of lightpath)

This compares to your average 2" star diagonal that takes that much on its own before you even add a binoviewer.

I'm not using a GPC here and still have just over 20mm of in focus remaining.

 

The top image you'll notice my prism has a large smooth nosepiece.

A smoothbore nosepiece is much more secure than one with an undercut (including the Baader ones) 

as it gives the scopes compression ring much more purchase on the diagonal and weight of the binoviewer and eyepieces.

An undercut design can slip in the cold with the torque and weight of the bino system on it......with rather alarming results !

Edited February 23, 2020 by Bino-viewer

[+bryand]

Thanks for the excellent analysis Rob. 

I'd already concluded that I'll want a Baader T2 Amici prism eventually, it's just a matter of letting the inevitable sink in to lessen the financial pain! 

This is actually a sneaky plan to buy all the bits I'll need for a Baader setup, one at a time, till the final purchase doesn't hurt so much!

 

I'm in two minds about the Maxbrite II.  If I got one (or a Denkmeier/Earthwin) , would I be forever wondering if I'd have been better with a Mk 5?

 

[+Bino-viewer]

I'll be honest : the differences between the 2 (Maxbright and Mk 5) are fairly small.

Well, they were to me and my 50+ year old eyes when i upgraded from a Maxbright Mk 1 a few years ago.

 

The new Mk 2 version looks really nice. The eyepiece holders look nice as well.

And it appears it uses the same GPCs as the Mk5  and uses the same Zeiss micro-bayonet as well.

 

https://www.baader-planetarium.com/en/accessories/optical-accessories/bino-viewer/baader-maxbright-2-binoviewer-with-case.html

 

The Baader Amici i'm using is Baader item number 2456130 # 2  

See link below

 

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p608_Baader-90--Amici-Prism---with-T2-connection-on-both-sides.html

 

They also do a megabucks 2" version as well......

[tuckstar]

I use the baader gpc with my Williams.  Just put an adaptor on the binoviewer and stuck a quick changer on it so I can connect directly to the amici with gpc in place, no nose pieces, and another quick changer on to the scope back making the light path as short as possible. Couldn't get my 18.2 mm delites to focus with out gpc but no probs with it in place, although this does make them effectively about 10mm. Great for the moon.

this the adaptor I brought, https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F142579262765

but the specs are in the pictures

Edited February 24, 2020 by tuckstar

[tuckstar]

@bryand just remembered it was yourself who gave me the link to the adaptor!!

[Nightspore]

 

I have the WO bino. I use it with a 127mm Mak though so no real focusing problems. I only really look at the Moon and planets with it anyway. I also have a Baader Zeiss Amici with a clicklock fitted.

 

 

I even tried a set screw in it. Eventually I went with a WO helical Amici.

 

 

I turn the helical until it is tight and can't rotate for holding the bino. 

 

 

This is mainly to keep the overall weight down. It's not a bad Amici, not quite a Baader Zeiss of course, but good enough for the Moon.

Edited February 24, 2020 by Nightspore

[+bryand]

Here's an interim solution:

As Rob pointed out, the main problem is the APM diagonal, and in particular its huge eyepiece holder.

Turns out the holder is fitted with a 2" dovetail ring, retained by three grubscrews.  Also, Telescope Service supply a 2" dovetail -> T-2 adaptor ring, which allows me to bypass the eyepiece holder completely.

The 1.25X GPC fits into the adaptor, so comes after the prism, and the revised rig saves me about 40 mm backfocus.  Just need something at infinity to test it with...

 

 

[+Bino-viewer]

Thats looking good Bryan 😀

You've found a nice solution there, and i'm sure it will work.

 

The 40mm or so + the 18mm (or so) from the 1.25x gpc should be plenty.

You may even be able to focus without the gpc ; i bet it will be close ?

 

I remember having a similar dilemma when i brought my Herschel wedge a few years ago.

The wedge is big with the eyepiece holder and clicklock. Even bigger than your average 2" Amici diagonal.

 

 

Naturally, i wanted to fit a binoviewer on to it.

Thats whats so good about Baader. Its T2 options are comprehensive, there's so many ways and available adapters to get what you need.

In this case the big clicklock and eyepiece holder are simply removed and replaced with a T2 quickchanger which is of course threaded to hold

the required filters inside.

 

 

Then simply add binoviewer and you're away.

And with the Mk5 (and new Maxbright 2) you add the GPC (either the 1.25 or 1.7x) into the back of the binoviewer itself

to enable you to focus. One of them in this case is almost certain to be required as theres still a lot of lightpath here.

And a gpc is good here for another reason : it will correct for prism induced spherochromatism as well.

The sun looks great through a refractor / wedge and binoviewers !!

 

Edited March 6, 2020 by Bino-viewer

[+bryand]

3 hours ago, Bino-viewer said:

Thats looking good Bryan 😀

You've found a nice solution there, and i'm sure it will work.

 

The 40mm or so + the 18mm (or so) from the 1.25x gpc should be plenty.

You may even be able to focus without the gpc ; i bet it will be close ?

Certainly does work! 

Tried it on the Moon and M45 tonight and I got perfect focus with 18mm focuser extension with the 19mm Panoptics and 12mm extension with the Pentax 12mm XFs.

Well pleased: best view ever with the Pentax XFs, but could only get 4 stars in the Trapezium.

Didn't try it without the GPC, which I think will become a permanent fixture.