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Binoviewer Glasspath Correcter Questions

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9 replies to this topic

#1 elwaine

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Posted 18 September 2019 - 05:27 PM

Before asking my questions, I want to present the reason for my dilemma. 

 

I recently purchased a nice binoviewer that appears to lack a way to add a Baader Glasspath Corrector between the binoviewer and a T-2 prism diagonal. On the telescope side of the "Zeiss" binoviewer, the metal base ring of a Baader Quick Changer does not attach directly to the binoviewer body. Instead, it is held firmly in place by an inner ring that screws into the binoviewer body, thereby holding the Quick Changer base in place.

 

med_gallery_17233_3964_83633.jpg

There are no threads inside the steel base of the Quick Changer, and even if there were, the black metal ring doesn't permit a GPC to be inserted into the opening of the base of the quick changer, as the black ring is about the same diameter as the GPC.

 

I thought I would prefer this arrangement: Binoviewer > Baader Glasspath Corrector > T-2 Quick Changer > T-2 prism > T-2 to 2” nose piece > telescope. But I have been advised that the only way to use a Baader GPC with my binoviewer is to use this arrangement: Binoviewer > Quick Changer > T-2 prism diagonal > GPC inside a T-2 to 1.25” nosepiece adapter > telescope.

 

This is my problem: my primary interest is viewing the Moon and Planets. I want to use the binoviewer exclusively with my 2700mm focal length Mak. I'd also like to use a pair of Morpheus 17.5mm eps. I'll be able to reach focus with the Bino-system, as described in my preferred arrangement (above) without using any GPCs. I will get a base magnification of approx. 156x, which would be ideal for a lot of my viewing. However, there will be times that I would like to increase the magnification to about 200x (with a 1.25x GPC) and to about 260x (with a 1.7x GPC). But those options are apparently off the table with my particular binoviewer.  

 

If, instead of using GPCs, I could use a BARCON or BARADV screwed into a 2" nosepiece, but that would yield a magnification of approximately 400x, and that is more magnification than I want. I do not enjoy viewing with tiny exit pupils. So I was thinking of buying a 1.25x and a 1.7x GPC, attaching each to it's own T-2 to 1.25" nosepiece adapter. In that case, I'd be using arrangement #2 (Binoviewer > Quick Changer > T-2 prism diagonal > GPC inside a T-2 to 1.25” nosepiece > telescope.

 

So (finally) here are my questions:

1) Will the GPCs work using them in the above chain of alignment?

2) If they will work, by placing the GPCs in front the T-2 prism, closer to the telescope - how much more magnification (and decrease in f.o.v.) will those 2 GPCs yield?

3) Instead of using a GPC or a Barlow, would I be better off buying a second pair of shorter FL eyepieces to achieve higher magnification?

4) Are there other solutions you can suggest?

 

Thanks in advance.


Edited by elwaine, 18 September 2019 - 05:31 PM.


#2 Eddgie

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Posted 18 September 2019 - 07:49 PM

There are two ways to mount the GPC.  The Mark V uses threads inside the dovetail, and your BV does not seem to have a provision for this.

 

With other T2 systems (like the Maxbright), the GPC mounts into the top of the T2 diagonal.  To do this, you have to make sure the lenses in the GPC are facing the right direction.  There is a little label on the side of the GPC that tells you which side the convex lenses have to face (as I recall, towards the telescope).

 

The quick change ring (or the T2 female ring in the case of the Maxbright or T2 modified binoviewers) screws on over the top of the GPC flange securing the GPC in place.

 

So, the GPC mounts in the top of the T2 prism, and you screw your quick change connector over the top to hold it in place.

 

Does this make sense?


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#3 elwaine

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Posted 18 September 2019 - 08:32 PM

Thanks, Ed. That does make sense. Without having all of the parts on hand (some are back ordered), I didn't think of that possibility. 

 

I just did another Google search and found that one of our members (suburbanskies) posted this photo, showing exactly what you described.



#4 Eddgie

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Posted 18 September 2019 - 08:33 PM

Yep, that's it.



#5 elwaine

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Posted 19 September 2019 - 08:27 AM

Ed, looking at the photo I notice that the orientation of the GPC is opposite to when it is installed into a Baader Mark V binoviewer.  The lens housing of the GPC, when installed into a Mark V, points toward the binoviewer. But when placed into a T-2 prism, and secured via a Quick Changer clamp, the lens housing of the GPC points toward the telescope. Do I need a Specific GPC for non-Mark V bino-viewer, or can the lens housing of GPC be reversed and screwed into its holder upside down?

 

gallery_6803_304_39628.jpg

 

Addendum: Baader makes 2 models of their 1.25x and 1.7x GPC. One is designed to be used with a Zeiss ring dovetail and the other with a T-2 thread. E.g., the 1.25x GPC  for T-2 thread is part # 2456314, and Zeiss ring model is part # 2456314Z. As best as I can tell, I need the model without the Z, which I think is for use with the Mark V "Giant" Binoviewer.


Edited by elwaine, 19 September 2019 - 09:04 AM.


#6 Eddgie

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Posted 19 September 2019 - 11:38 AM

No, I covered that in my first post.   If you look at the GPC, you will see a label and in tiny print, it tells you how to orient the lenses for non-Mark V use.

 

As I recall (and I am too lazy to go pull mine out of my solar scope diagonal) the convex lens side faces the sky.

 

There is a small retaining ring on the flange side.  You just remove the ring, tilt the lens out (it is a cemented lens) and flip it around (if it was oriented for the Mark V).  Put the ring back in, and away you go.

 

Since the Mark V is sold by Astro-Physics, if you buy a GPC from them, it is probably already set up for the Mark V.  I have bought several GPCs over the years from other vendors and all have been set up for the Maxbright (which is the orientation that you would need).  It is easy to change though. 


Edited by Eddgie, 19 September 2019 - 11:40 AM.

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#7 Jeff B

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Posted 20 September 2019 - 10:53 AM

Larry, I have the exact same issue with one of my viewers and like Eddgie said, you can just drop the GPC on top of the T2 thread, but be careful as there will a bit less depth available for the viewer's dovetail and the GPC can move around side to side a little. 

 

Like Eddgie says, you have to reverse the GPC element in its holder, which is really easy.  The GPC is a cemented doublet with one convex side which should be pointed at the scope's objective. 

 

Now you can screw the GPC into the T2 inside thread but that makes changing them out difficult so what I did was to install an "O" ring over the outside thread of the T2 adapter and then screwed the quick changer down on top of that.  This does two things, it allow me to position the the thumb screw orientation to my liking and it allows the GPC flange to sit further down and center itself in the bottom of the quick changer. This also allows easy installation and change out of the 1.25x and 1.7x GPCs as well as complete insertion and engagement of the viewer's dovetail with the quick changer.  Magnification levels will also be slightly higher than specified as the GPC element now sits a little further forward in the light path (but I don't loose any sleep over it)

 

I've always needed to McGiver something up when it comes to all of the GPC/OCS/viewer combinations I have.   I'd LOVE to have a GPC powerswitch!

 

Jeff



#8 elwaine

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Posted 20 September 2019 - 11:09 AM

Thanks Jeff. That's very helpful! 

 

I want to make sure I understand your directions. When you say "install an "O" ring over the outside thread of the T2 adapter" what adapter are you referring to? The male T-2 threads on the GPC?

 

If you have the time, a picture would be very helpful.


Edited by elwaine, 20 September 2019 - 11:29 AM.


#9 Jeff B

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Posted 20 September 2019 - 01:41 PM

Larry, in your picture above in post number 5, the thin "O" ring goes over the outside diameter threads of the threaded adapter post sticking up out of the top of the diagonal and flush against the top of the diagonal body, which is where you screw the quick changer on.  As you screw the quick changer in place, it will contact and compress the "O" ring giving you a bit of freedom to choose where the orientation of the thumbscrew ends up.  Now as the quick changer now sits up a little more (1-2mm) away from the top of the diagonal body, the thin outer flange of the GPC will actually sit down flush into the center hole of the quick changer, resting on top of the diagonal post, and centering itself there. 

 

The GPC will actually screw into the inner thread of that top post but if you want to change it out, you have to unscrew the quick changer to do that, which is not user friendly unless you are willing to basically dedicate that diagonal to that particular GPC (a rather expensive thing to do).

 

 

Jeff


Edited by Jeff B, 20 September 2019 - 01:42 PM.


#10 elwaine

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Posted 20 September 2019 - 04:26 PM

Gotcha. Thanks.




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