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Native binoviewing with an ED127 - so close....

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#1 precaud

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Posted 11 September 2019 - 11:28 AM

Last month I had reasonably good results using the Omegon binoviewers with a SW180 Mak, with no OCS/barlow/amplifier (hereby called OCS for short). I say "reasonably good", because the views are restricted to relatively high magnifications, dictated primarily by the long focal length of the SW180, and my desire for BVing is mostly for low-mag, wider-field views.

 

So now I'll try to get the BV-sans-OCS to work with the ES ED127. The difference in focal length (950mm vs 2700mm) should give a threefold improvement in field width.

 

This pic shows the baseline setup, the one used for mono-viewing: A 37mm extension tube; the 2" eyepiece holder; a 2" diagonal; and a 1.25" adapter.

 

 

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#2 precaud

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Posted 11 September 2019 - 11:41 AM

The challenge now is to remove approx. 100mm of light path to accomodate the BVer.

 

The 37mm extension is removed. The 2" mirrored diagonal is replaced by the smallest 1.25" prism diagonal I have on hand. And the 10mm-high 1.25" adapter is replaced by one that adds only 5mm of height. This is the shortest light path that I can assemble.

 

The net result: It very nearly comes to focus. I estimate it is only 2 or 3mm away from it.

 

So where can I get another few mm from?

 

At 5mm, the 1.25" adapter is the shortest I have ever seen.

 

The old Celestron diagonal is the smallest I have ever seen. Body a tad smaller than recent ones, and its eyepiece holder a mm or so shorter.

 

It's hard to conceive of a shorter 2" holder for the drawtube.

 

Any ideas?

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#3 Garthid

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Posted 11 September 2019 - 12:19 PM

Have you looked at the light path length of different diagonals? I've read that not all prism diagonals have the same length.

Clear skies


Edited by Garthid, 11 September 2019 - 12:21 PM.


#4 precaud

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Posted 11 September 2019 - 12:24 PM

I have three of them here, this one is the shortest. I don't know about others. Do you have a link to info on it?



#5 Garthid

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Posted 11 September 2019 - 12:41 PM

http://www.baader-pl...14-03-06_v2.pdf

Look for the bar graph.



#6 noisejammer

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Posted 11 September 2019 - 12:54 PM

I suggest a Baader T2 prism - there are two models, so pick the one that suits your budget. You will need to purchase a 2" to T2 adapter.

 

Then lose the binoviewer's nosepiece and install a T2-binoviewer adapter from Raf Camera. Overall, this will gain you around 12-15 mm.



#7 precaud

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Posted 11 September 2019 - 01:33 PM

http://www.baader-pl...14-03-06_v2.pdf

Look for the bar graph.

 

Thanks for the linik, very useful info.

 

Unfortunately the one I'm using is the shortest one on the list; an older Celestron-branded Vixen.



#8 precaud

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Posted 11 September 2019 - 01:43 PM

I suggest a Baader T2 prism - there are two models, so pick the one that suits your budget. You will need to purchase a 2" to T2 adapter.

 

Then lose the binoviewer's nosepiece and install a T2-binoviewer adapter from Raf Camera. Overall, this will gain you around 12-15 mm.

I had a T2 and sold it. The prism quality was not as good as my others. And the path length was the same as a couple other prism diagonals I have, and longer than one of them.

 

I still have the T2 to 2" adapter here, and it has 3mm mounting thickness. So there is a possible 2mm to be had there, but the diagonal body itself was inherently longer. So this adapter would make it still longer than the Vixen.

 

Since the BV mounts flush to the eyepiece holder of the diagonal, I don't see how changing the nosepiece gains anything.


Edited by precaud, 11 September 2019 - 01:48 PM.


#9 precaud

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Posted 11 September 2019 - 01:47 PM

One question I have is about the height of the eyepiece holders on the Omegon BVs. They are the twist-lock collet type. Are those inherently taller than the simpler setscrew type used on other models?


Edited by precaud, 11 September 2019 - 01:49 PM.


#10 Eddgie

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Posted 11 September 2019 - 07:50 PM

I had an ES 127 and to reach focus, I needed to use the Baader standard prism, and I had to use a binoviewer that was connected directly to the top of the prism (Mark V).  Anything shorter than the Mark V should reach focus in this configuration.



#11 noisejammer

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Posted 11 September 2019 - 08:06 PM

Since the BV mounts flush to the eyepiece holder of the diagonal, I don't see how changing the nosepiece gains anything.

Here's your problem - the nosepiece is about 20mm long that is wasted offset that you can eliminate by getting one of the suggested adapters.

 

On your comment about the quality of Baader prisms - my Zeiss spec one (this one) is the best diagonal I own. I've compared it with my Astrophysics Maxbright, Baader Maxbright, Tak mirror and Tak prism.



#12 precaud

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Posted 11 September 2019 - 09:39 PM

Here's your problem - the nosepiece is about 20mm long that is wasted offset that you can eliminate by getting one of the suggested adapters.

 

I'l keep that in mind, but that would be a last-resort solution for me. Which adapter is it? There's 28 of 'em at that link.
 

On your comment about the quality of Baader prisms - my Zeiss spec one (this one) is the best diagonal I own. I've compared it with my Astrophysics Maxbright, Baader Maxbright, Tak mirror and Tak prism.

I'm glad you got a good one; mine wasn't. Measurements confirmed it:

https://www.cloudyni...ms&section=user



#13 precaud

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Posted 11 September 2019 - 09:43 PM

I had an ES 127 and to reach focus, I needed to use the Baader standard prism, and I had to use a binoviewer that was connected directly to the top of the prism (Mark V).

Yes, I remember reading about that. I guess what noisejammer is suggesting would come close to that.



#14 noisejammer

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Posted 11 September 2019 - 11:57 PM

The adapter has to suit your binoviewers. I don't know what thread your binoviewers have so I can't tell you.



#15 precaud

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Posted 12 September 2019 - 07:19 AM

The adapter has to suit your binoviewers. I don't know what thread your binoviewers have so I can't tell you.

As described inthe opening post, I have the Omegon BV's, same as the Arcturus and others.

 

EDIT: OK, never mind, I see the options now.

 

I think, because of its metal body, the Baader T2 diagonal is probably the only choice here.


Edited by precaud, 12 September 2019 - 08:54 AM.


#16 REC

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Posted 12 September 2019 - 12:52 PM

Last month I had reasonably good results using the Omegon binoviewers with a SW180 Mak, with no OCS/barlow/amplifier (hereby called OCS for short). I say "reasonably good", because the views are restricted to relatively high magnifications, dictated primarily by the long focal length of the SW180, and my desire for BVing is mostly for low-mag, wider-field views.

 

So now I'll try to get the BV-sans-OCS to work with the ES ED127. The difference in focal length (950mm vs 2700mm) should give a threefold improvement in field width.

 

This pic shows the baseline setup, the one used for mono-viewing: A 37mm extension tube; the 2" eyepiece holder; a 2" diagonal; and a 1.25" adapter.

I also like lower power and wider star fields. My C102mm f/1000 comes to focus without any OCS, so I keep the native focal length. I changed the stock R&P focuser for a bigger 10:1 WO focuser and that did the trick. With my pair of Meade 28mm SP I get down to 36x.


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#17 REC

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Posted 12 September 2019 - 12:55 PM

I suggest a Baader T2 prism - there are two models, so pick the one that suits your budget. You will need to purchase a 2" to T2 adapter.

 

Then lose the binoviewer's nosepiece and install a T2-binoviewer adapter from Raf Camera. Overall, this will gain you around 12-15 mm.

That's how I did it with my C102. Baader T2 prism, RAF adapter and eleminate the BV nose piece. Have lot's of room now and no OCS.



#18 precaud

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Posted 12 September 2019 - 02:22 PM

I also like lower power and wider star fields. My C102mm f/1000 comes to focus without any OCS, so I keep the native focal length. I changed the stock R&P focuser for a bigger 10:1 WO focuser and that did the trick. With my pair of Meade 28mm SP I get down to 36x.

 

Thanks for weighing in, REC. I have read some of your posts re: using your BV's sans OCS with a C102. I have a C102 as well and was going to try it, but assumed that 4" was not going to be enough aperture and result in dim images. I guess you find otherwise?

 

Did the WO focuser give you more in-travel over the stock R&P (which appears to have a very long throw...) ?



#19 Spikey131

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Posted 13 September 2019 - 05:58 PM

That's how I did it with my C102. Baader T2 prism, RAF adapter and eleminate the BV nose piece. Have lot's of room now and no OCS.

And if this doesn’t do it, you could add a Baader 1.25 GC inside the diagonal.



#20 precaud

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Posted 13 September 2019 - 07:09 PM

And if this doesn’t do it, you could add a Baader 1.25 GC inside the diagonal.

 

What's a "GC" ?



#21 Kunama

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Posted 13 September 2019 - 09:49 PM

GPC ... glass path corrector



#22 precaud

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Posted 13 September 2019 - 10:05 PM

Ah, that...

 

The intention was to be free of GPC''s, magnifiers, OCS's, barlows, whatever other name they can go by. But perhaps it's worth asking: what is the lowest-magnification one available?



#23 Kunama

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Posted 13 September 2019 - 11:07 PM

Ah, that...

 

The intention was to be free of GPC''s, magnifiers, OCS's, barlows, whatever other name they can go by. But perhaps it's worth asking: what is the lowest-magnification one available?

 

The GWK1.25 for the Baader T2 Zeiss prism or the T2 Maxbright magnification is 1.25x, light path requirement reduction 20mm.  The other main reason for having one is that it is designed to correct (somewhat) for the spherochromatism that the binoviewer introduces


Edited by Kunama, 13 September 2019 - 11:08 PM.


#24 precaud

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Posted 14 September 2019 - 08:54 AM

Ah, but we don't have a Baader diagonal here. What's the lowest with standard 1.25" filter threads?



#25 Eddgie

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Posted 14 September 2019 - 01:29 PM

As I said earlier, reaching focus with even a Mark V is easy if you go with a T2 diagonal and directly connect the binoviewer to the top of the diagonal.

 

I did this with my 127ED and reached focus with standard eyepieces without trouble using the Mark V, which has a much longer light path than the Arcturus.

We have all told you how you can do it, and in order to do it without modifying the telescope, the only solution that I know that works at native focal lenght is to use the T2 diagonal with a direct connect binoviewer.

 

post-14923-0-47164200-1416590818_thumb.jpg

 

The diagonal is about $140.  The adapter for the Arcturus is about $20.  




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