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William Optic Binoviewer used with a Sky-Watcher Evostar ED Telescope

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#1 mondo1948

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Posted 09 June 2021 - 04:21 PM

I know some of what I'm going to say has already been said in several places on this forum, but for the purpose of my discussion, I will summarize some things.

 

The William Optics binoviewer, coupled with the 1.6 OCA that is supplied with the binoviewer, will not allow the SW 100 ED to come to focus.

 

One answer is to buy a Barlow that allows you to remove the 2x "cell" from the Barlow and attach that to the WO binoviewer.  That works.  I know because I tried it but it creates a lot of extra magnification...maybe 3.5-4X, I've been led to believe.  I'm not happy with this solution because I don't like the significant increase in magnification.

 

Another answer is to buy a 1.25" diagonal and screw the 1.6 OCA into the front of the diagonal, closest to the objective lens.  This, I'm told, will yield more than 1.6x power; maybe around 2.1x.  Again, more power than some of us would like.

 

Now, let's look at Siebert Optics solutions:

 

They have an OCA that will increase the power only 1.25x, however, in order to use it, you will need a 1.25" diagonal.  The OCA is $199.00 plus the cost of a 1.25" diagonal, if you don't already have one.

 

Siebert also has a "low profile" modified diagonal with a corrector that apparently will add NO extra magnification and attaches directly to the WO binoviewer and it will fit the 2" focuser on the SW 100 scope.  This solution is $199.00 and obviously, you won't need to buy a 1.25" diagonal.

 

I kind of like the 2nd solution from Sieberts but wonder if anyone has tried it and can guarantee me that the SW100 ED will focus properly.  

 

While I like the 2nd Siebert's solution,  I'm not sure I want to do all my binoviewing through a 1.25" diagonal.....won't something be lost?  I'm assuming that what would be lost are the benefits 2" diagonals bring to the table, right?

 

Thanks for any help you can provide,

Mondo



#2 Alrakis

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Posted 09 June 2021 - 04:47 PM

Mondo,

 

A more simple solution is to change the focuser. In order to accommodate either a binoviewer or a herscel wedge I changed to a GSO linear bearing focuser:

 

https://agenaastro.c...cuser-96mm.html

 

This nets you about 35mm extra in focus. You would then need a 35mm extension for single eye viewing. 

 

Chris 



#3 mondo1948

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Posted 09 June 2021 - 05:02 PM

Mondo,

 

A more simple solution is to change the focuser. In order to accommodate either a binoviewer or a herscel wedge I changed to a GSO linear bearing focuser:

 

https://agenaastro.c...cuser-96mm.html

 

This nets you about 35mm extra in focus. You would then need a 35mm extension for single eye viewing. 

 

Chris 

 

Hi Chris,

What is a 35mm extension?

Also, wouldn't adding the new focuser still need the 1.6x OCA, resulting in an additonal 1.6x magnification?

 

Thanks,

Mondo

 

 



#4 Alrakis

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Posted 09 June 2021 - 05:19 PM

Mondo,

 

An extension is this:

 

https://agenaastro.c...-extension.html

 

Which is needed with the 2" diagonal to see with one eye.

 

So, without the extension your optical path length is 35mm shorter. Depending on the eyepieces you might be able to use the binoviewer without the 1.6x OCA. If you need a bit more in focus I would (and do) use a 1 1/4" prism diagonal. Compared to a 2“ mirror diagonal (about 110mm optical path length), a 1 1/4" (or T2) prism diagonal has an optical path length about 40mm shorter (about 70mm optical path length).

 

This means that essentially using a different focuser and a different diagonal will bring your binoviewer an equivalent of 75mm closer to the lens. This should negate the need for a barlow for most eyepieces.

 

Chris 



#5 eyespy

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Posted 10 June 2021 - 11:24 AM

Hi Mondo,

 

The average binoviewer is pretty restricted anyway and I doubt that you will notice any loss with a shorter path 1.25” diagonal.  I usually use mine for narrower field objects anyway so it becomes a bit of a non issue. 

 

Doug.....


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#6 sonny.barile

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Posted 10 June 2021 - 09:22 PM

Hi Mondo.    The WO has a 1.25 diameter nose piece, uses 1.25 diameter EP’s, and has a 20mm prism. I’m not sure you are getting any benefit other than mechanical strength from using a 2 inch diagonal at the eyepiece.

 

In my opinion a 1.25 diagonal is the better option. You would have two options as to where you can put the 1.6x.  The nose piece of the Bino and the insertion tube of the 1.25 diagonal.


Edited by sonny.barile, 10 June 2021 - 09:34 PM.


#7 mondo1948

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Posted 15 June 2021 - 04:59 PM

Hi Mondo.    The WO has a 1.25 diameter nose piece, uses 1.25 diameter EP’s, and has a 20mm prism. I’m not sure you are getting any benefit other than mechanical strength from using a 2 inch diagonal at the eyepiece.

 

In my opinion a 1.25 diagonal is the better option. You would have two options as to where you can put the 1.6x.  The nose piece of the Bino and the insertion tube of the 1.25 diagonal.

Hi Sonny,

Remeber though that I tried placing the 1.6 supplied OCA in the nose piece of the Bino and couldn't come to focus.  However, I will probably go ahead and get a 1.25" diagonal and place the 1.6 OCA in front of the diagonal, towards the objective lens.

 

Thank you,

Mondo


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#8 eyespy

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Posted 15 June 2021 - 05:35 PM

Hi Mondo,

 

You could try it attached to the bino first in order to avoid an excessive power increase.

 

Doug.....



#9 mondo1948

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Posted 15 June 2021 - 09:31 PM

Hi Mondo,

 

You could try it attached to the bino first in order to avoid an excessive power increase.

 

Doug.....

Hi Doug,

I did try putting the 1.6 OCA the day I got it with the binoviewer and my telescope wouldn't focus....that's why I bought a 2x Barlow, removed the cell, and attached it to the binoviewer, resulting in my focusing okay.

 

Mondo




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