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Celestron/Orion Binoviewer for Newt/Dob

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#1 Stargazer3236


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Posted 02 April 2013 - 11:22 PM

I am curious, I want to use a binoviewer on my Orion XT10 and XX14g. Would either of those binoviewer work? If not, why? I am kind of new to binoviewing in a telescope. I know they work great for SCT's and Refractor's, but not for Newts?

Thanks for your feedback.

#2 hdt



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Posted 03 April 2013 - 12:50 AM

Hello, DG,

No optical reason why not. Ergonomically--you may not want to use a binoviewer on a telescope where the binoviewer is mounted where its orientation may change in more than 1 axis. (So, if you mount an SCT or refractor on an equatorial mount, you may not really want the binoviewers, for example).

Although Dobsonian mounts are alt-az, depending on the size of the Dobsonian, it may be difficult to place the binoviewer at a convenient location.

Think about a single eyepiece--to put one eye into the eyepiece, you have a lot more freedom to adjust your position relative to the scope. To put *both* eyes into two eyepieces which are fixed to the scope? You may need to turn your body and your neck.



p.s. and welcome to CloudyNights!

#3 sopticals


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Posted 03 April 2013 - 02:18 AM

Hi DG Aucoin, :)

I use a Williams Optics binoviewer with my 14" f5.08 dob. I have no problem regarding eye placement. My focuser is on the LHS of OTA, orientated around 30-35deg above horizontal, which in fact allows for a very comfortable viewing position. The one thing I had to do, was reduce the distance :bawling: between primary and secondary mirrors by approximately 1 3/4", to get enough back focus. However the adjustment was well worth the effort, and the views of moon and planets at 200x to 300x are exquisite :jump:. With two eyes resolution IMO, is up around 50% on mono viewing at the same image scale.


#4 Eddgie


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Posted 03 April 2013 - 08:01 AM

The answer abover are "Qualified" and the most important qualification here is that binoviewers may not work for you unless you either modify your telescope (moving the morror mounting cell forward in the tube) or use a binoviewer that comes with some kind of optical corrector or glass path correcter which allows you to reach focus.

While Stephen only needed to move his mirror a short distance, this may not be the case in all telescopes.

In some telescopes the mirror may have to be moved much further forward (as far as 4 inches), or get a set of truss poles and shorten them up by 4 inches.

And the issue with this is that if you move the mirror to far forward, you can cut down the aperture of you telecope because off axis light can no longer hit the edge of the secondary and then reflect back to the center of the field. You might wind up reducing the apeture with this change.

All of that is possible, but it is of course dependent on your ability and desire to make the necessary changes.

The second way this is normally done is to use a special corrector called an Newtonian OCS. This is a barrel and lens that screw on to the front of the binoviwer and extend down into the focuser tube.

Some small units come with a special barlow lens (usuallyl 1.25") that you put the binoviewer in to, then you use a 2" to 1.25" adapter on your focuser and use the bino/barlow in that .

The problem with this approach is that it usually locks you into pretty high power.

If your 10" scope is f/5 is 1250mm for example, and you barlow it 1.6x to reach focus, you are now using a scope that is 2000mm.

This means that if you use an eyepeice with a 21mm field stop ( maybe a 25mm Plossl ) your lowest power will be 80x and your biggest true field will be about .62 degrees or so.

So you can do it, but it requires that you pick your poision.

Modify the telescope by moving mirrors closer together and maybe replacing the secondary, or using some kind of OCS or barlow and loosing the ability to produce a low power field.

So, you can do it, and I recommend binoviewing especially if you enjoy planetary observing, but you need to figure out what approach you are going to take.

#5 sopticals


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Posted 04 April 2013 - 08:31 PM

As Eddgie has mentioned, you may have to increase the size of your secondary, to catch the full light cone. In my case for my 14" dob, I replaced my 2.76" GSO secondary with a 3.1" from Hubble Optics, to insure no aperture was lost from the primary. I will add also, that the HO secondary gave me a sharper view, (mono and bino), than the GSO item.


#6 Eddgie


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Posted 05 April 2013 - 09:03 AM

Yes, this is a good example, and one can see that it is a minor compromise.

The total obstrucion (including about 2% fo the spider vanes) is still under 25%, but now, the image will remain fully illuminated at the center of the field.

There are Newtonian programs that one can download free that the OP could use to determine the correct size secondary.

I am considering this myself. I have been wanting the 12" Oroin Go-To dob, and if I get it, I want to convert it to bino use.

Maybe. I go back and forth lately on binoviewers for deep sky. Love them for planets, but sometimes I miss the expansiveness of Naglers.

#7 SteveSMS


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Posted 05 April 2013 - 09:41 AM

Hi DG,

Before you modify your scope in any way do yourself a favor and contact Harry Siebert at Siebertoptics. I have used his correctors (OCAs) for many years and I have no problem recommending them. I use binoviewers in two different Newts with Siebert OCAs with zero modifications to either scope. There may be some compromises with regard to overall light throughput or vignetting but, for me, the two eyed view is too spectacular to worry about such things. YMMV.

Clear Skies,


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