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Posts Made By: Donald Durbin

October 21, 2007 08:45 PM Forum: Binoviewers

BinoVue on a DOB??

Posted By Donald Durbin
John,

You will need an optical corrector. A typical DOB OCA is a combination of a focal reducer and a barlow element.

Siebert sells these. Burgess also has a corrector that will work. The thing about a corrector is that it will add magnification. The lower the magnification added, the higher the cost of the corrector.

Don Durbin


October 31, 2007 03:38 PM Forum: Binoviewers

Binoviewer problem: stars are sea gulls : (

Posted By Donald Durbin
Kumar,

I think you problem is too much magnification. By using the extension tube you are able to come to focus, but the further away you position the 1.9X element the more magnified the view.

Is there any chance you have or can borrow a focal reducer in a 1 /14" filter cell? I think both SAC and Scopestuff sell these. If you know anyone who uses a CCD camera, they may have one that they use with the camera.

Anacortes sells one also but I think the .5x may be a little too much power. You cannot have the power of the focal reducer exceed the power of the barlow element. In this case the .5 would match to 2.0x barlow or greater.

http://www.buytelescopes.com/product.asp?t=&pid=12533&m=

If you can get your hands on one of these, try screwing the focal reducer into the binoviewer and the tube with the 1.9X corrector into that. This will give you a basic OCA with a lower magnification power.

Don

November 11, 2007 10:05 PM Forum: Binoviewers

Binoviewing with a Meade 127ED

Posted By Donald Durbin
Hi Peter,

You will need an OCS or an OCA to reach focus. A barlow will work also but the magnification will be high.

The typical setup for a refractor is to place a barlow or magnifying element in front of your diagonal with a focal reducer attached to your binoviewer. If you leave out the focal reducer you should still focus but as I said the magnification will be high.

Don Durbin

November 28, 2007 03:48 AM Forum: Binoviewers

Edmund Optics Orthos

Posted By Donald Durbin
Hi Brian,

I have a pair of 9mm HD Orthos that I think are pretty good. I think they are from University Optics.

Don

December 15, 2007 11:25 PM Forum: Binoviewers

Powermates Barlows and OCA's

Posted By Donald Durbin
Hi Doug,

I was hoping someone else would jump on this, but since there has been no response, I will take a stab at it.

A simple Barlow is a single element device that increases magnification. While they amplified the magnification of your telescope, they also played havoc with eye-relief. The two element Barlow was the first to do more than increase magnification without degrading the optics of your telescope. The telenegative Barlow was a three element system. The powermate is a four element system.


The OCA or OCS depending on the manufacture is a multi-element device that was primarily designed to overcome the long light path of the binoviewer by altering the light cone. This can be done with a simple single element Barlow but the magnification quickly becomes too high with that approach. The typical OCA or OCS consists of a combination of Barlow elements and focal reducer elements. This combination controls the level of magnification.

Don Durbin


December 28, 2007 01:34 AM Forum: Chinese Optics Imports

New Forum Name

Posted By Donald Durbin
Gene,

No one is trying to hide where this forum came from. This forum was originally Burgess Optics. It is now the Chinese Optics Imports forum.

Don

January 3, 2008 02:55 AM Forum: Binoviewers

BV's and neb filters

Posted By Donald Durbin
Hi All,

I have used an O3 filter with my Burgess 24mm and a focal reducer on my C9.25. That is a pretty good combination. Both Siebert and Denk have focal reducers that work great with an SCT and binoviewers. The 100mm light path binoviewers like Burgess and others make focusing easy.

If you use the largest EP that you can, depending on how much vignetting you can stand and you add to that a focal reducer you can get a nice wide field with plenty of light to use with your nebula filters.

Don

February 18, 2008 10:57 PM Forum: Binoviewers

TAK TOA130 & Denkmier Binoviewer Combo?

Posted By Donald Durbin
Hi Louis,

First try using a 1 1/4" diagonal instead of a 2". My FS-128 works with my Denk with a 1 1/4" LumiBrite Diagonal.

Second try going without the diagonal. It is great for terrestrial viewing but a pain in the neck for most astronomy applications. grin

Third if you have a powerswitch on the binoviewer, taking it off gains an a bit more in-focus.

Forth, try different types of EPs. You can see which ones come to focus sooner by just using each one with a diagonal. The further out you end up, the better chance you will focus in your binoviewer.

Good Luck,
Don

June 27, 2008 02:36 PM Forum: Binoviewers

Whither Binoviewers

Posted By Donald Durbin
Hi Rod,

Still waiting for someone to review the Earth Win Binoviewers.

There are some other items I have heard of and I am waiting on but I do not want to speculate on them.

Don Durbin


November 3, 2008 01:14 AM Forum: Binoviewers

Best Bino and eyepieces for 14.5 Starmaster?

Posted By Donald Durbin
Hi Mark,

You will not be able to focus a binoviewer without an optical corrector. Most binoviewer dealers have either OCA or OCS systems for this purpose.

The Earthwin might be a good choice for you. I have not been able to figure out the weight of that unit but the built in optical corrector should allow you to come to focus.

The problem with a lot of the OCS or OCA systems out there is the amount of magnification that they add. Binoviewers are also limited by a combination of their clear aperture and light path to EPs with a focal length of 24mm or less. Going over that results in a vignetted view which a lot of people find objectionable.

The best thing you could do is try to borrow different models and see how they work in your scope.

Don Durbin

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