Telescope Reviews: Effect of barlow on mags with bino

I've interchanged OCS/OCA from several different binoviewers. Stellervue, Burgess and Denkmeier OCS/OCA are all interchangable. Interesting to note the Denkmeier binoviewer with the Denkmeier OCS would NOT come to focus in my Megrez 80 refractor. However it DID focus when replaced with either the Stellervue OCS or the Burgess OCS.

I've also used these three binoviewers inserted into several barlows. However I've measurd the power factor when any of these BVs are inserted into a barlow from above 3.0x up to close to 4.0x. Barlows used included Televue 2x barlow, Celestron Ultima 2x barlow and Orion standard 2x barlow.

I've also tried fitting the optical nosepiece of these various barlows onto these three binoviewers. I've only found one barlow optical nose so far that works. That was the Orion 2x barlow (that I mentioned above) with chrome barrel and black nose piece. That barlow used normally resulted in 3.75x. When that barlow black nosepiece was screwed onto these various BVs, the power factor was ~2.8x in all three binoviewers.

Neither the Celestron Ultima barlow (doesn't have a nose, element is in the chrome sleeve) nor the Televue 2x barlow nose would screw onto the chrome sleeve hollow nose of any of these binoviewers. Therefore the only way to use them is to insert the binoviewer into the barlow. In all cases, moving the barlow further in front of the binoviewer increased the power.

If you intend to use a barlow, I would search for one that allows you to remove the barlow element nosepiece and screw it directly onto the binoviewer.

See this thread regarding use of barlows for an explanation of how you can calculate the power of your barlow/binoviewer combination.

edz

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