Binoscope/Binoviewer with refractors

Strictly talking refractors; if I had a choice between a 6" APO with a quality binoviewer or a binoscope comprised of two 5" APOs. Which setup would transmit more light to the eyes? Visually, would it be that noticeable of a difference? I can tell the difference when using a binoviewer on my 5" APO as opposed to a single eyepiece but it got me wondering.

Greg,

A 5" scope has a light grasp of 19.6 square inches. A 6" scope has a light grasp of 28.3 square inches.

Given two lenses of a similar type the 6" will transmit more light than the 5" inch. A binoviewer will divide that light between the two eyes. A binoscope will not. The dual 5 inch should have a light grasp of 39.2 square inches. This would provide much more light.

I have a pair of Meade 90's I would like to make a binoscope out of. The problem is the IP distance will be at least 90mm with both scopes side by side. I am thinking about cutting the tubes so they will each focus with dual diagonals and putting my head in between the OTA's

Don Durbin

Greg,

I cannot answer your question, but I'd sure like to be a part of the testing. Let me know when and where

Just looking at the square inch issues:

5" x 2 = 38 sq inches (19 sq in / eye)
6" = 28 sq inches (14 sq in / eye without loss)

I think the 5" would be better. A better comparison might be a dual 4" to a binoviewer 6":

4" x 2 = 25 sq in (12.5 / eye)

So in that case, the 6" would be brighter and have more resolution. I'm thinking you can get two 4 inch APOs for less than one 6" APO, but I'm not certain.

Clear skies,

Tom