Useful CA

Hope someone can help answer this question. And please, I'm not trying to start up any turf wars.

A little background. I currently own a pair of BNs and am pleased with them. But like most of you, I'm always planning my next upgrade. I've been thinking of purchasing the 30mm Echelon so I can get some more photons and keep the cost down by continuing to use my current BN OCA's. My question is on the 1 1/4 inch technology and not the 2 inch format. Since Uncle Al says that the maximum 1 1/4 inch CA is 27mm is there any benefit in going beyond 27mm (eg 30mm) CA for a 1 1/4 format binoviewer?

Larry

Hi Larry,



In theory yes, because the aperture restriction is ahead of the focal plane where the diameter of the light cone is larger. Thus a larger clear aperture (note, CA also stands for chromatic aberration) will improve the illumination of edge objects in your 27mm field stop ep's. I highly recommend Rick Shaffer's excellent diagram in his tutorial on exit pupils, 'Wild Card 001' in the articles section of Astromart to see why this happens.

How noticeable it will be is a separate question given to some debate...

Milt