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For those who are interested and use a bino with a schmidt cas scope and are concerned about back focus issues. My bino is a Andrews unit, it works very well indeed. It has a light path of 100mm. I bought a William Optics 1.6x barlow nosepiece to use with it. I have two 1.25 inch diagonals. The standard Celestron prism and a Long Perng dielectric. The Celestron prism has a light path of 65mm, the dielectric 95mm. Using the 1.6 barlow screwed into the bino with the prism diagonal, you need an extra 59mm of infocus, or backfocus depending how you want to look at it. If you place the barlow in the front of that diagonal, it negates the light path of the bino almost spot on. So it places the focal plane of my C8 back to the standard f/10 position. By pushing the barlow further into the lightpath this way its power is increased to about 1.8x. The increased contrast on luna detail is much better for me using a bino than mono, much more noticeable than using more expensive eyepieces in mono. Please note I am 62 years young and have more floaters than when younger, but am sure those with more youth would see improvements as well.
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