Lou H
Well-known member
I tried a number of my astronomical eyepieces on my Diascope 85 after purchasing the Zeiss adapter, which comprises a sleeve that converts the 1.25” eyepiece to the inside diameter of the ocular end of the scope and a threaded ring the holds the adapter in place. The eyepiece is retained in the sleeve with a set screw which if used, necessitates removing the whole thing to switch eyepieces.
First off, the focal plane of the body is inside the end of the body so the eyepieces must be inserted as far as they will go in order to focus at infinity. All the 1.25” eyepieces I have will come to focus, including a 9mm Nagler which yields 56x with an 82 degree apparent FOV and a 1.45 degree 78’@1000yds actual FOV compared to 1.15 degree 60’@1000yds of the Zeiss Vario zoom eyepiece. The longest 1.25” eyepiece I have is 24.5mm which yields about 20x. This eyepiece has a 67 degree apparent FOV and yields a whopping 3.35 degree 175’@1000yds actual FOV compared to the 2.5 degree 129’@1000yds of the Vario.
So, at each end of the magnification, the high-end astro eyepiece provide significantly wider fields of view compared to the Zeiss zoom, which is pretty much expected considering the compromises inherent in a zoom eyepiece. At high power the image quality was pretty much the same with the two eyepieces. What was interesting was that at 20x, the flatness of the image and edge sharpness were way better even with the wider FOV of the astro eyepiece. Evidently edge sharpness at low power is another compromise in the Zeiss zoom.
Unfortunately, with the position of the focal plane, it’s not really possible to use a Barlow so observing at powers great than 60 will require either very short focal length eyepieces or afocal coupling with another telescope.
First off, the focal plane of the body is inside the end of the body so the eyepieces must be inserted as far as they will go in order to focus at infinity. All the 1.25” eyepieces I have will come to focus, including a 9mm Nagler which yields 56x with an 82 degree apparent FOV and a 1.45 degree 78’@1000yds actual FOV compared to 1.15 degree 60’@1000yds of the Zeiss Vario zoom eyepiece. The longest 1.25” eyepiece I have is 24.5mm which yields about 20x. This eyepiece has a 67 degree apparent FOV and yields a whopping 3.35 degree 175’@1000yds actual FOV compared to the 2.5 degree 129’@1000yds of the Vario.
So, at each end of the magnification, the high-end astro eyepiece provide significantly wider fields of view compared to the Zeiss zoom, which is pretty much expected considering the compromises inherent in a zoom eyepiece. At high power the image quality was pretty much the same with the two eyepieces. What was interesting was that at 20x, the flatness of the image and edge sharpness were way better even with the wider FOV of the astro eyepiece. Evidently edge sharpness at low power is another compromise in the Zeiss zoom.
Unfortunately, with the position of the focal plane, it’s not really possible to use a Barlow so observing at powers great than 60 will require either very short focal length eyepieces or afocal coupling with another telescope.