Has anyone had any experience with the 13mm Erfle eyepiece that was provided with Questar telescopes in the 1960s? I have one of these and was surprised to see four pointers in the eyepiece, coming in from four different sides. Has anyone else seen these? Does anyone know what they are there for?
13mm Questar Erfle eyepiece
Posted 21 February 2019 - 03:18 AM
From around 1950 to 1968 the 3.5’ Questar shipped with 2 Japanese made eyepieces usually marked 40-80X and 80-160X (sometimes without the “X”). Eyepiece classifications were a little fuzzier back then but the 40-80X was classified as a Koenig and about 26 mm and the 80-160X was classified as an Erfle and about 12 mm. They were standard equipment until around 1969 when Questar shifted to American made Brandon’s. As such, the Japanese eyepieces work just fine for those scopes. I have a 1964 and 1968 Questar each with both those eyepieces and a 2000 Questar that came with a number of Brandons. The first number in the 40-80X designation is the approximate magification and second number in is the approximate magnification when using the Questar internal Barlow (which could vary somewhat in magnification so it’s unlikely to be exactly 2X). You can also buy an adapter to use standard 1.25” eyepieces in these scopes.
The four “pointers” you speak of were a option and easy to add or remove from the bottom of the eyepieces (only 1 of my 4 Japanese eyepieces has this feature). They are essentially a partial crosshair to try and make centering of an object in the main scope/finder scope easier but your mileage may vary. Hope this answers your questions.
- terraclarke likes this
Posted 21 February 2019 - 08:41 AM
One note, the 40-80x and 80-160x were for the original 45.5” focal length. By early 1960s the main scope optics were listed as 50.5” focus so the actual magnifications are higher. That change might have been when they switched to Cumberland from Cave.
At 50.5” fl, the 80-160 is really 95-190 or so.
I did use my Celestron Microguide for star drift timings and my measured fl with main scope after my recent optics replacement came out at 1281mm and my Barlow is 1.98x.