How can you tell if you have an early Astroscan
Posted 02 July 2013 - 05:12 PM
Posted 02 July 2013 - 05:30 PM
Posted 02 July 2013 - 07:05 PM
The chrome eyepiece focuser tube has a Aluminum ring with a brass thumb screw to hold the eyepiece in, and what appears to be a Barlow or some sort of corrector lens at the bottom of the chrome tube.
hmmm ... That sounds like a modification by a previous owner. Can you post a pic? It would be interesting to see the mod.
Did the early ones come with a finder?
The early ones did not.
Fred Janicke ('amicus sidera' on this forum) produced an excellent article on Edmund history including the Astroscan. Here is the link: http://www.classicte...m/articles.html
Posted 03 July 2013 - 12:39 AM
Posted 03 July 2013 - 07:11 AM
Tom, that sure is an early one, from 1976; is that base a shiny silver, or more a grey color? The earliest ones had grey bases before they went to tan. If yours is grey, and is original, that would mean that almost all of the Astroscan bases made in that first run of 3000 were that color, and that the changeover to tan occurred in early 1977. Any chane you could post a photo of the scope?
Lew, you probably are aware of this, but that miscollimation is almost certainly due to the deterioration of the foam pad that sits behind the primary and holds it in place against its retaining ring. My 1992-vintage Astroscan recently went out of collimation, and I used a piece of 1/2" charcoal-type camera case foam, cut to fit, to replace the old foam.This entailed the removal and replacement of the mirror; I'd done this before, but it's never a pleasant experience, and involves much frustration and accompanying colorful language The result, however, was a perfectly aligned mirror.
If one doesn't wish to go through all that, there's an easier fix for a sagging mirror: get hold of some of that camera case foam, and julienne-cut it into small strips, of a size that can fit through the screw hole on the bottom of the sphere... this should be done with the scope standing on end, so that the mirror is pulled by gravity into alignment against the ring that aligns and captivates it. This requires a bit of time and patience, but once enough of the little strips are up inside there, behind the mirror, they'll hold it in place. This won't be quite as stable as having a solid disc of foam inside, but it does work, and is nowhere near as nerve-fraying as the only other alternative.
It's also a good idea to add safety wires to the diagonal mirror and its support on these scopes; the glue used to hold them in place is getting pretty old. See this CN thread for information on using such safety wires; the pertinent section appears near the middle of the page.
Posted 03 July 2013 - 10:40 AM
Posted 03 July 2013 - 01:36 PM
A Big Thank you , Oh most enlightened one.
Tom, Nice pics
Posted 03 July 2013 - 02:27 PM
I also have one of the old Edmund small-aperture Barlow lenses that was in your scope's eyepiece tube, Tom... as the photo below shows, it was in a cell that fit into an eyepiece tube. If used in a focuser tube, it would require one of the phenolic split rings shown to be placed around the cell. Due to the steep light cone that the Astroscan presents, this isn't the best Barlow lens to use with it; one with a clear aperture approaching 20mm or greater would perform better.
Posted 03 July 2013 - 02:37 PM
These pads are about 4" in diameter, just a little smaller around than the mirror itself, and 1/2" thick when new; the one shown has both compressed and deteriorated. The side view of the pad (propped up by a lime that was pressed into service ) shows approximately how much space is behind that mirror, in terms of both volume and shape.
Posted 03 July 2013 - 04:15 PM
Wonder if that base has been repainted; Eric, does that color match the grey base you have? It looks too silvery to me.
I would say so along with thorough sanding to remove the rough casting. It almost appears as if the cast contact spots were sanded down as well.