As I wrote in my earlier post, I picked up a vintage Criterion 4-inch Dynascope reflector this summer in Quebec City. I got it from a gentleman whose late father was an educator, and rescued it from a school when it was marked for disposal.
There is no model or serial number information, but as near as I can tell, it's a 4" deluxe Dynascope, with the 1.25" focuser, and made from some sort of resin-impregnated cardboard. I have it on a quite usable GEM, with some nice clamping tube rings, but the fixed bolt on the tube tells me this was originally mounted on the older-style EQ mount without the tube rings. I have read all of the threads on CN I can, and have had a look through various era catalogue ads, and I still can't tell when this might have been made. I'll call it "1960s" and leave it at that
Since then, I've:
- disassembled, cleaned, and regreased the focuser mechanism and finderscope focusing threads. The brass focuser is a bit tired with age.
- removed the primary mirror cell with a rubber strap wrench. Unfortunately, a previous owner has already attempted a cleaning, and as a result some fairly deep scratches are present, which I don't think can be addressed by a simple recoating. I carefully cleaned away the dirt and haze, and will just live with the scratches.
- added teflon washers to both axes of the mount, which are an improvement over the half-century-old nylon ones, and added a small c-clamp to firm up the latitude adjustment a bit. Things are pretty smooth and sturdy now, though we're still upset a bit by the odd strong gust of wind. I also need to find properly-sized teflon washers.
- added a red-dot finder (temporarily zip-tied to the tube, as I don't want to make any permanent modifications yet. I find the combination of a magnifying finderscope and an RDF to be useful a useful one, especially in city skies when I don't have as many guide stars to use for hopping.
- shimmed the focuser with some black craft foam to centre things as well as I can using an Orion collimation cap. Initially, it was WELL off. I realise this isn't ideal with the much-maligned secondary mirror, but it's where things are going to be until I can get a hold of a spare focuser/secondary mirror assembly to modify. Just looking at the back collimation screws, I can see there's probably a slight tilt in the primary.
Performance, I think, is as good as it's going to get for the moment. My only other scope is a 100mm Orion Skyscanner, which is dead-simple to use, is super-portable, and gets me good wide-field views. At f/11.5 vs f/4, I think the Dynascope can give a crisper image in most circumstances, and is certainly easier to get up into the 100x + magnification range comfortably. The 10mm and 20mm plossls that came with my Orion Skyscanner do pretty well on the Dynascope: better than the supplied Criterion H18, AR9, and AR7. Between those two eyepieces, a 2x barlow, and a 40mm MA, I've been able to bag the Messier objects I've hunted for so far, and gotten some lucky glimpses of planetary detail in the late summer when Jupiter, Saturn, and Mars were "doing their thing" higher up in the night sky.
Star-testing collimation is a bit weird with the square focuser, and also occasionally puzzlingly "off." I was stumped for a good while, until I realised that 1) the lack of any mechanism to tighten around the eyepieces meant that at certain angles and elevations, the wiggle-room in the focuser led to a misaligned eyepiece, and 2) the long, long tube takes more time to acclimatize than I'd expected!
Edited by ktran, 29 October 2018 - 05:58 PM.