18" f/4.2 homebuilt truss 12.5" f/6 hybrid tube dob
Quote:Over the years I've collimated countless fast reflectors, in the f/4 to f/5 range, using a Cheshire; the caveat being that the mirror must be accurately center-spotted. A final fine-adjustment while star-testing for best diffraction pattern, and... done.This presupposes that the diagonal mirror has been set up properly beforehand, but even if it has not been, it takes but a little longer to set that to rights.Lasers and crosshair collimators can increase the precision of collimation by a miniscule amount, but I feel the ROI (Return On Investment) is vanishingly small, and is in almost all cases subsumed by atmospheric instability and the limitations of the observer's eyesight.As to the OP's question: are you missing ANYTHING? Perhaps, but it is such a vanishingly small anything that you would likely not realize that you were missing it, even if you had seen it in the first instance.
Quote: So where the f/9 scope user can 'eyeball' the primary alignment, the f/4.2 user needs to use a cheshire or barlowed laser to get the primary collimated anywhere near close enough.
Quote:George's reference to a 'cheshire' was probably to one of these combination tools I mention. In some of the high-end tools, the sight tube and cheshire are separated into two tools.
Ed Jones ........... The best data is an interferogram, the best analysis is from an honest optician.
Till now - some 19 years - Ive used simple eye balling alignment with no Cheshire eyepiece, auto collimated, laser or the like. If it looks good through the open draw tube in the focuser, I make sure concentric rings are had on diffraction in out of focus stars and call it a day.
Am I missing anything?
Orion XT12i with Swayze-refigured primary & Protostar secondary
Televue NP101 refractor
William Optics Megrez 90 refractor
Universal Astronomics Deluxe Mounts
Quote:I find it interesting that Parks did not center spot their mirrors, at least mine isn't. They included an eyepiece with their scopes for collimation and their instructions focused on getting everything concentric.Now I'm not suggesting that more advanced tools and techniques aren't worthwhile, I'm studying Vic Menard's book on collimation right now. But it is interesting to me that a company like Parks, who marketed their products as a cut above everyone else, would endorse a method that might not promote optimum clarity.
Quote:...Till now - some 19 years - Ive used simple eye balling alignment with no Cheshire eyepiece, auto collimated, laser or the like. If it looks good through the open draw tube in the focuser, I make sure concentric rings are had on diffraction in out of focus stars and call it a day.Am I missing anything? I like high power when the sky allows it, Galilean moon study etc. could I benefit from a sighting tube for collimating
Quote:This reminds me of a story over 40 years ago, my old friend Stan had a 10 inch Cave and was having trouble getting good alignment using a Cheshire. There were no lasers back then but I had learned a neat way of aligning my 6 inch f/8 and I offered to do his the same way. I would put an 1.25 inch brass tube in the focuser and I would look a foot or more away. I could tell when my eye was aligned with the axis of the tube by the reflections in the tube. I could also see the reflection of my eyeball and found that when my scope was properly aligned I could see my eyeball centered in this tube. I offered to align Stan's scope the same way and afterwards we were looking at a perfect diffraction pattern at 600X or more. He was quite pleased and his Cave had an awesome mirror. After lasers were available I no longer used this method but actually the principle was the same. Guess I'm showing my age.
Jeff Morgan - Wile E. Coyote School of Telescope Making
Quote: When I started working for Scope City, which was owned by the owner of Parks, one of the first things I did was to get Parks to start putting center marks (triangles) on their mirrors. So the later scopes and OTAs DO have center markers.You see, how they did it was with translucent templates, laser reflections, and focuser transparencies, etc. They took a day to collimate each scope.But they failed to allow for the fact that the transport of that scope would knock the scope out of collimation, even if only slightly, and that meant the user could not replicate the factory collimation easily. The center marker on the primary not only shortened the factory collimation to 15 minutes each, but also meant the end customer could also recollimate easily.Their techniques were pioneered back in the f/7-f/12 era, and just hadn't kept up with today's f/4-f/6 standards. They didn't even realize that you couldn't simultaneously collimate a short f/ratio scope and have the shadow of the secondary appear concentric with the primary or focuser.A Parks mirror is definitely worth owning, but the first thing I'd do is to center mark the mirror with either a triangle, donut, or Hotspot.
Quote:I do like the cheshire for the secondary mirror alignment and its crucial when I collimate my bird-jones scope but to each his own.