Orion XT12i with Swayze-refigured primary & Protostar secondary
Televue NP101 refractor
William Optics Megrez 90 refractor
Universal Astronomics Deluxe Mounts
My eyepieces are made from the waste product of exploding stars.
10XTi 102XLT ST80A(2" Focuser); President, Eypieces Anonymous, Denver Chapter (Hello, I'm an eyepiece junky, what's your excuse?)
DAS Dark Site
Active instruments: 4.25" f/6 Newtonian on altazimuth Springfield mount with crutch tripod -- telescope for the handicapped. 12" f/6 Newtonian Telescope maker since 1958; always more to come? Well maybe just one more and it will be something very special Stellafane Awards: 1977 1st award for 4" f/6 refractor 1978 1st award for 4" f/4 Lurie Aplanat 1983 1st award for Newtonian smoking pipe For Sky and Telescope articles, please see Bio info.
Orion ED80 - AT Voyager with TNT,pier ext.,Vixon steel tray and Manny's mod.
Omni 120 cg4 with Orion pier ext. and RA drive, Binotron-27 (25mm & 17mm Sterlings)
Orion XT10(Original F/5) SkyStopper Equatorial Platform
Jason Constellation Model 311(Modified with 1.25"Crawford Machine focuser & rings)
Quote:MY QUESTION IS THIS: Why cannot reflectors be made such that once collimated, they generally hold good collimation indefinitely, similar to refractors?
Equatorial Newtonians, 20" and 14" "The purpose of life is to be defeated by ever greater things." - Rielke
Quote:Why cannot reflectors be made such that once collimated, they generally hold good collimation indefinitely, similar to refractors?
Dan Orion XT8g If your dob isn't broke, fix it anyway. Don't tell me what I want to hear, tell me the truth.
Quote:Folks have developed an aversion to anything that has the possibility of image degradation no matter how small that degradation is. Hence spider assemblies are as thin as possible and although useable, aren't exactly ridgid. Nobody is willing to accept a truly robust spider/secondary support with negative impact to the views.dan
nOOb with a ETX-80, ETX-90 and a Coulter Compact Odyssey 10.
Quote: Quote:Why cannot reflectors be made such that once collimated, they generally hold good collimation indefinitely, similar to refractors? Actually, they can be and indeed are made. I've owned two of them - both Orion 8" f/6. I check collimation but unless I monkey with the mirrors or focuser I never have to tweak it.
Uncle Rod Uncle Rod's Astroblog: http://uncle-rods.blogspot.com/
Quote:The other side is that a Newtonian that must be collimated is simple to make. AND collimation is a five minute process at worst unless you are a collimatoholic.
Quote:I am no expert, but I believe as this thread develops it will be found that the inability of the secondary holder to hold position to within the extreme tolerances necessary to achieve perpetual collimation will be the weak link. Eric
Quote:rather the angle I'm interested in is why hasn't it seemed feasible (at least so far) to improve the overall structural design of reflectors to mostly eliminate their vulnerability to miscollimation for an indefinite duration, once it's been initially set?
Scopes & Stuff:
16" F5 Teeter/zambutoTom Osypowski equatorial platform10" F5 LightbridgeMid 70's RV-6Orion 100mm EDATMing:Low Profile Front Collimating Dob/Cell for 16" Conical MirrorFront Collimating Dob/Cell for 16" Standard MirrorDob Driver with novel azimuth friction clutch, and axial (rotating) electrical connection.Red Oak Observing PlatformRed Oak Combination Observing Chair (Post Pending!)
Quote:If I scaled the 4" refractor here up to the 12.5" size, my scope would weigh around 300+ lbs because the entire structure would have to be beefed up to handle the weight of the tube, etc.
Quote:Question: ( I know absolutely nothing about this one) How often is a large professional observatory scope aligned? Do they check it for every exposure? Is it remotely adjusted so that continuous adjustments are possible? Or is it ridgid enough that collimation can be set and left?dan