Quote:If it was April 1st again I might have the courage to goto the refractor forum and start a "Does your refractor give reflector like images?" thread.
Quote:But assuming the best possible newtonian optics - excellent substrate surface, clean, and highest quality coating - do this:Buy a large dob, say 16+ inches, with premium optics. Build a 6 inch off-axis mask, and knock yourself out enjoying extra-diffraction-free (Mak-Newt like? ) views of planets and bright stars when the mood hits you. And when you've had enough, crank up the aperture and resolution and do some serious observing!Joe
Scopes: 10" dob Antares Optics 1/30 wave secondary/Moonlite CR2, 13.1" home made truss dob Discovery optics, 4" achro (the banger)
Quote:Hmmmm, sorry, my experience has been no. My "big" refractor is a 6" f/8 achro while my reflector cut a broad swath from 4.5" f/4 to 16.5" f/6.5, Newtonians, MCTs, and SCTs. The image through the unobstructed refractor is just so darned clean. You can also easily max-out the exit pupil without having to dodge around the shadow of the secondary. I luv my reflectors, but my biggo refractor is a special piece o'kit.
Happy owner of-- A Mag 1, 12.5 inch Porta Ball A Dual Axis Equatorial Platform A PST Double Stack
Quote:Quote:If it was April 1st again I might have the courage to goto the refractor forum and start a "Does your refractor give reflector like images?" thread. Do it!
Quote:Funny how people who have nothing in there lives perfect sure worry about the stars to be perfect.Bet most do not get there eyes checked or blood presure. but the stars need to be sharp . Guess I am one of those .Ha Ha
Quote:If I have a lot of time I like to setup both a refractor and my 10 inch dob. Dob for DSOs (and planets when seeing is good)...and refractors for wide fields and planets.
Orion XT12i with Swayze-refigured primary/Protostar secondary
Televue NP101 refractor
William Optics Megrez 90 refractor
Universal Astronomics Deluxe Mounts
Celestron C11+EQ6, skywatcher /Zambuto 12"dob,watchhouse tracking platform, 16"/Zambuto lightbridge , Ethos's 6,8,10,13,17,21. Naglers 31,26. Lieca ash zoom, televue 2.5 powermate,2"2x powermate .Paracorr type2. Howie glatter 2" laser & Tublug. Lumicon 2" UHC, 03, H-Beta,Televue smoothies ( all of em) , Meade 4000 smoothies ( all of em). That'll do for now.
Quote:But then there's thermal issues. At worst the column of air in front of the mirror is a defocusing lens the refractor camp doesn't have issue with to the same degree to say nothing of the sheer thickness of them. I'd place thermals as a close second behind large CO contrast degredation.Its almost silly when you consider the thermal issues a reflector has to endure...Imagine an apo where an observing buddy is breathing on the side of your dewshield every time you look in the ocular. That's no different than what happens at the reflector focuser when observing.Imagine you have a push-to refractor and every time you need to shift it you reach up with your hand on the dew shield edge to nudge it with all the thermals pouring off that - something I think we've all seen with reflectors - particularly in out if focus stars on collimating.Then there's the length of a dew shade on an apo compared to the length of a truss or closed tube. It's simply more room to further create the lensing effect of this warmer air.The sheer thickness of the glass is what Gary Seronik refrs to has the effect of having a heat battery. Even a very large apo at least has the glass in thinner sections*.Anyway, having dealt with and been (finally) successful for the most part dealing with the defocusing effects of thermals Im a true believer in it being one if the serious potential detriments to reflecting systems when left unabated.Pete*theres been mention apos over 7" have very long cool down issues but this doesn't seem like it has to be if there is air between the objective elements why not a cell that blows air through these spaces and be done with it. A reflector should only have such an easy option.
Quote:My 12.5" always beats the 5" and 6" apos in the field, but that's not really a fair comparison. Alas, I have no 10-12" apo refractors handy to compare to it. But, for the price of my high-end 12.5" f/5 with Zambuto mirror, I could have bought a nice 4" apo on a cheap mount.
Tom Karpf (tkarpf) Vice President, Astronomical Society of Greater Hartford www.asgh.org
Selsi 60mm f/13 Lunt 35mm Solar Scope Stellarvue SVR70ED
Astronomy Technologies AT6RC Home-built Dobsonian with home-made mirror -
8" f/6.8 Unistar Deluxe on a surveyor's tripod
Quote:Quote:If it was April 1st again I might have the courage to goto the refractor forum and start a "Does your refractor give reflector like images?" thread.
You would have probably gotten a Moderator Alert for stirring up trouble.
1st Caveman Award!Maynard Clark 8" f/8The Horsetrail Cave 12.5" f/7.51975 Cave 8" f/7 Lightweight Deluxe1972 Cave 8" f/4.5 RFT DeluxeCriterion RV-6Logitech HD C615 Webcam for Imaging
Quote:I think one thing that is often overlooked is comparing apples to apples quality levels between reflectors and refractors. For instance, a lot of people seem to compare a 4 inch Televue or other top end company to an Orion 10 inch dob. I'm not saying there is anything wrong with an Orion 10 inch dob (love mine), but it's not a high end dobsonian. A better comparision would be a dob which has been optimized design wise and has a high quality mirror. You could even compare those in terms of cost. A high end 10 inch dob can cost as much as a high end 4 inch apo.
People really should look through as many scopes and designs as they can to appreciate what type of scope they would like. A friend of mine has a Maksutov Newtonian which provides absolutely awesome views.
Joseph Cannavo FrontCollimation 16" F5 Teeter Dob Driver with novel azimuth friction clutch, and axial (rotating) electrical connection. Tom Osypowski equatorial platform 10" F5 Lightbridge Mid 70's RV-6 4" Orion 100mm ED Mr Keeyoots (My Cat).
Quote:I think one thing that is often overlooked is comparing apples to apples quality levels between reflectors and refractors.
Money can't buy happiness, but it sure makes living with misery a lot easier!
Quote:I am curious on this topic as I sometimes see that claim by scope makers. I am especially curious as to honest opinions regarding the <f/4 large dobs. We all know you get a brighter image and can see more, but does anyone feel that you get as crisp an image as an APO?
Quote:Nah, 12.5" will ALWAYS show more.
Quote:Quote:I think one thing that is often overlooked is comparing apples to apples quality levels between reflectors and refractors.
Very common. I always question when someone wants to compare a basically handcrafted refractor to an off the shelf Newt or SC and do it in an apples to apples context. And 9 times out of 10, it's comparing planetary views. That's fine if all you do is look at Jupiter and Saturn and the Moon, but that 10" off the shelf Newt is a big winner when you compare it to a 4" top shelf refractor when looking at NGC891.
Quote: The image through the unobstructed refractor is just so darned clean. You can also easily max-out the exit pupil without having to dodge around the shadow of the secondary.
Quote:Quote:Nah, 12.5" will ALWAYS show more. Oh really, how about Collinder 70 Don.
Quote: NP 101 was made for guys with large reflectors. It is the perfect companion to a large reflector.
"I have been paddling in the shallows of a great ocean of knowledge." - Sir Isaac Newton * * 15" F4.55 Starsplitter Dob & a Denk II binoviewer * * http://peaceofsky.wordpress.com/ Pacheco State Park Fremont Peak