Quote:Quote:(Apo-)Refractors smaller than 150 mm are very suitable for DSO astrophotography but I don't know how M31 would look like in a 70 mm refractor for visual observing
not very good if anything
Quote:(Apo-)Refractors smaller than 150 mm are very suitable for DSO astrophotography but I don't know how M31 would look like in a 70 mm refractor for visual observing
7x35 and 10x50 sears tower binocs, 3" f/10 edmunds reflector, 2.4" f/11.7 manon refractor, 6" f/8 jaegers refractor, 10" f/11 R30 Istar refractor, 3" f/15.8 sans&streiffe refractor, 3.1" f/15 selsi refractor(towa 339), 2.4" f/15 sears refractor, selsi 30x30mm spyglass, criterion 5-draw 25x45x75x spyglass(1957), 4.25" f/14.8 tasco 20te.http://cleardarksky.com/c/OmahaNEkey.html
Quote:I like to see a comparison with a 12.5" Zambuto Starmaster. Some if not most of these bigger mirrors have zones and turn downed edges.
Quote:But curious as to why you cannot detect any aberrations in the star test in any large mirror?
Quote:Peanut butter jelly. peanut butter jelly time! I look forward to the next blow up and the lock.
Quote: I DO believe a Refractor is the best scope there is.
Quote:OK, no problem. But, #1)I don't think you should say that we or I "should" say anything in particular because this is a refractors forum.And, #2 I have been observing since 1965. I have owned all types of scopes including a 20" Obsession and an 18" Zambuto Starmaster. Both are gone. They were both in a roll-off roof observatory with my 10" TMB F/9 apo, first the 20" then later the 18", and almost never got used. I DO believe a Refractor is the best scope there is. And I am not demeaning any other scope or what anyone else believes. Just speaking for myself.best,JimP
Quote:I find that there is no one best scope...
Quote: Quote: I DO believe a Refractor is the best scope there is. I find that there is no one best scope.A 10 inch f/9 likely ok tor some objects in some situations but the 90 inch focal length makes for a narrow maximum field of view as well as a scope and mount that is difficult to transport and setup. Now if one is lucky enough to live in a black zone with excellent seeing, the manageability is not so important but for those of us who do transport our scopes to darker or more stable skies, there are scopes that are more practical.As refractors grow in size they inherently become longer because color correction scales with focal ratio/aperture so that while a 10 inchNewtonian is a reasonable scope to build, a 10 inch f/5 refractor is notThe best scope, the one I happen to be looking through at the moment.Jon [/quoteHi Jon, I believe I answered in detail in my following post why I feel an apo is the very best scope (for me). You may not agree but then you are not me. :^)The objects I view do not need a wider FOV than it provides. It is a Fantastic telescope and I would not trade it for any other telescope. Period.Jimp
Quote:Even for deep sky observing optical quality matters unless we are viewing wide angle objects at 30x.Proper baffling is important and that is why refractors have an advantage over truss systems or reflective tubes.But large dobs make up for that with lots of aperture.Its amazing what a 10" or larger scope shows.Even in the city Planetary Nebulas look good and OIII and UHC filters can work magic.It would take a world class site to get the full resolution out of a 20" mirror.
Quote:Sounds fantastic JJK. And, of course, when you head out to the Dark Sky site you only take your big dob. That helps. You don't have to decide which scope to use or what type objects to view. I'd love a peak through that 25"! I'm sure it is fantastic!!JimP
Quote:I have a question for all you refractor folks.. what would be the minimum aperture (for a refractor) to do decent DSO viewing?
.... back yard astronomer ================= Don't forget to look at the moon often. Its a play ground of fun if you throttle up the magnification!
Quote:All you really need is a 10" F/11 R30 with a little wide field help from a 6" F/8. Which deals with the photons in a way dobs can't.....sharp and to the point! Mike
Quote: Quote: Aperture doesn't rule, looking up and observing does..... Bravo!Clear skies!Thomas, Denmark
Quote: Aperture doesn't rule, looking up and observing does.....
Quote: We all know that a 1/8 PV surface error is 1/4 wavefront error effectively doubling all abberations and this is just the primary!Now the 1/4th wave hits the secondary and doubles the error again to 1/2 wavefront error.
"You're not afraid of the dark, are you?" - Riddick "The best scientists are humble. They seek to understand, not to ensure their legacy, but merely to understand." - Mori
Quote: Quote: We all know that a 1/8 PV surface error is 1/4 wavefront error effectively doubling all abberations and this is just the primary!Now the 1/4th wave hits the secondary and doubles the error again to 1/2 wavefront error. If the secondary is of a higher accuracy than the wavefront that hits it, then the error of that wavefront won't be doubled, though it will still be affected. If both mirrors are 1/10th wave on the surface, then the final image will be 1/4th wave on the wavefront. That is at least what my logic tells me. Clear skies!Thomas, Denmark
Norme 150mm MCT f/13, 31% CO Yellow Zone "People say I'm in denial. I disagree."
Quote:Sure, 1/8th on the primary surface is 1/4 P-V.
Quote:So more aperture is better but thats for a rabid deep sky fan that has lots of time and money on their hands plus scopes more than 8 or 10 inches dont work very well in light-polluted skies
SLAP Observer --- TMB130SS, SV102V(LOMO Lens), SV80ED Deluxe "The only thing necessary for the triumph of evil is for good men to do nothing." -- Edmund Burke. "People sleep peaceably in their beds at night only because rough men stand ready to do violence on their behalf." -- George Orwell "The measure of a man’s greatness is not determined by what he accomplishes for himself, but by what he accomplishes for others.” -- Some Bald Guy
My eyepieces are made from the waste product of exploding stars. 10XTi 102XLT ST80A(2" Focuser) XW: All; XO: 2.58 Televue: Naglers-T1 Smoothside-full set, 17T4,12T4,Ethos 17,4.7; plossels-40,32,20,17,&7.4mm; Pans-22,24mm; Delos-6,8,12,17.3mm ES100: 5.5,9*,14,20 ES82: full set ES68: 16,20,24,34 NLV: 5,9,10,15 Ortho: HD-7,9; OPS-9,12 Meade RG 7mm Other: Pentax 12.5K(.965), 10mm Parks Zoom: Nag3-6 *=on b/o DAS Dark Site
Quote:wide DSOs benifit from a wide field refractor while faint DSOs benifit from aperture.there is definitely a place for refractor for viewing DSOs
Astronomer for the People. "Taking Chaos out of the Cosmos" "There's an amazing universe all around us...EXPLORE IT!!!" So many galaxies, so little time!