Friends call me Duane. Compustar C14, Leo Henzl's Custom C8, 6" Refractor Adv. GT mount, 6" F5 Omni XLT Newt., LXD-75 F4 Imaging SN8, Meade 8" F6 Newtonian, EX Dynamax DX6, RV-6 ETX-90 Astro, Meade 2045 4" SCT, B&L 4000 Vixen/Celestron 80mm F11 JC Penny 60mm AZ/ALT Refractor Binos 25x100
Astronomy educator/Sidewalk astronomer
Owner of Astronomy Delight franchise
18 inch f4.42 Dob on eq platform w ST120 f/5 finder
12 inch Zhumell Dob
8 inch f/6.9 home made Dob with Seevers optics
William Optics red 10th Anniversary 80mm FD
C8 XLT on Vixen GPDX
26lb eyepiece box
Cernan Space Center astronomer
Member of Northwest Suburban Astronomers
- Jared Willson
Money can't buy happiness, but it sure makes living with misery a lot easier!
Quote:Secondary obstruction! HOLY COW!! How can that thing have enough clear aperture to have any contrast at all?IS THIS SCOPE mostly aimed at the AP crowd?Does anybody have one of them yet for a review?
Uncle Rod Uncle Rod's Astroblog: http://uncle-rods.blogspot.com/
Celestron CPC Deluxe HD 1100
Sky-Watcher Pro 120ED
Explore Scientific 82° 30mm, 18mm, 11mm, 6.7mm, 4.7mm
Canon T3i Baader mod, Hyperstar, IS-618CIU Camera
My Astro Gallery
Quote:When low power was used that's when the CO was apparent the sky was not as black as it could have been.
Quote:Quote:When low power was used that's when the CO was apparent the sky was not as black as it could have been. This was due to the larger exit pupil, which delivers an image of higher surface brightness.As I pointed out earlier, a large obstruction affects contrast at very small scale, of order an arcsecond. It *does not* cause a brighter sky, in the way widely scattered light can, such effect being called veiling glare.Again, I'm astonished at the vast ocean of confusion out there in amateur land, as regards even the fundamentals of contrast transfer in optical instruments. I really wish the community as a whole would finally get these matters straight, and not propagate the same old misinformation generation after generation.
Orange Tube C8, Tasco 7te-5, 4" Criterion Dynascope, Jason/Towa 313
Nikon Action Extreme & Pentax WPii Binoculars
At my club, everything one could want up to 18"
Quote:What do you mean when you say "spread over the full image"?
http://www.astrobin.com/users/budman1961/ Meade LX3 8" OTA/IEQ45 Mallincam HyperPlus Color, QHY5L-II Mono Orion Mini Finder/Guider
Quote:So if the CO makes no difference, why do Compound Camera lenses never have the contrast levels of a similar sized non obstructed one?I'm just having difficulty grasping the concept, I had read in S&T that the larger secondary has a thicker diffraction ring, that gets spread across the entire image that decreases contrast on a scale determined by the % of the obstruction?Also why is it always such a big topic over in the Refractor Threads?
150mm MCT f/13, 31% CO
"People say I'm in denial. I disagree."
Quote:Looks like it's about a 42% or so obstruction.
David Cotterell Toronto, Ontario "If an observer actually sees an object, there is no point in referring to a formula to find out whether he ought to see it; and if he fails to detect it, no formula will ensure his success." - W.H. Steavenson 8" f/15.5 TEC Maksutov 16" f/5 Teeter/Zambuto Dob 66mm WO SD AT 65EDQ APO Refractor Astro-Physics Mach 1 GTO Mount iOptron ZEQ25 mount Canon 60Da
Quote:Based on the temperature of all the responses to any new Meade thread, why did you ask the question? Not to call you anything, or infer anything, but it seems to me these Meade threads all end up the same way......
Quote:Something about apparent brightness versus percent central obstruction?
Quote: a little contrast loss is nothing a little more aperture cannot cure
Quote:Again, I'm astonished at the vast ocean of confusion out there in amateur land, as regards even the fundamentals of contrast transfer in optical instruments. I really wish the community as a whole would finally get these matters straight, and not propagate the same old misinformation generation after generation.
Quote:Quote:Again, I'm astonished at the vast ocean of confusion out there in amateur land, as regards even the fundamentals of contrast transfer in optical instruments. I really wish the community as a whole would finally get these matters straight, and not propagate the same old misinformation generation after generation. I'm SO GLAD you posted that! There are, indeed, way too many iron-clad "truths" that are no more than uninformed "beliefs"!Unfortunately, trying to 'set the record straight' on these forums only leads to flame-wars launched by the Luddites who just will not listen to anything that disturbs their firmly-entrenched worldview.Wouldn't it be great if someone with widespread credibility wrote a book correcting these misconceptions?Mike
Telescopes: Celestron 14" SCT..Meade 10" ACF/SCT..Stellarvue 4" ED APO Mounts: UA UniStar Deluxe duel clamping saddle on a Celestron CGE tripod...UA UniStar Deluxe on a Meade field tripod and a UA UniStar Light on a UA light surveyor tripod. All with custom made "Manny Miles" eyepiece trays. Binoculars: Garrett Optical 10x50 Oberwerk 15x60. Eyepieces: TV Naglers, and Plossl's. Also Pentax 20XW, a Baader 31 Aspheric and a TMB 40 Paragon.