-DannyMy warehouseMy Channel
Webster/Zambuto 14.5" f/4.3 truss dob
Tele Vue-102, Gibralter mount
Tele Vue-76, Tele Pod mount
Canon 10x30 & 15x50 IS binocs
Jeff -----TEC 140, Stellarvue SVR90T, SV115T20 and AT65EDQ refractors,Webster D14, C11 EdgeHD Lunt LS60THa solar scope double stacked with LS60FHaTelevue Pan 41; Ethos 21, 17; Nagler 31T5, 9T6, 7T6, 5T6, 3.5T6; Delos 10, 12, ES25, 14, 9Astro-Physics 900GTO with Rob Miller Tri36M TripodDM-4 Mount-Extension-Tripod w/ Sky CommanderDM-6 Mount-Losmandy Adapter/Extension-Berlebach Planet w/ Argo Navis
Quote:An f/3 (f/3.5 with Paracorr) scope would force me to totally rethink my eyepieces. My Ethos 21mm would would have an exit pupil of 5.99. I would be limited to Ethos 17mm for matching my pupil dilation and typically limited to 7mm or longer do to typical seeing.
10" Sumerian, Webster D18, solar scope, small 'frac, Vixen Foresta 8x42 Take action against Light Pollution. Together we can make a difference.
Quote:Quote:An f/3 (f/3.5 with Paracorr) scope would force me to totally rethink my eyepieces. My Ethos 21mm would would have an exit pupil of 5.99. I would be limited to Ethos 17mm for matching my pupil dilation and typically limited to 7mm or longer do to typical seeing. If the exit pupil is a little larger than your own pupil it really is no big deal at all. No reason that I can see to avoid using the 21 mm Ethos on such a scope.
A 60mm department store refractor started it all....
Quote: Put a Wynn 3" corrector in a 3" focuser, and a 17 E in it an it would make some sense...
Quote:It will perform just like a 16 F4.5 with a 31 Nagler in it... Way too much wasted light.... as you say with a smaller EP, you wont waste, light on the exit pupil,
Quote: ... your looking at least a 6" secondary not to vignette terribly, and now you are back to 25 percent CO. Compared to 14% in my 25 F5 so contrast should suffer over a traditional dob.
Celestron 8SE Dobstuff 13.1": Swayze refigured Coulter mirror, 6 pt mirror cell (2 pt edge support) and CF focuser board made by me StarBlast 4.5 ST80/PortaMount II Zhumell 20x80/Oberwerk 15x70 on a Seronik-style tripod boom mount Hubble Optics 18 inch F/4 mirror.
Rob 18" f/4.3 Starmaster 8" Meade LX200 Classic Celestron 15x70 Skymaster Binoculars
Quote:Shipping it with a 2" focuser shows they don't understand light cones.....
Quote:Put a Wynn 3" corrector in a 3" focuser, and a 17 E in it an it would make some sense...
Quote:Other than that its a scope for someone with lots of money that doesn't understand optics, Exit Pupil, and vignetting.
Quote:Lets look at illumination for a second... the 21 Ethos has a 36mm field stop. At F3, I would guess your edges are at best 60% illuminated.... the drop off at F3 is tough.
Quote:I havent even checked Newt to see if the upper cage vignettes at that fast
28" Webster/Lockwood f/2.75 - eyepiece height 70"
Florida 27° 15' N
Quote:Look at Mike Lockwoods, own website, for secondary illuminations. Your figures unless you have around a 7+" secondary are not possible. 7" Secondary is 25% CO....If you are getting 0.4" at the SIPS, what happens in the distance between the SIPS field lens and the Eyepiece field lens? Answer The light cone drops as a function of distance between is what happens. If you have 1.5" or so between the SIPS exit lens and the field lens of the 21E you actually have well, 0 fully illuminated. Hence the need for the Wynn and a 3 inch focuser, and an even Bigger Secondary. There is at least one person who uses it visually and that I believe was posted here a while ago.
Quote:I take it you also havent read the recent post on Paracorr 2 performance at F2.8 in Mikes group? check it out makes for a good read.....
Mike Lockwood - Owner, Lockwood Custom Optics. 20" F/3 MX Starmaster, 14.5" F/2.55 self-built Newt., nine self-built scopes, 4.25" to 30" http://www.Loptics.com/
Quote:If you are getting 0.4" at the SIPS, what happens in the distance between the SIPS field lens and the Eyepiece field lens? Answer The light cone drops as a function of distance between is what happens. If you have 1.5" or so between the SIPS exit lens and the field lens of the 21E you actually have well, 0 fully illuminated.
Quote: Lastly this also doesnt account for the SIPS' other shortcomming which is that it can be optimized for the distance from the EP to focuser, like a normal Paracorr 2 (over that range the SIPS effectiveness would vary significantly)
Quote: If you let me know your secondary size, cage ID, I would be interested in running the numbers.
Quote: I take it you also havent read the recent post on Paracorr 2 performance at F2.8 in Mikes group? check it out makes for a good read.....
Quote: Why do they make 3 and 4 inch focusers and Wynn correctors? To illuminate a full frame 35 Millimeter chip without clipping in the focuser.... How big is a 35MM chip compared to a 21 E Field lens?
Quote:Mike at F3 you say the sips has a fully illuminated spot of 13 MM at the focal plane (which is what i think you are saying), I agree with you IF the field lens of the SIPS is fully 100% illuminated. This would require a MONSTER Secondary to accomplish.
Quote:In The adjustable 20-40MM distance the light cone is still doing its thing (e.g. coning, so 13MM would like correspond to the 20MM side of the adjustment, less so at the 40mm side), What I am trying to get at is that the focal distance of various ethos eyepieces require over a 1" movement of the eyepiece relative to the focal plane, the light cone is again their coning.....
Quote:So, we calculate illumination based on the focal plane location without the SIPS. I measured my Paracorr 2 lens (can't get to my SIPS right now) opening at 42mm. At f/3, a 29mm diameter light cone will focus 88mm from the bottom of the SIPS. This is obviously smaller than the 42mm lens, so the central spot is easily fully illuminated at f/3.
Meade 16" f/4.5 Lightbridge M42 w/Paracorr & "Crossbow" EQT-200 Equatorial Platform
Meade AR-6 w/10:1 Dual Speed Crayford Focuser
Meade ETX-125 Terabeam/Wegat
Orion ST80 w/single speed Crayford Focuser
CGEM Hypertuned by Deep Space Products
Quote:Heres how I might play with it..... Extend the cage forward a bit, and give a little more backfocus. As it sits I am going to get alot of light from above the cage on the field lens of the Eyepiece.... and If I put a flockboard up the scope will again vignette. so backing out the focal plane with a 3" focuser and a paracorr 2 is imho a better solution....
Quote:Here are the results, perhaps I got a parameter wrong but he scope vignettes at the secondary cage. The focuser to front of tube distance is also likely short.
Quote:all of this put together is at F3, I do not beleive an Ethos 8 would have any areas 100% illuminated, even with a fully illuminated SIPS....