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've done extensive star testing on an 8 inch f3.3 scope for the past several months with and without a Paracorr 2. I've not seen any difference in SA with and without the P2, but there is certainly a small difference among some of my eyepieces.
17.5" Dob "Beta Version"
NP 127 on a CG-5 and CGEM DX
25x100 and assorted other binos
Naglers, Ethos and various others.
Quote: But with respect to definitively settling your question, one problem is that I don't think the optical prescription for the Paracorr is out there. As such I don't know if any spot diagrams are available.
Quote: Otherwise it would mean little to point out (as Al also did) the design SA of certain of the then-new Ethos line - as in around 1/100th wave. Best,Mark
20" homebuilt truss dob 6" watson refractor
Jeff Morgan - Wile E. Coyote School of Telescope Making
Quote:Jeff the only thing that SIPS solved was the ability to focus any ep without having to concern yourself with setting the paracorr to the right setting with each ep used.
Quote:What do you think of this test for the degree of spherical aberration introduced to an optical train by the Paracorr? Test apparatus required:Paracorr, a 250 line/inch Ronchi eyepiece, an accurately-collimated newtonian reflector which is known to be free of significant spherical aberration.Method:1. wait for a near-ideal night and observing conditions with respect to great seeing and minimal scintillation.2. allow the system to achieve, as closely as possible, thermal equilibrium 3. critically examine (or even photograph) the images in the Ronchi eyepiece with and without the Paracorr inserted and look for signs of SA. Would this test be sensitive enough to answer the intent of OP's query? Has anyone tried something like this before? ------C
Homemade 'scopes 8"f/7,6" f/5", 6"f/4, 4.25" Schiefspiegler,60mm Coronagraph,60mm H-alpha system, 4.25" White-light Solar Newtonian,solar spectroscope, 4" f/12, 4.5" f/16 & 6" f/12 Schupmann Medial refractors, 4" Celestar, 19 Stellafane awards 9 in optics Engineering = Taking what you have and making what you need.
Quote:Dave,Very interesting. So the Paracorr adds undercorrection. I wonder if any opticians who KNEW that the mirror was gonna be used with a SIPS in place has ever intentionally added a slight amount of overcorrection as a result.
Quote: Very interesting. So the paracorr adds undercorrection. I wonder if any opticians who KNEW that the mirror was gonna be used with a SIPS in place has ever intentionally added a slight amount of overcorrection as a result.
Quote: The Paracorr adds more then 1/100 of wave error since the top of yellow shaded area on the Televue graphs is the diffraction limited cut off of 1/4 wave and the y-axis is linear. So for each graph one can divide that area up and determine what the scale would be in fractions of a wave. So the Paracorr is adding about 1/10 of wave or more of SA depending on what the f-artio of the mirror it is used on. For example if you look at the curve for the F/3.5 mirror the diffraction limited area starts at just a little under 3 on the graph so that is 1/4 wave and the Paracorr data starts at about 1.3 or so, which would translate into roughly an 1/8 wave of under correction. http://www.televue.com/engine/TV3b_page.asp?id=61&Tab=_con I believe it has been discussed here, a number of years ago, of designing an astrograph using at that time the Paracorr which today is the Type-1 version in which the primary was made hyberbolic to correct for the under correction introduce by the Paracorr. I thought that Televue might have sugguested this as well. The older Type-1 unit added more undercorrection then the new Type-2 units. - Dave
Quote: When the image is larger then the Airy disk it is no longer diffraction limited by definition. So when one has exactly 1/4 wave optics they produce an image in which all the light just fits inside the Airy disk. So this is the upper bounds of the shaded yellow area. So one can relate the theoretical diameter of the spot formed when using a Paracorr which in this case is labeled Airy disk radius to the wave front and estimate the amount of spherical aberration the Paracorr is generating. - Dave
But it is obvious from the graphs the addition will be very small. I can vouch for that, since I DO know how to perform a star test (and I usually see all kinds of aberrations in scopes, the two most common of which are astigmatism and spherical aberration), and the With/Without tests using the Paracorr II display no visible axial changes at all in my f/5 scope.