Was du glaubst, ist relativ irrelevant 
Ich hatte mal einen Billig-Refraktor (70/900 oder so - ist schon über ein Jahrzehnt her, genau weiß ich es nicht mehr, irgendso ein recht langer Refraktor war es) am künstlichen Stern gehabt, der überraschenderweise grottenschlecht war – bis wir spaßeshalber das mitgelieferte Amici-Prisma mit dem kleinen Durchlass eingesetzt hatten, dann war er richtig brauchbar.
Aber das war auch kein Gerät, an das man eine Kamera anschließen wollte. Bei modernen, auf Foto ausgelegten Apos macht es Sinn, dass sie ohne den Glasweg eines Prismas ein gutes Bild liefern, wenn eine Kamera im geraden Strahlengang angeschlossen ist. Je älter das Teleskop, desto größer ist wohl die Chance, dass es für ein Prisma ausgelegt war.
Beste Grüße,
Alex
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Hallo Alex,
was du im zweiten Absatz schreibst, ist das die Antwort auf meine Frage? Sind die Teleskope auf Verwendung ohne Prisma optimiert? oder eine Annahme, der du mehr Relevanz als meinen Annahmen beimisst?
Gruß
Stephan
Danke für den Link, ich glaube den hatte ich schon mal gelesen, da kam nix klares raus. Oder doch, bei nochmaligem Lesen und zwar so klar, dass ichs hier zitieren muss
Diesen Report hatte ich verdrängt, weil er meine Hoffnung, mein teurer Zenitspiegel müsste gut sein, nicht bestätigte
"After completing observations of Jupiter in the Celestron 80mm APO with the prisms, the various aluminum, silver, and dielectric mirror diagonals were tested. First impression when moving from observing with the prisms to the mirrors was, "wow...more scatter!" I felt this was a rather obvious tell. I was also surprised that the details on Jupiter were definitely softer through the mirror diagonals than they were when using the prism diagonals. As example, the NNTB was not showing though the mirror diagonals, and any structure within NEB and SEB was only hinted at as a nondescript albedo differences. Changing out the mirror diagonals to prism diagonals, and all the NEB and SEB crisp definition and structure reappeared, as well as the ethereal NNTB.
As more and more field observations were conducted with the 80mm APO on Jupiter, it became apparent that the prisms were providing another level of performance that the mirrors were not. While the mirrors were not providing as good planetary views, two of the mirror diagonals were showing some unique distinctiveness apart from the other mirror diagonals. Whenever the Astro-Physics MaxBright was used, it was noticeable that its level of scatter was less than the other mirrors, excepting perhaps the VERNONscope which seemed on-par with the Astro-Physics. So the Astro-Physics Dielectric and VERNONscope Enhanced Silver were generally showing a scatter level between that of the prisms and the other mirrored diagonals. The VERNONscope further distinguished itself as showing nearly, but not quite, the same level of detail and contrast on Jupiter as did the prism diagonals. As field observations progressed, the VERNONscope more and more distinguished itself as having a unique quality to its view and providing razor-sharp planetary views nearly as good, if not as good as the prisms.
Moving from the fast f/6.25 focal ratio APO to the more moderate f/8 focal ratio of the TSA-102, the chromatic aberration tests were again repeated using the bright lunar limb. With the TSA-102, no chromatic aberration could be induced using the prisms on any target at any magnification when viewing the lunar limb. Similarly, when observing bright stars like Sirius, no chromatic aberration was observed at any magnification whether the star was in-focus or out-of-focus. Only when a bright star was racked so far out of focus at high magnification that the star's diffraction pattern was almost 3/4 the size of the apparent field of view did the slightest hints of color begin to appear. And when these slight colors did appear, they were only as a slight blue-black hue to the dark spaces between the diffraction rings. While most manufacturer's seem to advertise f/7 or slower as a focal ratio for optimum prism performance, based on the observations of this comparison I feel that f/6 would also be perfectly adequate as very little color was generated even at this focal ratio. And at f/8, observations showed no negative impacts regardless of the magnification using a prism vs. a mirror, and an clear advantage for planetary observing. These results are similar to those reported by others who have done planetary comparisons for prism vs. mirror diagonals. Examples include:
° Simulations and seasoned observational experience show a prism can be preferred as a diagonal in moderate focal ratio telescopes: Indeed. a prism will add its own aberration (overcorrected spherical and color), but until you raytrace a system with a prism (I have – with ZEMAX), your just guessing at the aberrational residuals. I own a 2" multi-coated prism (Badder Planetarium) and at f/9, it works superbly. With 99% transmission, and the lack of light scatter, this diagonal beats any mirror diagonal I've ever used. Of course, a well made prism will cost more, but until interference coated supersmooth diagonals are available, the high quality prism for moderate to long focal length refractors will reign supreme. … In an achromatic or apochromatic lens, the variations of spherochromatic aberration and secondary and tertiary color make the use of a prism very interesting indeed. Raytracing in ZEMAX -- various APO designs with 25mm and 50mm prisms with f/ratio's of f/6 to f/12 -- shows that the OPD spherical levels for different wavelengths change in different amounts, sometimes improving a system at some wavelength at the cost of others. The ONLY way to know what is really happening is to know the exact design, raytrace the total system, or star test the system, and check to see if the contrast is higher with the prism, or the mirror diagonal. But even with these spherical and color variations, the aberration levels do get excessive at around f/7 or f/8. (Ref: groups.google on 12/1996, Thomas Back, Subj: Prism Diagonals Pros & Cons)
° Simulations support the observations that at f/8, any color or spherical aberration that might be induced by a prism should be non-detectable: If you do use a prism, the small 1.25" won't make a difference that you can see or measure. The 2" will introduce a very small amount of color and spherical, but again it probably won't be visible under normal circumstances. I don't think it will hurt planetary performance at all. I just did a simulation in ATMOS lens design on a perfectly corrected lens. The spherical correction with 50mm of prism inserted into the optical path changes by only 1/40 wave. The color correction changes only minutely to the point where you cannot see any difference at all in the focused star image. I did the simulation at F8. (Ref: Astromart Forums on 2/2005, Roland Christen, Subj: Prism vs mirror diagonal in APQ's - Msg: 306947, 306950, 307121)
° Refractive surfaces produce less scatter than reflective surfaces given a same surface smoothness: “A surface irregularity on a refracting surface produces a much smaller wavefront error than on a reflecting surface, by something like a factor of six "
Die Erfahrung habe ich immer wieder gemacht, in Übersee. Da ist man nicht so verbohrt und von Halbwissen überzeugt. Und eher geneigt, eine von diesem Halbwissen abweichende Meinung wertzuschätzen als deren Vertreter als dumm darzustellen.
Gruß
Stephan
