What is the definition of a Petzval? (I think as originally designed by Petzval the front and rear each have to be 2 lens elements, right?) Number of lens...
You can't take away the rear group of lenses from a Petzval telescope and still get a good image from the front group alone. That seems to be the difference...
... Petzval have one advantage over an apo and that is the reduction of field curvature thanks to the permanently installed field flattener, but for visual...
... A lot of field curvature is very much visible visually in two high end apos I have but not in a third by a different mfr. I even asked if a field flattener...
... Field curvature is directly related to the focal length of your apo, being high end has nothing to do with that. Is your third scope with less curvature a...
OK, let me re-ask my question this way: What is the difference between the rear element of a Petzval and a field flattener? I am interested in what it is that...
My first order comment (Roland's will be definitive) is simply that Petzvals allow you to reduce focal ratio down to the neighborhood of 5.0 to 5.5 and still...
If I have to guess the field flattener on an apo is situated very close to the focal plane and has minimal or no effect on the F ratio of the system. In a...
... There are many ways to build a flat field optical system. A traditional Petzval is one way. Basically it is two achromats with an airspace between them....
So a Petzval, rather than being a "special case of a refractor + built in flattener" is a "special case of a refractor + built in reducer/flattener". Is that...
Seems to be, as the short refractors have that cursed field curvature so bad for AP, but short scopes are what you want for widefield. I think the design was...
A Petzval telescope is a spcial case of a dialytic telescope, a dialytic telescope being a telescope with widely separated lens elements. A Petzal really is a...
... Unless you use special ED glasses a Petzval does not reduce chromatic aberration. It still has the same CA as any achromat, however because the front...
... Yes, I know. Just mentioned it anyway. I have one TEC at f/7 and one TEC at f/8 which have similarly obvious FC and one Tak at f/8 with seemingly very...
... Actually, Newport Glass has an air-spaced f/15 BK7/F4 doublet kit. I tweaked that design to make the inner RoCs mate -- not a huge change to the overall...
... Here is a follow-up question based on the example of a Petzval achromatic refractor with a F/10 doublet (say with an aperture of 5") up front and a 0.5...
... I recall an ad in S&T by Roland, looooong time ago, where he offered a Zeiss AS 8" F/15 objective for sale, I believe for about 5K, but the interesting...
... I did make some about 12 years ago when the AS lenses were available. They became F7.5 speed with a length of an 8" F11.3. The rear set used and ED doublet...
So....is it true that if you want to build a fast scope say under f/6 that it is easier/less expensive to do using a four element Petzval design than a triplet...
Three words - coll - i - mation. I think there is good evidence that the best design is a triplet APO with oil spacing. It's this - if there were a better...
How about a Tak FSQ vs an 80ED w/ a FRFF Chuck/divenuts ... From: svfanatic To: Refractors@yahoogroups.com Sent: Monday, March 02, 2009 3:28 AM Subject:...
... When you say faster, do you mean shorter or faster photographically? If shorter, then no, a Petzval is the wrong way. If faster photographically, then...
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