Originally Posted by harthenry
Hi Stanger --- That is an interesting limb…. I am currently using the French Prisms with the AR (anti-reflective) coating. Although they perform OK, there does seem to be quite a bit of aberration and astigmatism issues. I thought I read in one of Mark’s posts a couple years back that he had much more success with the cylinder lens than the Prisms?
Yeah, it's a complicated subject. What little I understand is you have a bit (quite a bit) more freedom in design with cylindrical/spherical elements than you do with simply prismatic ones. There are things you just need a curve to fix and you can't get that with a prism. But my point was more that it has less to do with the fact that the "main" elements are cylindrical instead of prismatic, than it does the fact that the extra care/time/expense was taken to design all the extra elements.
IIRC the typical DIY lens consists of just two prisms. The limb I was going out on is that an equivalent lens using just two cylindrical elements (I thought I read a post where somebody specified what those had to be, but I can't find it), would have largely the same issues. You need to add the extra elements to correct CA and astigmatism.
Yes, I could purchase the additional lenses for my Prism setup that can be integrate in to help with astigmatism, and, I could probably find just that “sweet” spot to put my projector and help out with the pincushion issue, however, I was really hoping that having a cylinder lens would be more forgiving than the Prisms? Perhaps not.
Something like the XEIT or ISCO would yes. But these are much more complicated lenses, the ISCO is (IIRC) for elements and the XEIT 5 elements, and both have mechanisms designed in for focus/astigmatism correction. I'm not sure if the threads got purged or if I just can't find them, but the XEIT Crystalmorphic lens is (it could be argued) a DIY lens. AussieBob designed and had that lens manufactured himself (going by my memory), but the result is not what I would call a "DIY" lens, he ended up with a commercial lens, and probably had to do that if only to get the order quantity high enough to make it even remotely affordable.
My main goal is to strive to get a better picture with less aberrations. I really do not want to perform the “zoom” mode and lose all those pixels. I really like the philosophy of anamorphic lens, and wish there were more options.
Unfortunately precision optics/mechanics are expensive. The best option I'm aware of, on the "inexpensive" front for cylindrical is Prismasonic's cylindrical offering.