I'm blushing with embarrassment. All this talk about a few words I wrote years ago AND I MISSED IT!!!
I'm an optometrist so I can easily get high grade glass cylinder lenses, with anti-reflection, for very little cost.
Anti reflection coatings are about 10% of the problem. Eyeglass lens blanks are not color corrected. Hence, if you build an anamorphic couplet using CR39, be prepared for all the colors of the rainbow from about halfway out to the edge of the screen.
Eyeglass lenses are meniscus lenses. Not suitable for anamorphic couplets. You will observe, not only color aberration, but also blurring anywhere but near the center of the image, getting worse out towards the edge of the screen.
No one on here will give you any info on how to build one, or more importantly, the optical settings due to the fact that they spent a bunch of time figuring it out and are now selling the products and don't want to lose out to DIY folk making their own. I personally think the cylinder lenses are marked up A LOT, but then again that's the market price until someone comes out with a cheaper version. But i could be wrong.
You turned out to be wrong about that. I gave out the information because there's a lot more to building an anamorphic lens than just the ratios of the focal lengths.
If building your own lens was this costly ("$$$$")and difficult to build your own cylinder lens then they would easily give that info out because they know you would fail and/or give up due to start up costs. So I'm thinking its not as bad as it sounds.
It's much, MUCH worse than it sounds. And incredibly expensive to prototype large chunks of anamorphic glass.
1/100ths of a degree would only be a measurement important to NASA definitely not to the system.
Wrong. 1/100th of a degree is a minimum for 1080p, and not good enough for 4K. Tiny miscalibrations can be fixed by counter-rotating the other lenses in the set in the opposite direction. But when it boils down to it the accuracy still has to be 1/100th of a degree, even if it's a kluge to fix something out of alignment. When you counter-rotate lenses to fix a problem you also skew the image. It's no longer rectangular, but rhomboid.
Nobody can correct it that close, in fact that amount of detail is insignificant for a optical lens for a HT.
I do, routinely. In fact our correction is better than 1/150th of a degree. It's easy (in a relative sense) when you invest in calibration equipment.
IF that were true then the guy that had the -6.00 amount of astigmatism in his glasses would not be able to see anything with glasses as all glasses are corrected on intervals of 5 degrees, no where near 1/100th of a degree.
You can't really measure whether something appears to be "level" to a subjective human perception, certainly not down to 1/100th of a degree. You CAN measure - very accurately - whether an anamorphically expanded image is level. The human eye, and its perception, are a completely different ball game to measurable, verifiable standards applied to scientific instruments.
If you make a system corrected to that detail and that is important to you then you need to get your eye prescription updated, for changes, every month!
Fatuous comment. The human eye is much more forgiving than a laser-calibrated microscope used for precise collimation.
It generally takes 4 cylinder lenses (cylinder lenses are the type used to correct peoples vision when they have astigmatism: ie eye shaped like an american football) The more lenses used, the more optical clarity that can be corrected for. But I haven't actually worked it out yet but the materials aren't that expensive nor do you need to work for NASA.
Eyeglass lenses are plastic, made to dramatically lower standards than very expensive cylinder lenses. The human eye can adapt focus and to some extent anastigmatic error. Projectors and projection lenses cannot. If they're wrong, they're wrong.
I now have hundreds of lens customers, optical freaks, who do "hi-fi fanatic" in their spare time. These people are unforgiving of the slightest flaw in their precious picture. they have invested thousands, tens of thousands and sometime hundreds of thousands of dollars in their theaters and production studios NOT to have it degraded by a dud lens (which is, after all, the final optical summation of their entire investment, as it is the last thing the image passes through before it hits the screen). There are no shortcuts to excellence. They need the best contrast, the best sharpness, the lowest distortion and the brightest images, virtually indistinguishable from the original, as possible. Some are private customers, some are in government, some in defence and film production. But they all share a common trait: they don't invest in garbage, and they don't like bulls*it.
Someone above wrote that I say a lot. Not so much lately, but if I do say anything it is this: there is no shortcut in optics. There is no dirty little secret that optical engineers keep to themselves, to chuckle about when they're having a beer with the other optical engineers in on the scam. There is only hard work, spiced with a lot of luck and many hundreds of hours of toil. You can't use eyeglass blanks, you can't bend a plastic mirror (another favourite) and you can't buy cheap trophy prisms to achieve the near-to-perfect results that customers demand. You have to work at it, keeping your environment scrupulously clean, ordered and as pristine as the day you first put it together. If you don't believe me, try the cheap approach. It won't work, but you MAY learn (the hard way) why it doesn't.