$2K+ a-lens worth it? - Page 5 - AVS Forum
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post #121 of 145 Old 07-27-2009, 01:09 PM
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Quote:
Originally Posted by Aussie Bob View Post

I was going to quote more but this will do. Just a few random thoughts...

The main advantages of cylinder lenses over prisms are their ability to continuously adjust astigmatism, their relative lightness and degrees of freedom in design, the latter of which allows at least partial correction of some of the defects that are part and parcel of prisms systems (corrected or uncorrected) like geometric distortion.

A thoughtful cylinder design will reduce geometric distortion which prisms can never do without complex extra elements (which will be cylindrical, which renders prisms pointless anyway).

Much of your tolerancing objections to cylinder systems apply equally to prisms, especially tilt and rotation (which is just Z-axis tilt I guess). So let's not get too excited about this.



Oh please... "diamond turning" is easy to say but very expensive, and once you add a curved surface to the prism you are introducing potential tilt tolerances as well as making the system cylindrical, or at least hybrid cylindrical. Why not just make the whole thing cylindrical and be done with it?

Don't want to get into an esoteric flame war type of thing here (7th order aberrations are definitely esoteric) but you're underrating the astigmatism performance (or rather, lack of performance) of pure prisms. It's very noticeable and quite annoying without correction (as my illustration above seeks to demonstrate). If the pixels in the illustration were twice the size (i.e. if the projector was 960x360) you could see those pixels relatively clearly, but at true high definition you can't with uncorrected prisms. The illustration is modelled (not a direct photograph), but my observations of an actual system that the model was based on (where the incident planes of each prism were perpendicular to the axis of the beam) confirm it. And this is from ten feet away, not three inches from the screen. Raw prism astigmatism stands out like dog cojones. Which brings me back to the continuous adjustment concept that really only cylindricals offer. With continuous adjustment you get the very best at any projection distance, not just at the sweet spot.

I agree that there are a lot of mugs out there who pay too much for only incremental performance improvement. I've read the +$20k threads too. By the same token, that doesn't mean everything that's expensive is automatically a rip-off (although I'm on record as saying I believe Iscos are too much for what they do).

I guess we could argue forever over this. I'm happy you're happy. Shall we leave it at that?

Re. Pincushion at the sides
Yes there is some, but it's way lower in proportion than 27/64ths of the pincushion at the top, actually about 1/4. This is because there's no optical power in the vertical direction. The pincushion down the sides is residual, and can be discounted as negligable (say less than 0.25% at a throw ratio of about 2.0).

We will agree to disagree with one final comment. I agree diamond turning is expensive having designed berylium aspheric mirrors for extremely expensive telescopes but that is exactly how Shawn at Panamoprh makes those prisms. Thanks to our bloated military budget he was able to get the equipment surplus for a song

There are more things in heaven and earth, Horatio,
Than are dreamt of in your philosophy.
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post #122 of 145 Old 07-27-2009, 01:09 PM
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Quote:
Originally Posted by Jason Turk View Post

I think you answered your own question...you said you were "still very happy". Why test fate (and your wallet)?

Yeah, your right. But how long will I be happy before I feel the need to upgrade?

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post #123 of 145 Old 07-27-2009, 01:14 PM
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Originally Posted by GoCaboNow View Post

Yeah, your right. But how long will I be happy before I feel the need to upgrade?

I used this in another AVSForum section:

Keep reading = Keep spending

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post #124 of 145 Old 07-27-2009, 01:21 PM
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Quote:
Originally Posted by Jason Turk View Post

I used this in another AVSForum section:

Keep reading = Keep spending


Crap, I am reading again...

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post #125 of 145 Old 07-27-2009, 01:22 PM
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Very true.

See what an anamorphoscopic lens can do, see movies the way they were meant to be seen
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post #126 of 145 Old 07-27-2009, 04:48 PM
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Cha-ching! I can hear the cash registers going...
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post #127 of 145 Old 07-28-2009, 03:48 AM
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This is an informative, educational and extremely interesting thread.

Quote:
Originally Posted by mlang46 View Post

Nice explanation but in the Panamorph 480, they have curved surfaces to correct the Astigmatism and I have seen no degradation of resolution at all in my system...

I can attest to the above statement. It is well and truly 100% correct. This is same as my experience with Panamorph UH480. It is unbelievably good. I cannot see any degradation to the pixel structure other than some softening towards the edge. That softening affect is still there (to a lesser extent) with vw60 primary lens. I think it is due to the difference in distance from the lens to the middle and the edge of the screen. Apart from that, it produces a crytal clear pixel structure and test pattern, No notable chromatic aberration - can see very small amount towards the edges when close to the screen. It has some geometric distortion and pincushion and I believe my low throw distance (about 1.8) must have contributed to that.

The major plus is the clarity and the brightness of the lens. I cannot imagine how this can be further improved. I haven't seen an ISCO or AVS1R/H5000R in action, so I cannot compare.
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post #128 of 145 Old 07-28-2009, 03:53 AM
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Quote:
Originally Posted by mlang46 View Post

I agree diamond turning is expensive having designed berylium aspheric mirrors for extremely expensive telescopes but that is exactly how Shawn at Panamoprh makes those prisms...

If you could please further explain how Panamorph lenses are different (if that is the case). Which surfaces are curved etc and how that contributes to the clarity. Thanks.
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post #129 of 145 Old 07-28-2009, 05:23 AM
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Quote:
Originally Posted by syncguy View Post

If you could please further explain how Panamorph lenses are different (if that is the case). Which surfaces are curved etc and how that contributes to the clarity. Thanks.

Just a guess: The prism faces would be flat and the curved surface(s) is on the corrective element (at the rear).

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post #130 of 145 Old 07-28-2009, 11:52 AM
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Quote:
Originally Posted by syncguy View Post

If you could please further explain how Panamorph lenses are different (if that is the case). Which surfaces are curved etc and how that contributes to the clarity. Thanks.

A prism is essentially a tilted plate as far as estimating how it distorts the beam or changes the resolution at the screen. Smith Modern Optical Engineering page 135

If the light coming out of the projector was parallel the prism system would introduce no aberrations Smith p134 but the light coming from the projector is slightly converging so aberrations are introduced in to the image. In the projector system in my house 14 ft from the screen the convergence has an angle of only .25 degrees almost parallel. The steeper the convergence angle the more aberrations you have and the more aberrations you have the more the image is degraded at the screen. In this case only a small amount of astigmatism is introduced by the anamorphic prism expander and it can be completely eliminated by either introducing a weak cylindrical surface or a tilted spherical surface which you can do by micro-machining that curvature on one of the prism faces with a diamond turning machine.
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post #131 of 145 Old 07-28-2009, 12:14 PM
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Quote:
Originally Posted by syncguy View Post

I cannot imagine how this can be further improved. I haven’t seen an ISCO

The art of prism lens has really matured. The correction that everyone is talking about is fixed with a Prism lens and if your throw happens to fall into that range you will suffer no added CA. The Isco and most cylinder lens have an adjustment for CA so they are a bit more flexible with placement but this additional flexibility comes at a cost.
Unless doing a direct side by side you will be quit pleased with today's Prism lens.
They do cost you little more "light and contrast" loss then a cylinder lens but it is negotiable. For the perfectionist placing the Isco in front of projector its almost as good as no additional glass being there.
I use both designs switching between the two depending on which projector I am using and its throw requirements. I am not loyal to ether camp but do prefer the use of a lens for cinema scope content.
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post #132 of 145 Old 07-28-2009, 12:17 PM
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Quote:
Originally Posted by Alan Gouger View Post

They do cost you little more "light and contrast" loss then a cylinder lens but it is negotiable.

So how do you convince it to lose less?

See what an anamorphoscopic lens can do, see movies the way they were meant to be seen
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post #133 of 145 Old 08-20-2009, 07:09 PM
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Perfectionist= An individual with too much money and too few hobbies.
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post #134 of 145 Old 08-20-2009, 07:23 PM
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Perfectionist= An individual with too much money and too few hobbies.

I'm more the frustrated individual with too little to afford what I want or to do it right! Additionally, way too many 'EXPENSIVE' hobby interests......

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post #135 of 145 Old 08-20-2009, 08:12 PM
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Originally Posted by GlenC View Post

I'm more the frustrated individual with too little to afford what I want or to do it right! Additionally, way too many 'EXPENSIVE' hobby interests......

Now that sounds familiar

See what an anamorphoscopic lens can do, see movies the way they were meant to be seen
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post #136 of 145 Old 08-21-2009, 05:53 AM
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Perfectionist= An individual with too much money and too few hobbies.

I wish.
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post #137 of 145 Old 08-21-2009, 07:14 AM
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Quote:
Originally Posted by mlang46 View Post

If the light coming out of the projector was parallel the prism system would introduce no aberrations Smith p134

That would be one hell of a large anamorphic lens in that case - 3/4 the width and full height of your 'scope screen!

Quote:
Originally Posted by mlang46 View Post

but the light coming from the projector is slightly converging

Do you mean converging or diverging?

There are 10 types of people: those who understand binary, and those who don't.

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post #138 of 145 Old 08-27-2009, 04:09 AM
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Originally Posted by HogPilot View Post

That would be one hell of a large anamorphic lens in that case - 3/4 the width and full height of your 'scope screen!

He is referring to a Pass through mode and even non CA corrected prisms do not show CA. There is just no optical (anamorphic) stretch either

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post #139 of 145 Old 08-27-2009, 04:25 PM
 
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He is referring to a Pass through mode and even non CA corrected prisms do not show CA.

No he's not actually. The ideal beam for any anamorphic system has parallel rays. Projection systems have, by their nature, converging rays, and hence are not ideal for anamorphic systems.

When you put two prisms in an anamorphic configuration they work best when the beam entering the system has rays which are parallel to the optical axis. For example, a diode laser system with inherently parallel rays, but which (due to the nature of laser diodes) natively produces an oval-shaped or elliptical spot, can be made to produce a circular spot with a set of anamorphic prisms used to widen the narrow waist of the spot. This is a common solution to oval-shaped laser beams.

However, when the rays are converging, that is coming from ray pencils of a definite diameter at the projector end of the beam to a theoretically single point on the screen, the theory of anamorphic prisms is tested, and begins to exhibit aberrations (particularly astigmatism and color aberration). Because the rays entering the anamorphic lens are not parallel, the exit angles are not quite maintained enough to ensure a perfect spot.

In the end this means the larger the throw ratio, the closer to parallel the projector beam rays are, the closer to ideal is the performance of the prism system. This is why prism projection systems worked so well in large cinemas, where the throw ratio would typically be greater than 3.5. In HT applications, with some trying to use TRs of as little as 1.5 and 1.6, prisms perform poorly, as this is a long way from their ideal working environment.

Incidentally, cylindrical lenses designed for theoretically parallel rays perform in a similar manner to prisms in the same parallel-ray environment. However, prisms are fixed in form: four plane surfaces (the angles may vary, but the topology of all prism systems is basically the same). Cylindricals, while they can and often are designed with a "parallel-ray" model, can also be specifically designed for a sharply converging rays typical of HT applications.

In short, cylindrical systems have a better chance of delivering better performance in HT applications than prism systems. The caveat is that this potential performance advantage is always dependent upon proper design. A poor design of any optical system will not take advantage of any inherent strengths that system may offer on the drawing board.
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post #140 of 145 Old 08-28-2009, 09:07 AM
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Quote:
Originally Posted by syncguy View Post

This is an informative, educational and extremely interesting thread.

+1!

It has helped me change my upgrade plans.

I started off with a Runco CL-700 projecting on a 16x9 screen. Then I got the scope bug (wish I had discovered this site earlier.) I got a deal on a Panamorph U85. It made my 720p projector look better on scope material. Of course, my image didn't get any bigger, because the U85 is a VC lens.

Next I found somebody who heard I wanted to upgrade and offered to buy my U85. I sold it, and with a little cash in hand (and a small budget) I purchased a HTB two-prism HE lens. I already knew the limitations of such a design, but my wife knew the limitations of the HT budget.

Anyway, the HTB worked fine, but showed the limitations of my Graychip 1 DLP, now that it was being projected on a larger screen (for scope movies, anyway, which is what I watch, mostly.)

Couldn't find a buyer for the Runco, but I found a deal on a used Sharp XV-Z20000 1080p DLP. Now I'm cooking with grease! (Nice PJ, BTW.)

Anyway, yes on test patterns I can see CA, but I don't notice it much when viewing content.



Anyway, I was always planning to save up for an ISCO III. I might just aim for a UH480 now. As to the OP, the Sharp originally retailed for $12K, and it has often been praised for its optics, so I figure spending big money for a lens for this PJ would be appropriate.

Lastly, I'm into photography a little as well, and I know that in optics you get what you pay for.
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post #141 of 145 Old 08-28-2009, 10:16 AM
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Yeah, the ISCO is surely a great lens, I'd love to have one. But there's no way I'd buy one, well not in my current situation (if I get a huge raise or something, I'm not going to rule anything out ).

This hobby is all about balance, there are huge price and performance ranges in every aspect of it, from screens, to lenses, projectors, video processors, audio, speakers, etc, etc.

For me, the ISCO comes down to... Which will give you the best, most satisfying result:
  • $7k lens + $2k projector
  • $2k lens + $7k projector
  • $2k lens + $5k projector + $2k in pocket for more fun stuff


See what an anamorphoscopic lens can do, see movies the way they were meant to be seen
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post #142 of 145 Old 08-28-2009, 10:22 AM - Thread Starter
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Quote:
Originally Posted by stanger89 View Post

Yeah, the ISCO is surely a great lens, I'd love to have one. But there's no way I'd buy one, well not in my current situation (if I get a huge raise or something, I'm not going to rule anything out ).

This hobby is all about balance, there are huge price and performance ranges in every aspect of it, from screens, to lenses, projectors, video processors, audio, speakers, etc, etc.

For me, the ISCO comes down to... Which will give you the best, most satisfying result:
  • $7k lens + $2k projector
  • $2k lens + $7k projector
  • $2k lens + $5k projector + $2k in pocket for more fun stuff


You and I are in the same shoe except even a huge raise I won't be able to do a $7K lens

Also, I won't get a $7K lens for a $2K PJ, Panny 3K I have today. At the minimum I want to get something like a JVC 750 level of PJ before I'll start to dream something like a ISCO too.
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post #143 of 145 Old 08-28-2009, 10:33 AM
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Yeah I snagged a Panamorph P752 from a forum member a few years back. I think either the AVS1 or the UH480 are next on my upgrade list. Looking down the road, I doubt I'll ever get an ISCO, I just don't think I'll be buying projectors that "deserve" that sort of investment.

But heck, if I win the lottery (would have to play it first ) and get a Lumis-class machine, then hey, all bets are off

See what an anamorphoscopic lens can do, see movies the way they were meant to be seen
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post #144 of 145 Old 08-28-2009, 12:54 PM
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No to get off topic, but none of us appear to be very helpful. Just noticed my "thanks" counter in the avtar box....
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post #145 of 145 Old 08-30-2009, 12:55 PM
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I noticed those thanks points too. But only for a day, now those are gone.

The other day, Alan Gouger's name was changed to Lancelot Link and now its back to original. I wonder what they are upto.

Manoj
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