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post #31 of 44 Old 02-27-2012, 10:10 AM
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For more info about playing around with eyeglass lenses, check out the what Aussie Bob says in this post:

http://www.avsforum.com/avs-vb/showt...9#post16518239

He talks elsewhere about experimenting with these lenses, too, and he's a wealth of knowledge and information.
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post #32 of 44 Old 02-27-2012, 12:01 PM
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Aussie Bob is my new hero. Thank you for pointing this out. I've been searching for exactly this information for a long time.

It would seem (and I believe his description) that eyeglass lenses are never going to be the next Isco, but my next question is could they be better than a set of prisms. The need for an 83mm air gap might also pose problems with the size of these lenses and the throw ratios of typical projectors.
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post #33 of 44 Old 02-27-2012, 12:19 PM
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He hasn't participated here in a while but you can contact him via www.xeitoptics.com if you want to chat about the technical details on lens design.


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post #34 of 44 Old 02-27-2012, 12:43 PM
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Quote:
Originally Posted by riskpeep View Post

Aussie Bob is my new hero. Thank you for pointing this out. I've been searching for exactly this information for a long time.

It would seem (and I believe his description) that eyeglass lenses are never going to be the next Isco, but my next question is could they be better than a set of prisms. The need for an 83mm air gap might also pose problems with the size of these lenses and the throw ratios of typical projectors.

I believe he said that you can't just order the correct size needed out of a catalog but it would have to be a custom cut piece which will add greatly to the price, at least when he made the post (09).

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post #35 of 44 Old 02-27-2012, 01:27 PM
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Yeah, I've noticed that about the largest lens blanks you can find are in the 100mm range, most are 70-80mm range.

One of the reasons I started looking at eyeglass lenses, is that outside of those, for high quality optics, most parts are in the 25mm or smaller sizes. The prices get ridiculous if you get up much past that.

I still haven't given up on the idea of using lens blanks, but reading aussie bob's posts have given me pause. I had heard that lens blanks aren't ground to the same precision as your average camera or projector lens, but to have it confirmed pushes me back a step.

My current like of research (if you can call google searching research) is to see if I can quantify the parameter we care about (surface quality?, surface deviation?), and then compare various kinds of lens materials to that to see how close I can find. Many firms now tout 'High-Definition' lenses that I think might be market speak for better surface quality or lower surface deviation. I'm still trying to figure out the market speak from the engineer speak (which is what I want).

I have no allusions that I'm going to create a $50 ISCO lens. But I'd like to think that we should be able to outdo your typical prism lens.
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post #36 of 44 Old 02-27-2012, 04:04 PM
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Quote:
Originally Posted by riskpeep View Post

Mark,

Thank you for your reply, this is helpful. Is the distance between the lenses particularly relevant, or just the alignment between them?

Spacing is absolutely critical and why I now have a massive threaded focus ring on the MK5.



Lets see if this gets me another suspension . At the distance it is set in this photo (recessed), the image is not in focus at my TR and projection distance. To be in focus, the threaded centre needs to protrude about 12mm extending the depth of the lens to about 140mm.

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I've been doing some additional research on this and what I know so far is that eyeglass blanks are measured in diopters. At the risk of being pedantic, a diopter (http://en.wikipedia.org/wiki/Dioptre) is a measure of the optical power of a lens and is the reciprocal of the focal length, so a 3 diopter lens would have a focal length of 1/3 of a meter. Lenses can be found in 0.25 increments of diopters.

Eye glass blanks are typically CR39 plastic these days and you should be able to specify a cylindrical cut at a specific diopter. As you see from the first image I attached, you need both a concave and convex lens pair. They can be "round" or "square". I've drawn then "square" because I could not get Sketch Up to allow me to cut the profile round after cutting the basic shape. Something about not being able to shift curved surfaces?

Quote:
The interesting bit is that for an eyeglass prescription (and thus for readily available lenses), you have a spherical measure (which is a general magnification), and a cylindrical measure. We only care about cylindrical power, so the appropriate lenses with the correct cylinder rating is what we'd need.

A blank should be a small cylinder - R=40mm H=10~15mm. They cut them to be spherical (both x and y axis) where a cylindrical lens is just one axis.

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My understanding is that for an Anamorphic lens, we want a 1.33x expansion lens which should be achievable with two lenses having the right ratio between their Diopter ratings. I found one person on the web who'd had success with experimenting at an anamorphic stretch using a -6 cylinder lens paired with a +4.5 cylinder lens, but he was using opthalmic test lenses with a diameter of ~1" and thus couldn't pass the whole beam of his projector.

I read that too and where 6/4.5=1.33. There are many other combinations that can give 1.33x

You should be able to use any two lenses with the correct ratio between them, so if I have this right, you could use a -6 & a +4.5 cylinder lens, or a -3 and a +2.25 lens.

Quote:
If we can find someone with access to eyeglass lens blanks and a projector, it would seem a simple test to put two lenses in front of a projector to see if we're approaching this problem right. Obviously you'd need to get the orientation right (being cylindrical lenses, they do have a directionality, and between the two lenses the directionality would need to be exactly lined up.

You might have to go to an optometrist and place an order for these lenses. If they can cut the precise multi-aspheric curves of corrective eye wear, I am sure that they can cut the simple single radii you need - especially because it is in just one direction.

Quote:
Yeah, I've noticed that about the largest lens blanks you can find are in the 100mm range, most are 70-80mm range.

One of the reasons I started looking at eyeglass lenses, is that outside of those, for high quality optics, most parts are in the 25mm or smaller sizes. The prices get ridiculous if you get up much past that.

Welcome to my world. I still have the very first plano convex lens I bought back in 2006. 25mm, BK7 singlet and cost me just $15USD. I do believe it is the 6D as described in that thread at DIY Audio, but I could not find a 4.5D concave to match for an anamorphic pair.

Quote:
I still haven't given up on the idea of using lens blanks, but reading aussie bob's posts have given me pause. I had heard that lens blanks aren't ground to the same precision as your average camera or projector lens, but to have it confirmed pushes me back a step.

Whist his posts are very informative, he tends to do that. I wonder how different thing would have turned out if I actually took his "don't bother" advise back in 2005?

Quote:
My current like of research (if you can call google searching research) is to see if I can quantify the parameter we care about (surface quality?, surface deviation?), and then compare various kinds of lens materials to that to see how close I can find. Many firms now tout 'High-Definition' lenses that I think might be market speak for better surface quality or lower surface deviation. I'm still trying to figure out the market speak from the engineer speak (which is what I want).

I have no allusions that I'm going to create a $50 ISCO lens. But I'd like to think that we should be able to outdo your typical prism lens.

Commercial optical surface finish is scratch and dig 60/40. That means the largest scratch on the surface of the glass should be no greater than 60 x 40 microns. There is not even a published spec for those trophies. All I ever got from the manufacture was something about a 4 step polishing process.

There is nothing wrong with SD 60/40 and in fact it is the spec used by at least 2 anamorphic lenses available today. Sure you ask for a better surface finish, but your lens set just cost you triple.
LL

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post #37 of 44 Old 02-29-2012, 02:05 PM
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Eye glass blanks are typically CR39 plastic these days and you should be able to specify a cylindrical cut at a specific diopter. As you see from the first image I attached, you need both a concave and convex lens pair.

Yeah CR39 is very common. Here in the US, you can get also find glass as well as a number of high index plastics although these cost more and can be special order items. If we can work out the finish quality and light path issues, my thought would be to use different materials to see what we could do with correcting CA. (that is a problem for another day)

Back to the lens design. If I'm doing my math right, it looks like the following lens combinations would work. I stopped at -10 because most lens blanks aren't available past -10, and for most retailers anything beyond -3 is a special order item.

Lens 1 Lens 2 FL1(mm) FL2(mm) Distance(mm)
-1 0.75 -1000 1333.333333 333.3333333
-2 1.5 -500 666.6666667 166.6666667
-3 2.25 -333.3333333 444.4444444 111.1111111
-4 3 -250 333.3333333 83.33333333
-6 4.5 -166.6666667 222.2222222 55.55555556
-8 6 -125 166.6666667 41.66666667
-10 7.5 -100 133.3333333 33.33333333

From Aussie Bob's post, I know that we need to space the lenses based on their focal lengths (FL1 & FL2 in the table), with the distance being the Distance column.

Since we have such small lenses to work with, I think we'd want to minimize the required distance between them to make sure that the light stays within the usable area of the lenses. A longer lens is going to need bigger glass to capture the 'fast light' coming out of a projector.

TR will also come into play here. I think I've got some math ahead of me to figure out what the ratio of input aperture to exit apertures are indicated by various throw ratios. It is possible, perhaps even likely that even for a long TR, that 80mm on the exit aperture won't do it even for a very short lens.

I've been told that most blanks are 80mm, so I'm going to assume that in my entry/exit aperture analysis.

SOHCAHTOA here I come.

Quote:


Commercial optical surface finish is scratch and dig 60/40. That means the largest scratch on the surface of the glass should be no greater than 60 x 40 microns.

It sounds like this would be a surface quality measure. Is there a surface deviation metric as well that is typical? (i.e. a measure of how true the shape of the lens is)
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post #38 of 44 Old 02-29-2012, 03:25 PM
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Quote:
Originally Posted by riskpeep View Post

Yeah CR39 is very common. Here in the US, you can get also find glass as well as a number of high index plastics although these cost more and can be special order items. If we can work out the finish quality and light path issues, my thought would be to use different materials to see what we could do with correcting CA. (that is a problem for another day)

AFAIK, the only way to correct for CA is to use a achromatic doublet which is two lenses made of different glass types that are cemented together to form a single lens.

Quote:


Back to the lens design. If I'm doing my math right, it looks like the following lens combinations would work. I stopped at -10 because most lens blanks aren't available past -10, and for most retailers anything beyond -3 is a special order item.

Lens 1 Lens 2 FL1(mm) FL2(mm) Distance(mm)
-1 0.75 -1000 1333.333333 333.3333333
-2 1.5 -500 666.6666667 166.6666667
-3 2.25 -333.3333333 444.4444444 111.1111111
-4 3 -250 333.3333333 83.33333333
-6 4.5 -166.6666667 222.2222222 55.55555556
-8 6 -125 166.6666667 41.66666667
-10 7.5 -100 133.3333333 33.33333333
From Aussie Bob's post, I know that we need to space the lenses based on their focal lengths (FL1 & FL2 in the table), with the distance being the Distance column.

In theory, all of those should give you 1.33x or 0.75x expansion based on how the light enters/exits the A-Lens.

Quote:


Since we have such small lenses to work with, I think we'd want to minimize the required distance between them to make sure that the light stays within the usable area of the lenses. A longer lens is going to need bigger glass to capture the 'fast light' coming out of a projector.

Bear in mind, I have a working example of an anamorphic lens made from what I believe are these eye glass blanks. The front lens is just 80mm diameter. The rear is closer to 60mm. The lens works at longer throws like 2.1.

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post #39 of 44 Old 02-29-2012, 07:28 PM
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Bear in mind, I have a working example of an anamorphic lens made from what I believe are these eye glass blanks. The front lens is just 80mm diameter. The rear is closer to 60mm. The lens works at longer throws like 2.1.

ORLY! How well does it work? From Aussie Bob's comments I'd think not so well, but I'm thinking he might be a bit of a purist. I've no doubt that your custom lenses are better, but how about as compared to your typical prism lens?
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post #40 of 44 Old 02-29-2012, 08:34 PM
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Quote:
Originally Posted by riskpeep View Post

ORLY! How well does it work? From Aussie Bob's comments I'd think not so well, but I'm thinking he might be a bit of a purist. I've no doubt that your custom lenses are better, but how about as compared to your typical prism lens?

AB has said allot of things

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post #41 of 44 Old 03-25-2012, 08:51 AM
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Is there anything from an old CRT lense that could be used? They are certainly big enough and looking at a cross section of a NEC XG lens from a brochure for example, I see every kind of shape imaginable in one lens. Some might be plastic though, but wouldn,t know until inspection. I have a few different lens available from different CRT projectors available also. Certainly easy enough to take apart.

So What are the physical specs of the lens you have made?
This might be a moot point if I understand the real specs as being either a concave or convex in one axis only of each lens?
Maybe one of these crt lenses has what it takes or maybe a certain mix to get there?
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post #42 of 44 Old 03-25-2012, 02:44 PM
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Not really as the lenses in those will all be spherical and you need cylindrical for this.

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post #43 of 44 Old 10-14-2012, 06:47 AM
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I wonder how much those lens from ISCO costs directly from manufacturer.

I can get them directly in Germany, this is why.

[]s,
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post #44 of 44 Old 10-14-2012, 08:58 AM
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Originally Posted by Gradius2 View Post

I wonder how much those lens from ISCO costs directly from manufacturer.

I can get them directly in Germany, this is why.
Fernando: Isco brand is only sold to OEM customers, myself included. Schneider branded lenses are sold to the dealer channel. None are sold to end users directly. That said, if you Email me I can price the Isco for you. We arrange for shipping to or inside Germany (and worldwide) regularly. scott at techht dot com.


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