HIGH END DIY triplet projection lens

[ace3000_1]

In years past it took engineers months doing hundreds of calculations

Hehehehe try years bud but yeah i know what u mean, the age of computers my son has made life a whole lot easier and faster.

Trev

[ace3000_1]

One is to take the plans to an optical design firm and have them custom grind the lenses for you.

Ive looked into it hezz, $2k for the tooling on each lens for custom lenses, that price quote was from edmunds, and i dont see it much cheaper then that anywhere else.

Trev

[Hezz]

Trev,

That price quote doesn't surprise me. I know there are other companies who would do it for less but it still would not be cheap. I think my eventual design goal will be to make this lens into a tessar with some plastic lenses and then make the lenses by hand. The highest precision lenses have historically been made by hand until just in the last five years where advance CNC machines have taken over a lot of the production. However, most of the machines are designed to do smaller lenses of say less than 100 mm.

I will have to study some more on hand griding methods for lenses. Plus I will have to get a few more measuring devices and possibly a small surface plate. I already know how I can make the lenses relatively cheap from acrylic plate but I would need access to a CNC lathe and even though I have the CNC programming knowledge and access to the necessary software the cost of machine time is high.



Hezz

[Hezz]

Guys,

for those who are interested I think I have come up with a way to make this lens DIY style for a more reasonable price. It will still not be really cheap but maybe 200 - 300 dollars.

First lets talk about the lens and it's resolution. The way I figure it the average dot size for a high resolution CRT monitor is around .24 mm. This dot consists of three color pixels so lets say that for a lens system to accurately focus on these small objects it must be able to focus each subpixel. So we need a lens that can focus a spot size of .08 mm to be able to accurately focus the image.

Now I don't know exactly how the pixel size arrangement in an LCD corresponds to that of a CRT monitor but since most CRT's are somewhat higher resolution than a LCD I am going to assume that the LCD pixels are just slightly larger. So what this comes down to is that we need a lens system that can accurately focus an image as small as .08 mm or 80 microns.

AS can be seen in this spot diagram for the glass 40 degree triplet it can focus down to about 44 microns of spot size on the paraxial axis. I have compared it to a four element optimized glass tessar lens and the tessar is slightly better giving a 32 micron spot for the paraxial axis. For most application the slight improvement of the tessar over the cooke triplet does not justify the cost and added complexity. For us it shouldn't matter too much as the cooke has twice the on-axis resolution that we need.

Hezz

[Hezz]

OK,

now here is the procedure for the home manufacturing of this lens.

First the lenses will be compression molded in a small metal press with machined inserts.

A small home made kiln will be made that can heat small glass blanks up to a moldable temperature. This can be made realatively cheaply.

The exact lens volume will be calculated and core cut blanks of the proper glass type will be ordered. As far as I can tell these are relatively cheap. Maybe 20 - 30 dollars for each lens material.

The metal press will have stainless steel pucks that are interchangable that have the lens curves machined into them. This will be best done by CNC but can be done with a manual lathe by making some kind of curve jig.

The mold pucks will then be hand ground using conventional hand lens grinding techniques to get the mold cavities to a high standard.

Then we put the proper metal pucks into the press and we put the metal press on a small portable hot plate to keep the mold hot and put the precisely sized lens blanks into the little kiln until they are soft enough to mold. Then we put the softened glass blank into the press and compress the mold and wait for it to cool.

When it comes out it should be of very high quality and we finish the process by hand polishing each lens with a pitch lap.

Then we have the lenses coated with AR coating.

There is also the possibility of having the lenses mounted in a water tight lens housing and using index matching liquids between the lenses. Done properly this can work as good or better than AR coatings on the lens.

Hezz

[Hezz]

In regards to making a zoom lens design. I am of the opinion that it would be better to have a simple objective of the approximately correct focal length and then build a variable anamorphic lens system which can be easily removed from the projector. Please look at the anamorphic thread to see how some of those lenses were actually made in the past.

It is far easier for most to move the projector a little to get the correct picture size than to make a zoom lens.

Hezz

[z2895]

I don't know much about lens design or requirements, but when reading this thread one source came to mind for making custom lenses of various strengths cheaply, eyeglasses.

Is it possible to make a design which would use the size and strength of lenses producable by optomatrists? Perhaps the lenses would be too small, have too small a range of focal length, or not be precise enough, but I thought it might be a good idea.

Rather than having custom lenses made you could even use piece together a lens system with used eyeglasses for nothing.

[Hezz]

z2895,

The size and focal lengths that we are dealing with with this lens takes it outside of making it with common things like eyeglass blanks or even off the shelf lenses.

Typically off the shelf lenes are only available in sizes up to 80 mm in diameter and that is smaller than the smallest lens in this system. Also, getting the exact prescriptions would not likely be possible with off the shelf lenses.

Also this lens requires certain glass types to work properly and they would not be available in eyeglass lens blanks.

Hezz

[Hezz]

Posting something on this thread to get it out of the arcives for a time as someone has found possible builder of the lens.

Hezz

[Dantx101]

Greetings all.

First off, I am in the process of making my own projector and trying to figure out what projection lens to use has brought me to this thread.
I happen to operate the CNC lathe our company uses and am very interested in the possibility of manufacturing my own lenses. Metals are what we mostly deal in with stainless steel as the most common , although I have done some telfon machining.
I am not an experienced machinist by any means, I just happen to have enough knowledge to allow the company to justified the expense to support our valves and customers. If I try and am successful I would like to send a set to someone experienced here to examine and test them.
Luckily, I am the only one who knows how to operate the lathe and it can go for days without being used. If I dont have the tooling to do this then it wont happen due to the expense.

Let me know what you guys think