Making Lenses- VERY accurately. Pics.

[ImanCarrot]

I have a Diamond Turning Lathe and make lenses on it- I thought I'd post some piccies of my latest project- the lenses are hybrid aspheres.

For thosee who don't know what I'm on about, you can see what Single Point Diamond Turning is on Wikik here:

http://en.wikipedia.org/wiki/Diamond_turning

Anyway, I started by setting the tools up in Height and X- important otherwise the tool wears and you get a bad finish and form.

Next, I machining the vacuum sub- chuck edge- this has to be done so that the air bearing spindle is balanced. Similarly the front has to be faced. The finish was unimportant so I used a scrap diamond tool.

Next, I cut a diameter step in the sub chuck with a sharp carbide tool to push fit the diameter of the acrylic blanks, stuck the blank in and turned the vacuum on.

After programming the aspheric co- efficients in I then machined the blank using a new diamond tool.

And that's the finish I get... straight off the machine

Checking the form gives the Peak To valley error (or departure from true profile)- you can see this in blue in one of the photos. This means that across the whole 36mm diameter the deviation from true profile is 0.491 microns or for those who work in inches... 0.00002" (rounded up). Hehe good machine, good *pats machine on head*.

Will post more when I get the second face done.

[ImanCarrot]

More pics:

[MIKE JEFFERS]

lets see a pic of the whole machine

[ImanCarrot]

Hmm, don't have any pics of the actual machine- just took some, but it will be Monday before I can post them since I need to get them onto my home PC, but I can give you the manufacturer's link (needless to say I have no interests in this company other than I use their machine).

http://www.sterlingint.com/optoform50des.php

As a summary, the machine has an air bearing spindle, the slides are supported on air, the whole lot is supported on a crushed granite/ epoxy mix and this lot is supported on air cushion pads. The spindle is temperature controlled to about 1 deg C and when it behaves itself it a rather nice machine

[samco]

could this process be used to make primary mirrors for telescopes? How smooth is the finish? could it go right to coating?

(like 8 or more inches in diameter)

Very neat!

sam

edit - oops , just noticed you where doing plastic - not glass.

[RICHARD ZASTROW]

Iman, Iminpressed.

[ImanCarrot]

Thanks Richard

Hehe, and yep, I've made optical mirrors (some of them are up in satelites, others in all sorts of equipment)- primaries, secondaries... anything but in aluminium... I cant Diamond Turn glass, although some people say they can, but I don't beleive them cos glass is a supercooled liquid- I've tried it (but I'm not bigheaded enough to thing it can't be done). I also do Germanium optics for infrared scopes and stuff.

Here's some if the IR goggles my optics go into.

http://www.sts-eo.com/v2/index.html

(not connected with the company except to supply the lenses)

On glass I use traditional polishing techniques and can get down a twentieth of wavelength of light accuracy on form at 633nm over 12" dia, any further than this the optic is diffraction limited and you can't measure it (light starts diffracting).

Oh, obviously with aluminium you don't need to coat it, unless you want to go IR with gold or a protective TiO (silver raises the reflectivity of course though), the finish is military standard optical

[ajmoir]

Hi,
I have some optics questions, feel free to ignore but any help would be appreciated.

I'm in the process of building a laser distance measure, similar to the stanley max and leica models.

I have the basic idea worked out and also the electronics worked out using a micro processor, simple linear optical sensor and cheap laser.

The area I fall down on is optics i.e. can I get away with a pin hole or do I need a lens etc etc, real basic stuff.

Where do you suggest someone such as myself begins. I think what I need is the basic formulas needed for focusing e.g. how far from the sensor to place the lens of x strength to focus 3'-12'. But like I say I'm a real novice here. Is there an optical equivalent of CNCzone?

[Geof]

Originally Posted by ImanCarrot ... I cant Diamond Turn glass, although some people say they can, but I don't beleive them cos glass is a supercooled liquid- I've tried it (but I'm not bigheaded enough to thing it can't be done)...

I think the mirrors for the Keck telescope on Mauna Loa were turned.

[ImanCarrot]

Ajmoir,

It all depends on what level of accuracy you need, if you're looking for sub micron accuracy then you will probably have to use an interferometer (a phase shifting one will get great accuracy), there's a couple of sites I use which may help:

http://spie.org/
http://www.groupsrv.com/science/forum-22.html


Geof,

That surprises me! the 16 hexagon mirrors that make up each of the two Kecks are 2 metres in diameter (giving a 10 metre total dia for each telescope). To be able to diamond turn something as big as 2m is very impressive! The biggest I've done is off- axis parabolas about 1m dia.

Unless it's just some of the other optics that are turned.. I shall look into it.

Incidentaly, for those who don't know, the Keck telescopes are the largest in the world and will operate together (like a pair of binoculars) to get even more resolution and see things really far away.

[ImanCarrot]

Found it Geof,

Apparently the individual hexagon mirrors are traditionaly ground and polished, but they use an ion polishing process to do the final figuring- I've heard of this ion- polishing technique years ago, but didn't know it was in production.

The material it's made of is Zerodur which is a glass ceramic with virtualy zero co-efficient of expansion- I've worked this material ages ago using traditional hand grinding and polishing techniques- it's a lovely material to work- very very stable and you don't need to let it cool down after polishing, only trouble is it's a kind of amber/ yellow color and so no good for transmission optics, but it is perfect for mirrors after being coated (which I do as well

You cannot Diamond Turn zerodur and get an optical finish... beleive me, I've tried lol. Would be nice if I could... I'd make a fortune hehe, but if I remember correctly ion polishing involved removing material at the atomic level by bombarding the surface with Argon(?) so in a sense the mirrors were machined we engineers are good!

Here's a short extract and the link:

"Each of the 36 mirror segments (plus spares) was cast in a relatively easy process, ground to its proper shape in a special process under tension, and then finished using an ion-polishing process."

http://scikits.com/KFacts.html

[ajmoir]

Originally Posted by ImanCarrot Ajmoir, It all depends on what level of accuracy you need, if you're looking for sub micron accuracy then you will probably have to use an interferometer (a phase shifting one will get great accuracy), there's a couple of sites I use which may help: http://spie.org/ http://www.groupsrv.com/science/forum-22.html

The second link is very helpful, the problem is I don't even know what level of accuracy I need

The sensor I have has 5,000 cells in 35mm, 7microns wide, I've already hooked it up to processor and read it's contents, using a mask over roughly half the cells. Seems to work.

Ideally, I'd like to measure in a range of scales e.g. 0-3ft, 3ft-12ft, 12ft-36ft.

I'll pick up a few of the basic books listed in the forum and go from there. I'm pretty sure to get to started with I don't need anything to fancy, but if I want the full accuracy of the sensor at 40ft then I'll need to become more serious.

If nothing else my hobbies seem to improve the quality of the books in my bookcases