Researching home-made lenses

[epatsellis]

Murray,
shoot me your address again, I have a few "largish" DCX lenses lying about that should keep you pretty busy....


erie

 

[Murray@uptowngallery]

The headache with software is physically realizing an optimized design wit ha budgetary problem...

or, identifying the properties of economical surplus glass that solve the budget problem.

Throwing all caution to the wind and just experimenting is the biggest element of luck.

 

[AgX]

Murray,

I once tried to download that Linos software, I could not install it; from then on I did not bother with such software. Thus I don’t know their properties.
But besides letting them freely calculate and construct just on the basis of glass recipes, could you not let them work on a catalogue of those off the shelf lens elements (no unidentified surplus thus)?
What could be the outcome of this?

 

[Struan Gray]

Struan,
many thanks on commenting on these thoughts on home made lens element, especially on the bearing problem; I would like to reply on this with a pun, bit it only works in German: I thought, "daß verschleift sich schon"...

Ich glaube, daß ich seinen Witz verstehen habe. Meine Antwort ist ein "englisch" Klassiker: "Illegitimi non carborundum".

And on software: such a software is to be downloaded for free from Linos (and Edmund?), they even recommend it to their customers.

Oslo is the program most frequently recommended by my optics friends. The free version lets you do simple doublets and - I think - triplets, but not a Tessar. Otherwise, if you have access to an old fashioned library, the analytic optimisation of something like a Cooke triplet isn't too scary. In Germany, the bound volumes of standard university physics textbooks from the turn of the last century usually include an optics 'bund' with quite detailed ray-tracing analyses. They are often sold at pennies per yard in secondhand bookshops.

Last time I played with the idea of making a decent lens for myself, the problem was finding a good variety of flint elements available off the shelf. If you are going to try and acromatise your homemade lens it is probably best to fix the flint element(s) according to what is freely available and then look for the least bad crown glass complements. Or - simpler - grab some achromat doublets from surplus sources or old telescopes/binoculars and use them as your basic building blocks.

We've used some of the E.European custom optics houses (mostly ex-military specialist suppliers in Latvia and Lithuania). The good ones are very, very good, but they're no longer cheap. They also deliver what you ask for, which isn't necessarily what you want. Someone like Edmund Optics will hold your hand to a greater extent.

It bears repeating: lenses are currently very cheap compared to getting any optics or machining work done on a custom basis. I bought a 270 mm Apo-Gerogon for €20. Coated, sharp and it covers 8x10 well. I also bought 420 mm and 240 mm Apo-ronars for less than the going price of their shutters: the glass had negative value on the market. I love bokeh (see Dead Link Removed and Dead Link Removed) but for now at least I want things in focus at the edge of the frame, so the vignetted by fuzz look isn't for me.

The flip side of that is to note that a good source of surplus elements is cheap lenses. Plasmat single elements have double to triple the focal length of the combined lens. Tessar front elements (n.b. elements, not group) have about three times the focal length of the combined lens. Half a super-angulon gives a funky normal lens. You can have a lot of fun for little money.

 

[Murray@uptowngallery]

Outcome - I would learn something. I'm not sure whether it would be another detour.

The beauty of surplus items is that you know you can have them. I have not tried many of the online optical material places, but with some, the cost pushes you toward just buying a used lens. Also, the ones I visited only offered one type of glass as stock. All else was custom with minimum orders.

I believe the software packages will allow you to select from 'virtual' off-the-shelf items that are pre-characterized & ready to simulate/design with.

Certainly using the pre-loaded info is the place to start, because it confirms ones ability to move to the next step (if info for the surplus is ever attained). I think it is possible to get reasonable radii with a spherometer and measure index of refraction at a couple of hydrogen line wavelengths and calculate Abbe numbers from the latter. Now, can I get access to the equipment to do that & how much work is it? I don't know.

I'm going back to school (again) in the fall; maybe I can talk someone into letting me do some measurements. They've got to have some appreciation that I'd rather do that than the usual college student weekend behavior.

I'm making noise on this forum hoping to find someone who's been there, done that.

 

[Murray@uptowngallery]

I'm also gambling that coated surplus stuff in different shapes (DCX vs. PCV) were made for different applications and made it far enough in the mfg. process to be coated, then rejected (chips, digs etc in my received pieces...grrrr, but cheap, oh well).

Looking at lens recipes, I often see one type of glass used for positive and and another type for negative.

But Murray's Law tells me that I happened to choose surplus from a monochromatic design and the gamble above is moot.

As Struan said, it'll be fun, I'll learn something, and at least here there is a sympathetic group, as opposed to photo.nit, where any hint of DIY activity seems to give the big-$ people hemorhoids.

 

[Struan Gray]

Go for it. I think it was Ross (as in Xpres etc) who really did make his first lens from the bottom of a bottle.

I don't know if Mark Sawyer does the APUG thing, but he's posted some excellent expressive still lifes done with home-made lenses over at largeformatphotography.info (a search on 'carrot' finds him efficiently).

The standard optical glasses found built into the design programs are those that Schott or Hoya will sell you as bulk glass or lens blanks. Not cheap though, unless you're making a lot of lenses. Telescope makers are good at finding alternative sources for small orders, so google objective grinding to see how they do it.

I can't speak for all academics, but those I know (including myself) are usually thrilled to find a student who is interested in more than the bare minimum for a pass grade. US colleges can be a bit less flexible about who gets to use the machine shop or the optics lab after hours (they get sued too often, it's not their fault), but a winning smile and a dollop of enthusiasm goes a long way.

 

[Struan Gray]

PS: I just noticed that the current issue of American Scientist (n.b. not Scientific American) has a good article on the largest current rotating mercury primary mirror telescope:

http://www.americanscientist.org/template/AssetDetail/assetid/55126?fulltext=true

Problems include air currents disturbing the mercury surface, wobble of the air bearing, mercury safety for the observers, and a mouse that ran about on the rotating mirror, too frightened to jump off

Cheap at $1 million or so.

 

[Murray@uptowngallery]

I got some practical answers on sci.optics to help me ID my mystery glass. It'll be algebra practice if nothing else.

 

[Murray@uptowngallery]

There is apparently no practical way to measure index of refraction and dispersion once a flat glass sample has curvature. While flat or a prism, it would be some work, but doable...grrrrrr

I am now reduced (last idea) to weighing them (easy to get accurate data) and measuring water displacement to calculate volume then density. Glass density is spec'ed in optical glass catalogs.

Problem is the lenses are too big (4" diam) to fit into any graduated cylinder I've run into, and a beaker won't give accurate info. I'll have way too many digits with a lab scale for mass, and not enough digits for the volume measurement :O(

 

[AgX]

Combine the graduated cylinder and the beaker...

Make a mark on that beaker at the second stage. Take out that lens and fill up again from that cylinder. You could add wetting agent to increase accuracy by reducing `take over´ of fluid by the sample.

Or make two marks, empty and clean the beaker and fill up from the cylinder.

 

[Ole]

I am now reduced (last idea) to weighing them (easy to get accurate data) and measuring water displacement to calculate volume then density. Glass density is spec'ed in optical glass catalogs....(

Cant you measure it, and calculate the volume from that? I'm sure that would be more precise than a beaker...

 

[AgX]

Murray might have one if those aspheric elements...

 

[Dan Fromm]

Murray? An asphere? Not him, they're too expensive. But he does have an irregularly chipped lens.

 

[epatsellis]

He has a nice multi coated 5" diameter meniscus aspherical on it's way to him this week, in addition to a few other very large diameter optics in fact..

erie

 

[Mustafa Umut Sarac]

AgX , I researched about diamond turning of glass and i found many pages which tell about positive results.
For example , 1000 year old rock crystal aspherical viking visby lenses , rodenstock people examined these lenses and they found that they are perfect as 1950s aspheric lenses. If you look for it at google , you will impress with their design. Researchers say they are made with turning lathe.
If some folks did it 1000 year ago , you can do the same today. As I said vibration is major problem and lens production lathes use two spindles. First for the raw cut and second is the precision cut. Second one have hydrostatic bearing . Some say they use gem quality diamonds.
I have a idea about magnetorheological finishing. If you look rochester web site on mrf , you find there many explanations.
As everybody says , you have to have algorithms , knowledge about every detail and their effect on lens etc etc.
You will have to have a polisher after diamond lathing. I think someone can create a mrf machine from scientific papers without changing any variable or using any computer code.
A basic wet polishing machine which works with try and see method , experimental.
And there is new lens making methods , multilayer diffractive optics which developed by canon 10 years ago. These plastic films reduced the weight
1/3.
And there is even more camera making options. You can see micro sar at byu.edu , its synthetic aperture radar. In germany , there is thousands of ham operators who have knowledge about 3 ghz. I think it is the ultimate point at photography. If you dont want to be exposed by synthetic radiations , you can even use sar satellites as the transmitter and you are the receiver , this is passive radar and you can watch 45 minutes video on diy radar at google search.
Lensless photography , here is one , electronic.

Best ,

Mustafa Umut Sarac

 

[Mustafa Umut Sarac]

The down side of radar photography , you have to move as a receiver. But i dont know what have to do if transmitter moves.
At byu.edu , there is also car sar. it is used to record a mountain valley and it is inspiring. At google , you can find related pdf files , circuit diagrams , used parts etc. And you have to look at byu library also , there is good micro sar thesis papers hidden there also.
If you want to be even more smart , you can add a super conducting circuits also .Micro sar is the latest , lighest and cheapest one.
They are talking about 20000 dollars but i looked to prices of the parts and you can do it cheaper than linhof lens.
All you have to need a electronic engineer who has experience with diy ham radio. It is not easy at Istanbul - where visby lenses believed to manufactured - but you can do it there.

Best ,

Mustafa Umut Sarac

 

[Mustafa Umut Sarac]

AgX , if taking birds , butterflys , crying children , sunset , palm beach photographs do not satisfy you , and if they seems to you as not important subjects , you can mess with whole earth 3 d photography for to find mineral deposits or oil fields under germany
I will describe here , how you will set up for your bigger than planet , smaller than galaxy photographs.
As you know , i wrote about synthetic aperture radars which uses centimeter long waves. For to research 1000 square miles oil deposits under 4 kilometers earth crest , you need extremelly low frequency waves. These waves are hundreds of kilometers long waves. As you know from satellite sar photography , you need a transmitter , transmitter antenna and a receiver.
You can say I can do that , of course you can but read this first you need an antenna 150 kilometers long , thick and heavy and lots of electricty. Where can you find such a long cable ? What about train rails ? Of course you need a permit from schroder for to use his train rails , you need 200 ampers electricty and lots of people for to keep people off from the rails. Preferably , you have to buy phosphor color jackets and helmets and lab googles to these people , lots of money again. I watch discovery channel and saw that european researchers have a fashion and its good to work with hot fashion lab chicks.
and and you have a computer loaded with us government earth crest maps , 3 d radiation propagation simulation software. Some say a computer with 2 ghz ram can do this.
And you have to construct your squid magnetometer with superconducting wires and liquids.
If a single planet do not satisfy you and you want to learn the chemistry of distant planets , gas clouds , go to diy spectrometer , astrophotography.
If you want still bigger shots , you can go to radio astonomy and count the quasars.
Still diy camera subject focused to non traditional photography.
If you do the photography with your zenit but at distant stars , i advise you to look at beam me scotty stuff

Best ,

Mustafa Umut Sarac

 

[Mustafa Umut Sarac]

medical imaging can be good also , ultra wide band or terahertz imaging , diy tomography , phhwww....

 

[Murray@uptowngallery]

Looks like bouyancy/Principle of Archimedes dry weight and apparent weight in water with some trick of hanging the item being weighed so it is in a vessel of water but not touching the bottom can provide accurate density with minimal calculation.

 

[AgX]

Thought about old Archimedes and my lab lever scale too. But I was not sure about that holding devise. Most probably one has to do 4 measurements, two for that device and two for the device with the lens attached.

 

[Mustafa Umut Sarac]

I was thinking that I had been written everything cover colors of imaging technology. There are even more. Wet etching is the same class technology with magnetorheological finishing but it does not require to be electrical engineer for to design magnets and need of cleaning expensive magnetic liquids.
Hydrofluoric acid is the enemy of glass and it melts the glass. Same kind of chemicals and creating a wet point on the glass can make your lens.
Well , it is my part to put the news in front of you , your part is to realize it.

Best ,

Mustafa Umut Sarac

 

[freygr]

Hydrofluoric acid, that is very nasty stuff. I would not want that around my house. If you are not careful you could lose fingers, skin, and/or much more.

 

[Mustafa Umut Sarac]

Freygr , do you know more friendly chemical for to etch the glass ?

 

[Mustafa Umut Sarac]

Here is the list of patents about magnetorheological finishing.No 27 and 26 is so detailed and i beleive someone who has strong will - like me - can make a mrf machine. I think it is an russian invention and came to usa with cold war ways. If you search with numbers , here is the link.
Agx I think you interest with it , i m dreaming to carve a flat piece of glass ... phwww...
http://patft.uspto.gov/netahtml/PTO/srchnum.htm
1 7,224,469 Optical system alignment system and method with high accuracy and simple operation
2 7,162,302 Magnetically shielded assembly
3 7,156,724 Method and apparatus for forming a dynamic magnetic seal using magnetorheological fluid
4 7,127,294 Magnetically shielded assembly
5 7,091,412 Magnetically shielded assembly
6 6,971,391 Protective assembly
7 6,955,589 Delivery system for magnetorheological fluid
8 6,927,922 Imaging using a multifocal aspheric lens to obtain extended depth of field
9 6,925,840 Method of making a photonic crystal preform
10 6,920,765 Combined advanced finishing and UV laser conditioning process for producing damage resistant optics
11 6,893,322 Method and apparatus for measuring and controlling solids composition of a magnetorheological fluid
12 6,852,219 Fluid separation and delivery apparatus and method
13 6,819,438 Technique for fabricating high quality optical components
14 6,746,310 Uniform thin films produced by magnetorheological finishing
15 6,740,194 Apparatus for etching or depositing a desired profile onto a surface
16 6,719,611 Jet-induced finishing of a substrate surface
17 6,561,874 Apparatus and method for abrasive jet finishing of deeply concave surfaces using magnetorheological fluid
18 6,555,017 Surface contouring by controlled application of processing fluid using Marangoni effect
19 6,506,102 System for magnetorheological finishing of substrates
20 6,309,285 Magnetic wiper
21 6,267,651 Magnetic wiper
22 6,106,380 Deterministic magnetorheological finishing
23 5,951,369 System for magnetorheological finishing of substrates
24 5,839,944 Apparatus deterministic magnetorheological finishing of workpieces
25 5,804,095 Magnetorheological fluid composition
26 5,795,212 Deterministic magnetorheological finishing
ABOVE PATENT MUST BE A READ
27 5,616,066 Magnetorheological finishing of edges of optical elements