[twocik]

I'm looking for an optics guy to discuss a few things I need to have made.

- Focusing Screens (silent plain matte)
- Achromats lenses (72mm & 82mm)
- Prism


Chris

[twocik]

Anyone ??

[martinw]

I'm looking for an optics guy to discuss a few things I need to have made.

- Focusing Screens (silent plain matte)
- Achromats lenses (72mm & 82mm)
- Prism


Chris

Dear Chris,

There is someone called ImanCarrot on the Zone. I suspect he is quite good at what he does Try and send him a PM.

Just a thought,

Best wishes,

Martin

[twocik]

Thank you, PM sent.


Or if anyone here knows of another, please feel free...

[ImanCarrot]

*peeks around* Optics? optics? no-one knows about optics lol, even Newton had trouble with them! Michelangelo and the Medici Princes had trouble with them! Aristotle wrote a comedy about them! perhaps they were short sighted Gallileo said, hehe.


Well, in actual fact, I know a little bit I have been making lenses and prisms for more than 25 years, you would get less for murder lol.


I need to know your specific question. You mention achromats, which is basicaly an achromatic doublet- it corrects for chromatic abberation (like when you look through a kids pair of binnoculars and see colour at the edges- that's chromatic abberation).

Aspheric lenses are better than achromats at correcting chromatic and spherical abberations. I could write a book about this... so must be brief.

Optics in any project, whether it's a heat seaking missile, satellite, submarine pericospe or whatever, are always the main bottleneck, making them correctly is an incredibly skillful and labour intensive process (read as expensive)

Always make sure your design is perfect before saying "make this" to the engineer. The chap who made the Hubble Telescope primary made it perfect... perfectly wrong: cos they gave him the wrong design. Space folk had to go up and do a repair (like giving it a pair of specs). Make sure your design is RIGHT. Us chaps, who make the things, take a great deal of pride in perfection, especialy when it's in the palm of your hand and you think... "not a lot of folk could have made that" To hear "Oh, can we change the base radius of curvature" will not elicit a very happy response.

Don't forget coatings- they always improve the system quality.

[Edit]Buying off the shelf stuff will keep the system costs down- try www.edmundoptics.co.uk (I have no connection with this company, apart from being a satisfied customer)[/edit]

Ask away and I'll do me best to help, but it is Friday Bank Holiday here in the UK and I'm just back from the pub, so I may not get back to you for a few days if that's ok. Have a good weekend!

ps: Specifically what wavelength are you working at? 633nm, 544nm, 10.6um or something else.. just asking cos some high index polymers are extremely good at visible/ IR wavelengths and allow radical aspheric machining whereas glass can't really be maniupulated that way.

Dang! I feel like I've written the bible lol, ask away, I'll help.

Iain.

[rapidtraverse]

Righteous Dude!

You are a credit to Optics, this web sight, and yourself.

It's good to be able to access such knowledge.

Respect

[ImanCarrot]

Many thanks! nice to get +ve feedback.

Incidentally, theres a couple of Optics sites that I'm a member of, if anyone's got optics queries these guys rock:

www.photonics.com
www.optics.org
www.spie.org

They're all pretty heavy onthe physics and maths, but that's optics for you, you're manipulating light

Oh,
OSA (Optical Society of America) and
Imperial College, London are good too, but pro'lly a bit heavy for general enquiries.

Iain.

[ImanCarrot]

Update.. been PM'ing twocik on this for a while and here's where it's got in case anyone else searches the net and (obviously) can't see my private messages:

I think you're after something like this:

http://www.ephotozineshop.com/produc...1021798#images

To increase the light input on the front of the face I'd anti-reflection coat it- simple for me to do, but anything is if you've being doin' it for more than half your life hehe.

Obviously, the "grain" on the back surface should be less than the pixel size on your detector/ camera so you get a precise focused image.

Oh well! back to making lenses

PS, Seriously consider aspheric lenses, they are much, much better than spherical lenses.

[twocik]

Yes this is the screen (Canon Ee-a & Ee-s) I've been using. The screens are good, but produces crap bokeh and a little vignetting. I need a screen professionally made, but seems that not one company in the whole world makes them, besides canon ........






"To increase the light input on the front of the face I'd anti-reflection coat it- simple for me to do, but anything is if you've being doin' it for more than half your life hehe."


How does this work ? Can you explain or maybe even show a video of what you do ? :")








"Seriously consider aspheric lenses, they are much, much better than spherical lenses."


I took a look in my old optics box and found a aspheric lens that I order a long time ago. I'm going to make a case for it and see where I'm at. Not sure what lens the spherical is, but I was originally talking about the achromat. Not sure if you got those confused....

[ImanCarrot]

Antireflection coatings stop light from bouncing off the surface by destructive interference. This light can be reflected off other optical surfaces causing image distortion. Any good optical system will always have coatings, it lets more light into the system by constructive interference too.

Wiki do a nice explanation of the principle, it's a bit simplified and aimed mostly at spectacle lenses which are no where near the accuracy required for serious optical systems, but gives you the principle. Google "Antireflection Wiki".

In real life, we do multilayer broadband coatings for the visible, deposited under high vacuum using a plasma assisted system.

Achromatic lenses (achromats) are used to correct for spherical and chromatic abberations- light is composed of different wavelengths (like a rainbow), these are the only colours a human eye can see. Unfortunately, these focus at different points (simply put). Aspheric lenses correct for spherical and chromatic abberations much better 'cos you have less optical surfaces whith which to distort, absorb, reflect and refract the incomming light.

You'd need to speak to an optical designer to get the aspheric equation right though. They'd probably use Zemax software to do this and charge the earth lol.

I'd be very surprised if your achromatic lenses were not already coated, but the non- ground surface of your screen may not be- worth checking as interference between this 'face and your image plane might be causing the vignetting. If this is the case, then you definately need it AR coated or you could also have the screen made wedged- one degree of arc (TIR) usualy works in most systems. Don't wedge anything that's transmitting a divering or converging beam though- it introduces spherical unless you know which way to put the thick and thin side of the wedge in the system.

Do you know the grain size of your diffractive screen? how does this compare to your detector pixel size? (it should be less).

Again, an optical designer would help, I just make the stuff

I've PM'd you our web site which explains Optical Coatings properly.

Sorry for being so verbose, I have tried to be concise, but it's a bit of a black art is optics!

Hope this helps!

Iain.

ps- here's a simple illustration of the principle, but ours is better- the beam can hit the inside of the coating going through a phase change and thus add to the transmitted beam. If you know how to make that coating (we do).