Where can one find a Coddington-like lens?

[Donald Qualls]

A simple macro lens will let you fill the frame with a 35 mm slide. For "high density" optical storage like that, you're essentially reinventing microfiche, only with digital data. A macro lens combined with a film positioning frame would almost certainly work better than an all-glass solution. Be sure to include error correction methods...

 

[jsmoove]

Thanks, yeah I had already tried with a 10x loupe actually, and it resolves the film pretty fine....I'm definitely stubborn though, all-glass is what I'd like to experiment with
There must be some sort of lens out there that has equal focal length to thickness, im just not sure of the correct terminology to find one

 

[jsmoove]

Question...a double convex lens' focal length is measured from its center, is that right?
http://doriclenses.com/optical-components/img/cms/Double Convex Aspheric lens.jpg
So if I found a double convex, it would need a focal length half of its thickness then
To arrive at a working distance of zero
Do I have that correct?

 

[Donald Qualls]

I think it's very unlikely you'll find any lenses like that. A lens that focuses on its own surface is a very specialized item, and I doubt there have been any made since Stanhope viewers went out of fashion.

You might contact your local telescope making club; I'm pretty sure they'd be very happy to welcome another addict, er, amateur optician to their ranks. There's no question you can make a lens like what you want, and those guys will even be able to give you the formula you need to figure out exactly how much to thin it after you have the curve ground and polished -- or exactly what radius to grind and how to adjust it to come to focus at just the right point.

I've made an 8" diameter parabolic mirror, it's not really difficult, just a lot of labor/time and some ability to pay attention to detail. Making transmissive lenses is a bit more difficult, but still not so hard that Galileo shied from making his own in the 16th century.

 

[jsmoove]

Surplus shed sent me the info on: https://www.surplusshed.com/pages/item/L10528.html (double convex)
But if the focal length is measured from the middle of the lens, then it wont work....since I'd need a working distance of zero.
Yes haha, an addict and an amateur.
The thing is I'd like to make multiple, not just the one. But I guess if I got really good at glueing lenses together, I could try the half sphere glued on a glass block route.
A ball lens would have worked too, but damn are they expensive. And not alot of surface area to work with

 

[jsmoove]

@Donald Qualls Maybe I have to give up on the idea on a lens all together. If I were to take into consideration of the average mobile phone's minimum focus distance (I think it's like 7-10cm or something) could I just put a 7cm cylinder of glass in front of my phone camera and image the opposite end?

 

[Donald Qualls]

You'd need a longer cylinder than that -- the glass will act shorter optically than air does (light is refracted away from the normal on leaving the glass, making it seem like the object is closer than it is).

 

[jsmoove]

Ah. Thanks for explaining.
What about a rod lens? They seem to have focal lengths, but im confused as to where the focal length is measured from

 

[Donald Qualls]

Ah. Thanks for explaining.
What about a rod lens? They seem to have focal lengths, but im confused as to where the focal length is measured from

Aren't those just a glass rod, used as a cylinder lens? Don't think they'll do what you need...

 

[Nodda Duma]

I think it's very unlikely you'll find any lenses like that. A lens that focuses on its own surface is a very specialized item, and I doubt there have been any made since Stanhope viewers went out of fashion.

You might contact your local telescope making club; I'm pretty sure they'd be very happy to welcome another addict, er, amateur optician to their ranks. There's no question you can make a lens like what you want, and those guys will even be able to give you the formula you need to figure out exactly how much to thin it after you have the curve ground and polished -- or exactly what radius to grind and how to adjust it to come to focus at just the right point.

I've made an 8" diameter parabolic mirror, it's not really difficult, just a lot of labor/time and some ability to pay attention to detail. Making transmissive lenses is a bit more difficult, but still not so hard that Galileo shied from making his own in the 16th century.

I gave him a solution earlier in the thread. It’s not that special. Granted, I’m not an amateur optical designer.

 

[jsmoove]

@Nodda Duma So a ball lens? I just wasn't sure where to find a larger one if I need a high refractive index. Larger 15mm+
Custom then as you said?

 

[jsmoove]

Only because I need more actual physical area for the image I am going to paste on the lens.
Anyways, I realize I've taken this thread way off topic from my original question, I'll see if I can find a ball lens. Thanks to all.

 

[jsmoove]

@Nodda Duma Hey, a question about reverse fresnel lenses....would these essentially work better against a camera phone lens because the camera lens would be looking through the glass before the fresnel, since the fresnel is on the backside of the plano convex as I understand it? Because putting a regular fresnel up to a camera phone wouldnt work unless the grooves were microscopic right?
https://www.knightoptical.com/stock...---reverse-configuration-solar-concentrators/
Because these offer large diameters and short focal lengths....says though "These lenses are not generally used for imaging" so not sure just how terrible the image quality would come out.
I'm not sure if this is what you were referring to a while back when you mentioned to use a fresnel on glass.

 

[jsmoove]

@Nodda Duma Can you clarify the fresnel part of this, is the fresnel at the bottom of the acrylic block or the top?:
"You either need to be looking at a ball lens, or if you don't like that, then select and bond a short focus Fresnel lens masked down to about f/5.6 or even f/11 and bonded to an acrylic block with the same length as the focal length of the Fresnel (accounting for the index of refraction of the acrylic block)."

Because I understood that you couldnt use a fresnel lens in close contact with a phone lens...

 

[AgX]

What is a reverse fresnel lens?

 

[jsmoove]

Sorry, reverse configuration or something. Basically just need a lens with a BFL of 0. As Nodda already told me, a ball lens would do. But he also mentioned a fresnel lens attached to an acrylic block. I was wondering if the fresnel would be at the bottom of the block, since the block is going to be in contact with my phone lens.

 

[Nodda Duma]

I no longer think a fresnel would work as well... I May have made that suggestion when I wasn’t as familiar with what you were doing

 

[jsmoove]

Ok cool. Still haven't found an alternative to a high index ball lens....that is for a single glass lens with a bfl of 0.
Only reason for not biting on a ball lens is the crazy prices for higher diameters.
I was wondering if there was such a thing as something like a convex microscope slide instead of a depression slide.
I looked into microlenses/arrays, they seem to have short back focal lengths, but then the actual surface area would be so minute to image anything.
I found: https://www.illumn.com/ahorton-27-2mm-aspheric-glass-lens.html Which has a bfl of 10. But if I were to add a optical window to it, it would have to be 15mm in thickness, if the optical window had a index of 1.5.

 

[Nodda Duma]

Just find a large round glass ball. They are cheap

 

[jsmoove]

I thought I needed a high index glass ball in order to achieve a 0 bfl/working distance.....as per:https://laser.physics.sunysb.edu/_wise/wise187/2004/reports/kira/index.html
any regular glass ball will do?? I'm confused
I need to be able to focus on the lenses surface itself

 

[jsmoove]

I can use a regular (1.5?) glass sphere and focus on the surface of the sphere itself?
How does that work?
Somehow I missed your czech glass ball link from previous, so any of those would work?

 

[Nodda Duma]

You should go back and read through this thread carefully. No need to rehash territory already covered. In particular, read what I posted at the end of post #12 last year.

 

[jsmoove]

Alright, ill do some tinkering with a 25mm: http://www.glass-sphere.com/en/eshop/kulicky-pro-technicke-a-dekoracni-ucely-10-mm-40-mm.html
And then report back

 

[jsmoove]

....Though I probably don't need a whole kilogram, wow! I'd have to assume a 30mm would work as well as a 25mm.

 

[jsmoove]

Have you ordered with that company before? I'm in Canada and they don't have a Canada option.....though maybe they'll do it for me anyways