Single element lens design questions...

[Dr Klaus Schmitt]

It can deliver quite interesting results...





(both shot on digital in Nancy France / Place Stanislas )

[papah]

Beautiful, Klaus!

Details on the lens you used?

[Dr Klaus Schmitt]

Simple quartz singlet, mounted into old enlarger lens barrel I had laying around.

works also nicely for closeups:

[desertrat]

Those are great shots! BTW, the biggest problem with surplus lenses, even meniscus lenses, is that the curvatures aren't strong enough to flatten the field. Therefore, most of these lenses suffer badly from curvature of field. This is where most of the softness at the edge of the field comes from, far more so than the other aberrations. The Wollaston meniscus is what you want. The lens curvatures are optimized to give a (fairly) flat field for a normal focal lens. This is what most of the old box cameras used. The lens curvatures follow a certain ratio to give the desired focal length, but I haven't been able to find out what that ratio is yet. My google-fu isn't so great.

You can download for free a lens design program that's used by amateur telescope makers called OSLO.edu:

http://www.lambdares.com/education/oslo_edu

Warning, this is an extremely complicated program, with a steep learning curve. In a couple of years of my spare time I may succeed in learning how to use it properly.

[desertrat]

OK, I was able to find some design information for the Wollaston landscape lens at the following link:

http://books.google.com/books?id=acr...ed=0CCAQ6AEwAw

Scroll down a couple of pages for a discussion of the design and the lens prescription. The lens is tiny, having a focal length of one inch, but it should be able to be scaled up to any focal length by multiplying the radii and thickness by the same constant. I suggest multiplying by 13 to 15. This will give a slightly longer focal length than is customary for 8X10, but the edges of the field will probably look a little better.

[desertrat]

I made a mistake on the focal length of the Wollaston lens in the previous post. It's not one inch, it's one in whatever system of measurements you want to use. I caught this re-reading the article and checking some other sources I have on optics. This lens' focal length can be one inch, centimeter, foot, meter, furlong, etc. That means you should be able to scale it to any focal length you want.

[Dr Klaus Schmitt]

Well, I was happy about that curvature, as I achieved what I wanted, to have the outer parts of my images appear (much) more unsharp that the inner parts ... depends what one wants and what for. I have experimented to use a concave element in front or behind which acts as a field flattener - works quite well. Piazzy Smyth once invented that.

[desertrat]

Now that I think about it, the OP probably wanted the same effect. I'm not aware of any Wollaston formula lenses available to purchase, so one would have to make the lens.

Some amateur astronomers grind and polish their own objective mirrors, and a few of them make their own lenses for special purposes. This isn't a beginner's project, but I understand the equipment required can be built in a home workshop. A small lathe is usually needed to make some of the measuring instruments, like the spherometer. Ihave seen plans for a spherometer that doesn't require a lathe to build.

[papah]

I can just see it now...

Aspheric hand lens grinding at home, in pursuit of the perfect "Pinkham & Smith" look.

The analog equivalent of writing Photoshop plug-ins to mimic pictorialist soft-focus.

Count me in!

[Maris Rusis]

Single element meniscus lenses are widely available: spectacle lenses! My optometrist sells me 75mm diameter spectacle blanks in a variety of powers for $20ea. The latest on my 8x10 camera is a 2.5D (400mm F.L.) in CR39 plastic that works a treat.