Looking for a lens with over-corrected spherical abberation

[Patrik Roseen]

Hello,
I think I might have understood what makes some lenses swirl (like the petzval lenses).
It's probably a combination of over-corrected spherical abberation that should show up as ringed highlights behind the plane of focus and optical vignetting that is quite easily accomplished with a limiting hole in the back of the lens.

most of the lenses I have tested so far seem to have the ringed highlights in front of the plane of focus and that's not what I am after.

Are there any suggestions for lens designs which creates the ringed highlights behind the plane of focus?

[lenser]

I'm not into the science of optics, but I remember from my days as a portrait photographer a trick we used on a filter to break up background highlights. Taking a UV or other plain filter, we cut a lightning shaped piece of electricians tape and laid it over the center area of the filter from side to side. The results were that all highlights in the background were split with a soft but defined jagged shape in the very out of focus center.

I'm wondering if you might not achieve something like this with tiny slices of tape arranged in a concentric pattern around the edge of a filter and maybe in a bout a fourth of the way. Make them random and spread well apart and about the size of a small fingernail clipping and, in the right out of focus situation....maybe, just maybe this will work.

Good luck.

Tim

[Ken Lee]

If you turned the lens around, would that do it ?

[Patrik Roseen]

If you turned the lens around, would that do it ?

Ken, I have tried this but the physics are against me. I have tried a couple of lenses, each with two lens elements, and turned them in every way I could think of and it still does not give me what I am looking for (except for many other strange effects)

Tim, I will try your suggestion but I am not looking at taking light out of the higlights, on the contrary I wish to make them glow and preserve their light.

googling BAD BOKEH seems to indicate a 'Double Gauss' as a lens design to look for.

[lenser]

Patrik.

My idea won't remove any highlights, but will modify them to be less promenent and may create the swirly pattern that you are after. It's just a total guess, but it just might work into something that will be near to your goal.

Tim

[wfwhitaker]

A lens I had which showed indication of over-corrected spherical aberration was the 14" Kern Dagor, version 3. But I don't think that's what you're looking for...

[Jim Galli]

There may only be a dozen people who know if their lens they want to sell is "over corrected for spherical aberation" (I'm not one of the 12) so you're sort of limiting your chances of finding what you want.

A good lens to play with is the triplet Bausch and Lomb projector lens from the 1920's. They're not worth much, and they're simplicity itself. All 3 elements fall out together. You can flip things around backwards and change spacing to your hearts content with very little effort. I listed a 12" a while back with no takers at 40 bucks.

[Patrik Roseen]

There may only be a dozen people who know if their lens they want to sell is "over corrected for spherical aberation" (I'm not one of the 12) so you're sort of limiting your chances of finding what you want.

A good lens to play with is the triplet Bausch and Lomb projector lens from the 1920's. They're not worth much, and they're simplicity itself. All 3 elements fall out together. You can flip things around backwards and change spacing to your hearts content with very little effort. I listed a 12" a while back with no takers at 40 bucks.

Jim, I was mainly asking for advice in which lens (vendor/lens design) to look for. The double gauss design I mentioned is apparently very complex.Seems most cheap/normal lenses include positive elements whereas the over-corrected lenses include negative elements that will push the spherical abberation to the other side of the plane of focus. That is probably the reason for me not getting anywhere by turning the glass around., they are still positive.

Jim, Does the B&L lens you mention include any negative elements? If you still have the 12" for sale you may send me a PM.

As for knowing if the lens is overcorrected or not I agree that most people do not know (I was not even aware there were such things until Ole Tjugen informed me less than 24 hours ago.

Let me repeat myself in the appreciation for Domenico Foschi's photograph of the boy on the bridge which clearly shows the ringed highlights in the swirling background. That is what I am looking for.
http://www.dfoschisite.com/html/~stock_I.htm view the second photo in the 'Stock I' portfolio (BEAUTIFUL!)

[Jim Galli]

It is 3 elements 3 groups. A classic Cooke triplet. The middle element is a double negative. Front and back are positive.

Actually the double gauss design in one of it's forms is borrowed for the dialyt lens and they are common as dirt. Contact me at jimgalli at lnett dot com. I still have the projector lens and also an interesting old brass dialyt. There are many dialyt's. Goerz Celor, Syntor, Dogmar, Artar, to name just a few. Cooke Aviar is one of the finer dialyt's. Many of the cheap lenses of the 1920's were f6.8 dialyt types. The better ones for your purpose would be the more expensive f4.5 versions. More aperture, less corrections. The inherent problem with this design was flare. 8 count em 8 air - glass surfaces that each lose about 4% of the image forming light. They were sharper than anything else but the flare killed them until after WWII when coated surfaces made dialyt's cake and eat it too.

[Jim Galli]

I went and looked at Domenico's picture. Classic Petzval. That's all you need to know.