DIY Meniscus

SteveH · Jul 28, 2006

All,
Anyone try their hand at making a meniscus lens ? Judging by the prices that the vintage ones have been going for, the considering that I want some abreviations anyway, I might give it a shot.
Im not sure if Im going to just get a single element, or an an achromat. Thoughts on this ?

I've been moving a large hunk of brass around my workbench for over a year, so perhaps this would be a novel application for it. Im looking for something in the 210-300mm range; which I've been able to find lenses quite easily (coated even !) for under $10. These have been around 60mm in diameter. Im not sure if Im going to try my hand at making a revolving aperture wheel, or if I will make some discs (ala imagon).

One design element that I am not sure of is where to place the aperture ? I THINK it should be spaced 1/2 the focal distance infront of the lens; does that sound right ? Also, would there be any way to figure out coverage before I construct the lens ? I want it to cover 4x5, but at the moment Im just looking for the largest glass I can find, and hoping for the best.

Thanks !

Terence · Jul 28, 2006

The book Primitive Photography by Alan Greene goes into making some very simple lens based on 19th century methods, including a simple meniscus lens and a classic landscape lens, and including rules of thumb for coverage, stop placement, etc. If I remember right, the achromat seems the way to go as you don't have to adjust after focusing to allow for the difference between "optical focus" and "chemical focus." This may depend on the light sensitivity of the emulsion you're using, though.

SteveH · Jul 31, 2006

Terence,
Great, thanks for your help. Im going to see if I can get a copy of that book, and take it from there.

Regards,

Jim Jones · Jul 31, 2006

The meniscus lens used in many box cameras has the convex surface towards the film and the aperture maybe 1/6 focal length in front of the lens for best performance. Sometimes, to make the camera more compact, the lens has its concave surface towards the film and the aperture behind the lens. This gives a shorter length to the camera, but has more curvature of field. A google search for landscape lens pointed to a couple of downloadable lens designers. I have no experience with either.

OSLO-EDU from Sinclair Optics OSLO-EDU

CODE V from Oprical Research Associates CODE V

SteveH · Jul 31, 2006

Jim,
Excellent ! OSLO-EDU has a linux version ! Im going to mess with this when I return home later this evening.

Terence · Jul 31, 2006

Oslo is a nifty program, but I haven't had much luck with it. I'm fairly dependent on what lens are available from Surplusshed.com, Anchor Optical (Edmund Scientific), etc.

The landscape lens in the Greene book has the concave side towards the subject. Although much simpler, it looks very similar to the old Darlot landscape lenses, with a small (to my eye) stop at the front of the barrel to cut down on some of the distortion.

There's one historic photo in the book, I believe taken with a landscape lens, that has the Galli-esque swirly bokeh, and the most amazing look to the in-focus areas. The in-focus areas almost look 3-D, but also make the subjects look like a little diroama. the combination of distortion, bokeh and depth-of-field is what I've been trying to replicate, unsuccessfully.

tomf24 · Jul 31, 2006

For a non technical DIY type approach to making simple lenses.... take a look at the on-line reprint of my friend's View Camera article

http://www.siskinphoto.com/magazine/zpdf/LensAssembly.pdf

Nathan Smith · Jul 31, 2006

Terence said:
... that has the Galli-esque swirly bokeh ...

There you go Jim, when your name becomes a new word you know you have truly made it!

Nathan

SteveH · Jul 31, 2006

All,
Thanks again for the info...It looks as if I really need to get a copy of that book. As far as the lenses go, I will be doing all of my purchasing from surplus shed as well, so in a way the lens design software is a moot point; but then again if I can get the specs on the glass, I can at least see what it is theoritically able to do.
The only issue that Im really worried about is coverage. Any thoughts on this ? Im just going out and buying the largest lenses I can find that are in my desired focal range (surplusshed has about 10 lenses that should work, coated too !).

Tom- interesting article, thanks for the link

Terence · Jul 31, 2006

The irony is that both of the lenses I've bought from Jim are very sharp G-Clarons. My brass cannons have been from other sources.

I'm still trying to figure out how I can make/adapt something to use with my 28" focal length, brass, portrait lens. A head-shot on 8x10 would require more than three feet of extension. Living in a 750 SF apartment, that would take up half my living room.

Actually, my favorite swirly bokeh photo is still Kerik's girl surrounded by trees, but I gave Jim the hat-tip as he has been such a promoter of the look.

Terence · Jul 31, 2006

The Greene book has some rough estimates of coverage for a given type of lens based on the diameter and focal length. If I remember, I'll bring the book in and scan a couple of pages for you.

SteveH · Jul 31, 2006

Terence,
Great, thanks. The lenses I am looking at are 50mm dia/250mm FL, and 60mm dia/235mm FL.

removed account4 · Jul 31, 2006

hi stephen

you might look for an article that john siskin wrote for view camera a few years back. it was all about what you want to do. he got his lens optics from anchor optical ( i think?) and he was using a tin can as a barrel ...

i can't remember when it was -- 2 maybe 3 years back ... if i can dig it up i'll make a copy for you and send it your way ...

john

Mark Fisher · Jul 31, 2006

If you want to stretch a little, you could do a compound symmetrical. I just finished one this weekend (I used a modified version of the method from Primitive Photography). A few dollars in PVC pipe, black paint plus about $10 in lenses (2l enses, 50mm dia and about 500mm focal length) from Anchor Optical. The end focal length should be around 250mm. These lenses are scratched, but I suspect that won't matter too much. I'll write up something once I am done with the experiment (I also have about a 2 Lb 8x10 camera to go with it!).

Mark

SteveH · Jul 31, 2006

Mark,
I look forward to seeing your report. I want a meniscus for the look, as I really am going for a portrait type of lens.
I drew up some plans this afternoon real quick, and will toss them into CAD later. Being as I ordered two sets of lenses with different diameters, I figure I will make the barrel to fit the larger lens, then I can set the smaller diameter lens in a thicker bushing to thread into the barrel. Also, I can just make another aperture wheel (for the other focal length) to fit the same barrel. This will save me from making two barrels, being as large pieces of brass aren't cheap.
On the original oldies, how did they seal the area between the aperture wheel and the barrel ? Is it just a tight tolerance, or did they put a piece of felt, etc to seal it ?

SteveH · Jul 31, 2006

All,
Here's a quick drawing I came up with earlier. My dxf-jpg converter sucks, so I have two drawings here (its hard to see the plan w/dimensions in black/white only).
As it sits now, its setup as a 235mm f/5. Im not sure if Im going to put in a wheel type of aperture change, or if I can make some 'thimble' type of stops that would insert into the barrel (ala Imagon). I need to take a look at some designs that use a rotary type of stop, as Im not quite sure 'how it works' yet.

Dan Fromm · Jul 31, 2006

Meniscus? Looks bi-convex to me. Please clarify. Do you mean "single element" when you type meniscus?

Markok765 · Jul 31, 2006

isnt meniscus the same as in disposble cameras?

Terence · Jul 31, 2006

Greene suggests using :
[A] A focal length equal to 0.828 x Film Diagonal.
A lens diameter equal to 1/5 to 1/7 of the focal length.
[C] A stop of between f/16 and f/32, located 1/6 to 1/7 of the focal length in front of the lens.

SteveH · Jul 31, 2006

Dan Fromm said:
Meniscus? Looks bi-convex to me. Please clarify. Do you mean "single element" when you type meniscus?

Dan,
We're both right I believe. A meniscus can be either singular, or achromatic. Either way, I have seen the doublet called a 'meniscus' in various texts.
I would have been more specific in my title, but when I wrote the first post, I was not sure if I wanted to go with an achromat or not.

TERENCE said:
If I remember right, the achromat seems the way to go as you don't have to adjust after focusing to allow for the difference between "optical focus" and "chemical focus."

I looked more into that, and decided that it was the way to go.

SteveH · Jul 31, 2006

Terence said:
Greene suggests using :
[A] A focal length equal to 0.828 x Film Diagonal.
A lens diameter equal to 1/5 to 1/7 of the focal length.
[C] A stop of between f/16 and f/32, located 1/6 to 1/7 of the focal length in front of the lens.

Thanks for looking that up for me. I take it that the [A] calculation was for minimum coverage ? If so, then the widest lens would be a FL=135mm, and 22.5mm in diameter to cover 4x5. Hopefully this is the case, as I am well within the guidelines with a FL=235mm, and a dia of 60mm.
As far as the stop placement, would this be true of all focal lengths, or just the minimum coverage lens ?

Thanks again.

Dan Fromm · Aug 1, 2006

SteveH said:
Dan,
We're both right I believe. A meniscus can be either singular, or achromatic. Either way, I have seen the doublet called a 'meniscus' in various texts.<snip>

Thanks for the reply.

I think you're mistaken. Per my dictionary, a meniscus lens is a concavo-convex lens. Not bi-convex. Shape matters ... And so do names.

SteveH · Aug 1, 2006

Dan,
Thanks, I agree completely with you now. I was confused by the wording of old lenses, and looking at diagrams of the imagon.
The major reason why I stuck with the thought was from reading this @ the LF board

Ernest Purdum said:
"Meniscus" refers to the lenses shape, so it can be one piece of glass with considerable chromatic aberration (simple meniscus), or can be color corrected by using an additional element (achromatic meniscus). When P&S used the term "semi-achromat", I'd guess they were saying that the designer purposefully left some chromatic aberration uncorrected. Gundlach, on the other hand, presumably corrected the chromatic aberration as much as possible.

So, I incorrectly put 2 and 2 together. When I saw the diagram of an imagon (which I thought to be considered a meniscus lens), I saw the doublet and figured the concave lens to be the additional element that Mr. Purdum was refering to. I now see that a 'true' achromatic meniscus is actually 3 lenses.

Thanks again

Terence · Aug 1, 2006

It was based on rough guidelines he pulled from early photography texts. It allows for a fairly conservative 45 degree angle of view. A longer lens would be better corrected as you'd be using more of the central area of the image circle.

The stop placement remains the same, at least for slightly wide and slightly long lenses.

I have to go back and look. After a good night's sleep it seems like it should be FL/0.828, which would give 196mm for 4x5. I remember thinking it was slightly longer than normal "normal". Not that it matters as you already have a lens picked out, but this would make yours only slightly "long".

SteveH · Aug 1, 2006

Terence,
Ok, that's fine, thanks. I just wanted to make sure that the guidelines he layed out were for minimum coverage.

DIY Meniscus

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