I'm a lens designer

[Nodda Duma]

The Aero-Ektar...

I actually have two of these lenses. I obtained them with the intention of turning (at least one of) them into an astrophotography rig. Haven't quite done that yet.

One is a Bausch & Lomb 24" f/6 with an imaging area that I estimated at about 1 meter diameter.

The other is a Kodak 12" f/2.5 with the Thorium-doped element which makes my Geiger counter click. That one sits down in a corner of the basement with the thorium element pointed towards the ground. I had one come across my desk once when I worked for the Navy. I asked the master optician --- a cranky old coot who considered polishing a 1/100-wave surface on an 8" mirror "a fun challenge" -- who said that you get more radiation from one flight to Europe at 35,000 feet than you do off that lens in a year....but to not store it underneath my desk chair if I wasn't done having kids.

I happen to have the prescription for the Aero-Ektar so I could certainly look at updating it. The layout is a double Gauss variant with a cemented doublet as the last element. In fact, here is kind of what it looks like:



-Jason

[NickyLai]

Over on APUG I'm finalizing a 165mm f/6.3 lens for 8x10" format that fits on a Copal 1 shutter. It has zero distortion and performance looks really good.

I like this one. Keep it up and inform me when you are ready.

Good luck!
Nicky

[Corran]

I have no idea what that ray diagram or whatever means, but I do wonder, does the radioactive glass give a significant improvement to the lens?

If it's just a double Gauss variation...any improvements you would do? I wonder if it could be pushed to f/2, and with coatings that helped keep the transmission good?

I've had about 10 AE lenses in my hands, most 7" f/2.5 models but also one 12" and also a Harvard College Observatory lens that looked and behaved exactly like the standard 7" f/2.5 Aero Ektar...but wasn't stained and seemed to not have the radioactive elements. I don't have a Geiger counter though so I can't confirm that. That lens went off to a collector interested in the history of the HCO.

[Dan Fromm]

Um, Bryan, f/2 6/4 double Gauss lenses with interesting coverage have been made. Two of them are cult lenses, bring prices that I can't believe. Most buyers seem to be in the far east.

The longest, I think, TTH lenses in the Opic/Series 0 family are the 4"/1.8 (covers at least 6x6) and 4"/2.0 (covers 6x9) TTH Anastigmats made for a couple of British aerial cameras that shot 6x6 on 70 mm film. I have a 4 incher, it isn't compact or light. These days 4"/2 ones bring a couple of thousand dollars. I have no idea how much of that is due to being engraved TTH. I know, medium format, but the prices are interesting.

Dallmeyer made a roughly comparable lens called Super Six in a variety of focal lengths. Super Sixes cover at least their focal length. Ones of interest for LF are the 6"/1.9 and 8"/2.0. I've had a 6 incher, not compact or light. And usable only on a 4x5 Speed Graphic or at low shutter speeds in dim light, in which case a large Packard might be usable with it. I can't imagine how any of us could use an 8 incher. These days longer Super Sixes bring low five figures. I don't know whether similar lenses not engraved Super Six would bring nearly as much.

I've also, now that I think of it, had a 200/2.0 S.F.O.M. that just might have been made by Kinoptic. I've seen one so engraved. Around fifteen pounds and, yes, immense. For 4.5" x 4.5" on 5" roll film. The few I've seen sold, including mine, brought much less than a Super Six would have.

Be careful what you wish for.

[jnantz]

how about a modern "casket set"
for either 4x5 or 8x10 ( or bigger ! ) so someone can
buy ether the whole 7 focal lengths or
a few and whatever they might need down the road.

there are already so many "vintage" ( older than 1970 )
lenses of all sorts of designs on the market that your new ones will have to compete with
some of these lenses are great and cost next to nothing
not sure how you can compete with a 20$ folder ( for its lens )
but a casket sets ! wisner made one years ago and from what i
understand they are prized ...


john

[Nodda Duma]

I have no idea what that ray diagram or whatever means, but I do wonder, does the radioactive glass give a significant improvement to the lens?

If it's just a double Gauss variation...any improvements you would do? I wonder if it could be pushed to f/2, and with coatings that helped keep the transmission good?

I've had about 10 AE lenses in my hands, most 7" f/2.5 models but also one 12" and also a Harvard College Observatory lens that looked and behaved exactly like the standard 7" f/2.5 Aero Ektar...but wasn't stained and seemed to not have the radioactive elements. I don't have a Geiger counter though so I can't confirm that. That lens went off to a collector interested in the history of the HCO.

Ah well first let me describe the ray trace.

1st rule of lens design: Object is always on the left, image is always on the right.

This is a cutaway view of the glass (the lens shapes) with light rays from different field angles tracing through the glass onto the image plane.

If you were to zoom out you would see this:



So you have to imagine that the lenses are wrapped in a barrel (the barrel design always comes after the optics are done).

The blue represents the zero degree field angle.... Note the blue-colored light ray paths are parallel before they enter the lens. That means the lens is focused at infinity (really far away). Refraction bends the ray paths through the lens and they are focused onto the image plane at right.

Other colors represent light rays coming from off-axis field angles. For this particular ray trace, they represent 8.8 degrees and 12.5 degrees off-axis (so a 25 degree total field of view). Those field angles map to 47.3 mm off-axis and 57.9 mm off-axis (or an image circle with diameter 115.8 mm.... optical designers usually talk in half-angles since circular lenses are radially symmetric).

Usually the other information I watch when designing a lens is either the spot diagram (Imagine imaging a point source like a star and seeing how large the resultant blur spot is on the image plane) or the MTF. Besides that the design of the lens is controlled via a merit function...where I enter in parameters which govern the design and then run an optimization algorithm against those parameters. For complex systems the number of parameters can run into the thousands. For this particular example I had to tweak the patented prescription (fyi patents rarely list the real prescription) to provide a meaningful ray trace...in that case I have 231 parameters. Most are automatically generated to control image quality. The rest I manually entered into the list to control focal length, mass, constraints on airgaps and glass thickness. Then of course there is the prescription itself.

This is what the software looks like (still have it opened for the illustrations above):



Software is called ZEMAX and is pretty much the industry standard for lens design software. Code V and OSLO are the two other design packages. They all support both the design optimization, as well as tolerancing, thermal characteristics, stray light analysis, everything needed to design optics.


As for the radioactive glass.. yes it was very good for optical design at the time it was introduced. But there have been new glasses introduced since then as well as advancements in computer-aided design so nobody really misses the thorium-doped glass.

[Nodda Duma]

how about a modern "casket set"
for either 4x5 or 8x10 ( or bigger ! ) so someone can
buy ether the whole 7 focal lengths or
a few and whatever they might need down the road.

there are already so many "vintage" ( older than 1970 )
lenses of all sorts of designs on the market that your new ones will have to compete with
some of these lenses are great and cost next to nothing
not sure how you can compete with a 20$ folder ( for its lens )
but a casket sets ! wisner made one years ago and from what i
understand they are prized ...


john

Well I'm not really competing... as you say you can't compete with a $20 lens. But I'm certain there are things out there which people wish they had but cannot find or afford to buy. There I can probably help. Your suggestion for a casket lens, for example. Or perhaps an update of an old design with new glass and coatings. Whatever you'd like. If I were rich I would just puke out a bunch of optics and say come and get them.. but I'm not so I have to ask what people would like. Like the 165 f/6.3 for 8x10 that people seem interested in.

For me I get the design practice which is fun.

[jp]

Welcome!

I've gotta say if you want to go in headfirst, the 178 aero ektar has quite a cult and people would line up to get a lighter weight version or something that could be more easily shuttered.

I'm wondering what options we might have for grinding and polishing our own lens glass on a small scale; like a small town eye glasses shop or mfg would do 100+ years ago. Or do we have to go big or go home.

[Nodda Duma]

How about some short tutorials on how to set up lens cell spacing for a range of image conjugates, where the aperture should be located for specific lens types, what gives specific lens types their out of focus personalities, modern coatings -vs- older coatings and more.

There are already SO many optics available today, it would be great to get a better understating of what really makes them different and how they work.



Bernice

I think what I could do is post some documents that I wrote long ago as part of the design coursework I took. The class was real interesting because it stepped through the design evolution of camera lenses. So for example I know why the landscape lens works and what it corrects. Same with the Cooke and the Double Gauss. One interesting thing about the Cooke triplet is that you (well, a lens designer) can get to the Cooke triplet design form starting from a Petzval lens by simply increasing the fields that it corrects for and letting the glass types move into each other during optimization. I figured that out recently...before that I kind of viewed the Cooke triplet as a unique offshoot which didn't tie into anything else. But apparently it does, even if Taylor didn't know it at the time.

Oh and I can unequivocally say that the Tessar does not derive from the Cooke. It can be described as such, but it is not considered like that in the design community.

Also.. .a good book to pick up would be "The History of the Photographic Lens" by Rudolph Kingslake. Kingslake is like the lens design world's version of Ansel Adams.

[jnantz]

sounds good !

so while i can't afford it, how about a 8 element casket set
from 6" to 25" that will cover 8x10 and barely corner 11x14
i know it won't be for me cause i am broke ...
but i am sure that there are handfuls of people who would be
chomping at the bit for a modern glass, coated ( maybe not ? )
8 element casket set that has nice coverage...

sorry if my previous post was vague about my wish list ...