Derogy portrait lens? (Samples inside)

[Math]

So I got an interesting batch of lenses yesterday, including a Lerebours portrait petzval, an 8x10 meniscus lens with washer stops, E Francais RR, two Hermagis lenses and some other small stuff.
Sounds good, but all were in really bad condition when I got them, the Lerebours had malformed / jammed threads that after a while I finally managed to get loose, only to find out an inner lens element is missing, etc.

http://i40.tinypic.com/20urfw3.jpg

One of the interesting lenses was this one: A strange construction where I once again cannot open the rear or front of the lens due to stuck threads, but it seems to be either two or three lens elements of which one perhaps glued together (I can see balsam, but it might also just be dirt on the edges). The front of the lens has a stop to limit the aperture.


http://i41.tinypic.com/jrcvol.jpg


The sleeve that was on the lens says Derogy (No 26421). This is the odd part, the sleeve fits perfectly and has a hole for a rack and pinion system, but the actual lens does not have a track for a rack and pinion system. Could it be a mis-matched sleeve / lens? Considering the rest of the lenses it's not unlikely they do belong together.

http://i44.tinypic.com/muuzy1.jpg

The focal length of the lens is about 12cm / 5 inch, which is rather short. For a moment I thought it might have been assembled wrongly, but the lens throws a lovely image on the groundglass with a sharp center but gentle softening outwards and lightly blooming highlights. Just now I made a quick polaroid (Fuji FC-100, so slightly smaller then 4x5, but it covers 4x5) to get an idea of what the lens can do, and it seems quite decent, i.e. too good for an accidental lens. Aperture is f4. The lens itself cleaned up perfectly, the glass is haze-free besides some specks of dust, so the glow is from the actual lens, not anything else.

http://i44.tinypic.com/2jflqbk.jpg
(Color version here.) (http://i41.tinypic.com/33nkx1e.jpg)

Any clue as to what this is?

[Steven Tribe]

Yet another period Landscape lens. A few were made with a triple, rather than double lens achromat.

[Math]

Yet another period Landscape lens. A few were made with a triple, rather than double lens achromat.
Hey, I figured as much, but what I was mostly wondering if it's an actual Derogy lens, or a mis-matched lens / sleeve? They fit perfectly.

[Math]

Last night I managed to finally unscrew the front ring to reach the glass and washer stop. The washer stop is a single disc and looks like it could be easily replaced by other stops.
The lens is however not two or three elements, but four, in two groups. I've made a quick drawing of what the optical construction is:

http://oi44.tinypic.com/35bw20z.jpg

Does this look familiar to anyone? I haven't tried it without the washer stop but it should be pretty fast.

[goamules]

I have a couple thoughts. First, as you said there is no track on the inner barrel, yet a tangent focus knob was on the outer, I'd say the internal parts are not original to the sleeve. They could be Derogy, or anything else that happened to fit in the Derogy barrel. I'll relate another thought with a story; once I bought a nice "original" Darlot pillbox lens. Being a simple meniscus, I just flipped it over to confirm glass was in the rear, when inspecting at the vendor's table. I was overseas, and put it in my suitcase until I got home. On closer inspection, someone had taken the original meniscus out, and replaced the rear with an air-spaced set from a petzval, that happened to screw in nicely. The lens was useless. When you have a 100 year old lens, which are easy to unscrew and misconfigure, sometimes you get something that isn't correct or original. Of course, if you flip one of the lenses around, it looks like a rapid rectilinear, depending on the curves.

[Steven Tribe]

Check that the 2 cells have exactly the same efl. If not, then they may be front elements from two Petzvals. Then you have alternative landscape meniscii? The combination of these two gives a very low focal length for an RR with this diameter.

[Math]

I have a couple thoughts. First, as you said there is no track on the inner barrel, yet a tangent focus knob was on the outer, I'd say the internal parts are not original to the sleeve. They could be Derogy, or anything else that happened to fit in the Derogy barrel. I'll relate another thought with a story; once I bought a nice "original" Darlot pillbox lens. Being a simple meniscus, I just flipped it over to confirm glass was in the rear, when inspecting at the vendor's table. I was overseas, and put it in my suitcase until I got home. On closer inspection, someone had taken the original meniscus out, and replaced the rear with an air-spaced set from a petzval, that happened to screw in nicely. The lens was useless. When you have a 100 year old lens, which are easy to unscrew and misconfigure, sometimes you get something that isn't correct or original. Of course, if you flip one of the lenses around, it looks like a rapid rectilinear, depending on the curves.

Thanks, that's of course very possible. Did any rack / pinion systems exist on just friction instead of gears / tracks?
I've thought about it being an RR, but what threw me off was the really nice image it made as-is. That and that the curves seem slightly different, the 'flat' part of each group really has no curve at all, or it's really hard to see with the naked eye. It's of course a bit of a guess to see how the two elements are curved on the inside, as they're glued. I tried re-arranging the lens elements to a more standard RR type with the aperture in the middle and it seems to pretty much make the exact same image, same focal length and aperture. Without stop it's about f2.5.

[Math]

Check that the 2 cells have exactly the same efl. If not, then they may be front elements from two Petzvals. Then you have alternative landscape meniscii? The combination of these two gives a very low focal length for an RR with this diameter.

I just checked, and the two groups have the exact same focal length. It seems more then likely now that it's a mis-constructed RR, though it's still quite speedy and short in focal length.

[Steven Tribe]

The achromats in rear landcsape lenses are typically almost plane and the inside of RR achromats (I have just checked 5 assorted makers!) are visually more concave! Derogy did make caskets (without the bayonnet system?) but there would be no sense in providing two identical lens - unless they were used together!

[Math]

The achromats in rear landcsape lenses are typically almost plane and the inside of RR achromats (I have just checked 5 assorted makers!) are visually more concave! Derogy did make caskets (without the bayonnet system?) but there would be no sense in providing two identical lens - unless they were used together!

I checked some RR lenses that I have, and on all I can clearly see the curvature of the glass. On the groups of the 'Derogy' I can't see any curve or it's too slight to notice. I do think it would have to be made out of two groups originally, as there's two spacers whereas otherwise only one would be needed. If it would be from a casket set it would be rather crude, as the actual lenses are not actually mounted in any rims or metal borders, as soon as you remove the front ring that holds it together you have access to the actual glass.

[Steven Tribe]

My conclusion is that it has two "bought or found" achromats with which someone experimented, perhaps many decades ago! Simple achromats have alsways been available commercially - for repairing telescopes, school physics demonstrations etc.
Using just one of these would make a very useful "original type" landscape lens - or you make a stereoscopic pair?

[Math]

Hmm, they seem to fit the tube rather perfectly if they were found. I think I will keep it constructed the way it is right now, as I really really like how it renders the images. It's sharp yet has a good soothing look to it, without distracting too much. :) Thanks for the help!