Petzval lens order

[swmcl]

OK, OK. I have just taken delivery of my first 'Petzval' lens. I don't know if it is one yet ...

After me and the lens had a chat (I had to tap it with a sophisticated lens removal tool because an owner before me had made a couple of very slight dings in the edge where the lens retainer ring comes out) I have discovered something strange.

The order of the pieces is lens, lens spacing ring - from the rear of the lens that is ...

I see some diagrams of these lenses (I'll try to attach one with this mail) and they dont show spacing rings. What they do show is an air gap (but not the diagram I'm attaching)

Given that I can't mount the thing yet because I need to get a hole cut in a lensboard, should I re-assemble in the order lens, spacer lens?

To make matters worse some diagrams (like the one I've attached) show no air gap on the edges of these two elements but with an air gap in between them. This means very different radii for the two glass pieces...

While I'm at it ... I assume I wont be able to see the join in the cemented pair at the other end of the lens ...? It doesn't look like a pair to me but one blob of glass ...

Ah the joys ...

[Steven Tribe]

Everything is as it should be - so far! The design and construction of the rear pair does vary a lot and a spacer ring is usual - and to your advantage in reconstruction after cleaning as regards correct spacing and likelyhood of damage . I have not seen a glass touching glass pair but would guess that type is more likely to have edge splinters etc. There are other lens designs with a pair of meniscii at the rear - so could be have a thumbnail please for our own enlightenment?

[swmcl]

Hi Steven,

I have sought to take some photos and produce a 'sketch' - which for me is a CAD drawing unfortunately. I have made a pdf.

The sketch shows a relatively true situation I believe (I'm asking for confirmation).

The thicker lens which is both concave and convex (the green one) has a smaller radii of curvature on the convex surface (A) and surface (B) is shallower in comparison.
The thin lens (the blue one) is convex (C) and rather flat (D).

The photos show the lens as a whole and in pieces. The retaining ring is the larger of the two rings. The spacing ring is the smaller.

My sketch is my best guess at the correct arrangement. This is NOT what it was when I purchased the lens so someone has fiddled with it before me ...

I would appreciate being told if I'm on the right track ...

I was trying to clean the lens because it has some white material on the edges. I wonder if it is fungus ...

Cheers,

[Jim Galli]

Hi Steven,

I have sought to take some photos and produce a 'sketch' - which for me is a CAD drawing unfortunately. I have made a pdf.

The sketch shows a relatively true situation I believe (I'm asking for confirmation).

The thicker lens which is both concave and convex (the green one) has a smaller radii of curvature on the convex surface (A) and surface (B) is shallower in comparison.
The thin lens (the blue one) is convex (C) and rather flat (D).

The photos show the lens as a whole and in pieces. The retaining ring is the larger of the two rings. The spacing ring is the smaller.

My sketch is my best guess at the correct arrangement. This is NOT what it was when I purchased the lens so someone has fiddled with it before me ...

I would appreciate being told if I'm on the right track ...

I was trying to clean the lens because it has some white material on the edges. I wonder if it is fungus ...

Cheers,

The 2 steeper radii face each other and the thinner glass faces out, ie it's at the very back. Yes, the spacer goes in between the 2 pieces.

[77seriesiii]

here is another picture that may or may not help. I got this from a friend when I was gripping about the crazy focus I was getting from a 250mm petzval. Yes, I wanted to have some really nice fall-off, maybe even a touch of swirl but not something that would cause a seasick reaction. The first few shots w/ this lens are attached as well. A common thing w/ Petzval lens is the moving of the lenses, spacers by owners to get the effect they are searching for. Your best bet is to revert the lens to original specs, learn it and then start shifting it around. None of my Petzvals cells or spacers were in their original placement when I received them. After the first lens and not know what was going on, it is the first thing I check.

In these two shots, the front lens was placed in the rear, the spacer was between the set screw and the glass. Additionally, the flint faced inward and the crown was facing outward...Ok an easier way to view this. Take the picture of the lens arrangement I attached and flip it 180 degrees. So if you like the teddy shots...go for it! :-)

Ymmv.

Erick

[swmcl]

Thanks Jim and Erick,

When the lens board is machined later this week, I hope to finalise the situation.

I can't see myself chopping and changing much. I'll probably set it as it should be and leave it.

In the process I did find something interesting though ...

I partially filled the unscrewed front element arrangement with some bleach. I wanted to see if the white stuff around the edges was fungus. As I was lying the arrangement on its side to allow the bleach to reach right up to the front edge of the lens shade in the clear liquid some numbers became visible. The handwriting of the lead pencil numbers is in an olden day style. I'm no handwriting expert but it took me back to childhood and the Secret Seven and Famous Five stories (that I now read with my children) ...

Other than this there are no distinguishing marks on the lens.

What fun!

[Steven Tribe]

Many old petzvals have numbers and text when the edge is wide enough. The ground glass edge makes a perfect surface. Looks like the maker was organised and did some quality control/matching!. Darlot lenses even have "Darlot" and "Paris" written on them.

[goamules]

You didn't say what make of lens it is, did you? But Darlot, Paris could be what you are seeing, if a Darlot. It looks kinda like one, except I've never seen one with an iris.

[77seriesiii]

That is cool! On one of my unknown petzvals, the initials R.G. an 265 are written in pencil on the edges. Doing a quick test, the 265 is the focus length in mm (appears to be a 10") and the initials, I am guessing, is the Optician who made the glass. I have taken a look in VM an who knows, but it is part of the fun when finding one of those old lens and trace its history. Good luck!

Erick

[swmcl]

Sorry guys if you thought the writing was on the glass edges. Its written on the blackened inside of the lens shade.

I can't get the front glass separated from the housing that's why I just put a little bleach straight onto the front lens surface.

The bleach seems to have made some of the fungus go away though which is nice. The lens is definitely better off for the experience!

I've got a local engineering machinist on the job of boring out a couple of lensboards for me. He was fascinated with the precision and charm of the lenses and was into old telescopes himself.

I've also learned that little backyard machine shops can be your friend. This guy wants to charge something like $30 for the machining of 2 lens boards. The only camera machine shop in town wants to charge $80 'to start the lathe'. The same camera shop refused to undo some lens elements (hence my persuading the lens myself) and was only interested in helping me if I was to book the lens in for a 'full restoration' !! I presume the guy actually doesn't like customers nor does he want people to take an interest in things like this.

In Australia there are beginning to be some really silly attitudes and prices.

Cheers all,