Darlot Cone rear elements position

[tuant]

I have 4 Darlot CC lenses on hand (well, one is G&CH as you know). All but one had the rear elements in the right order when they arrive. It seems when many of the owners in the past took the lenses apart, they often put the rear elements back incorrectly. Checking with Dan's post, Darlot CC should have the flat side of the flint glass facing backwards followed by the spacer and then the crown with the convex side towards the front group (assuming Dan's chart is correct:-). I guess part of the problem is that the lens will still focus even when the back elements are in wrong position (They can be put together in 4 different ways). I was finally able to take apart my G&CH and it was in wrong position as well, even though it looked like nobody had touched it in at least 100 years. I even made a plate with the elements in wrong order and the plate came out nicely. I wonder if anyone else had encountered the same problem in the past.

Also, all my Darlot CC have Darlot or Jamin written on every glass but the G&CH only had two sets of numbers. The numbers on the front and back crowns match. I don't think Darlot had anything to do with it. This must be G&Ch's work.

[tuant]

Forgot to attched Dan's chart.

[tuant]

This illustration is a little confusing by itself: the crown on top of the spacer should be much thicker with the convex on the top side. In the picture it is almost flat. That's probably why two of my lenses came with the flat side of the flint on top instead. The problem is that it will still focus:-)

[CCHarrison]

These may help....


http://www.pacificrimcamera.com/milanpub/CCTutor/cce1/FrameSet.htm

http://www.pacificrimcamera.com/milanpub/CCTutor/cce2/FrameSet.htm

Dan

[goamules]

Tuant, there are two correct configurations for a petzval's rear glass, depending on manufacturer and year. The first is the the way Professor J. Petzval patented it, with the flat side of the thinner glass facing the rear (ground glass). The second was the way Dallmeyer patented it in 1866, which reversed both rear lenses so that the thinner was facing forward, flat side out. His patent also included the mechanism to change the air spacing between them. In either method, the more radical curved radii are "nested" together, separated by the metal ring. Jamin/Darlot followed the traditional J. Petzval method. Dallmeyer did it their way after 1866. I guess we could dare to say the Dallmeyers made after 1866 are not really Petzvals.

[tuant]

These may help....

Thanks, Dan! I have never taken the pillbox off in portrait mode (with no water house attached). I will try the off mode to see how much DOF will be lost.

Dan


Tuant, there are two correct configurations for a petzval's rear glass, depending on manufacturer and year. The first is the the way Professor J. Petzval patented it, with the flat side of the thinner glass facing the ground glass. The second was the way Dallmeyer patented it in 1866, which reversed both rear lenses so that the thinner was facing forward, flat side out. His patent also included the mechanism to change the air spacing between them. In either method, the more radical curved radii are "nested" together, separated by the metal ring. Jamin/Darlot followed the traditional J. Petzval method. Dallmeyer did it their way after 1866. I guess we could say the Dallmeyers made after 1866 are not really petzvals. There's some blaspheme for you.

Hi Garrett,

This is really good to know! You are saying both ways are correct. My first lens had the crown in the rear with the convex side towards GG, I have always thought that was the way. When I got my second lens, the rear was flat, I thouht that must be incorrect. I will check on my GG to see if there is any difference between the two. With Darlot CC, I guess you can increase the space between the two cells by adding another ring, you just don't screw in as much. Haven't tried that. I might experiment today.

Tuant

[tuant]

Does anyone have any good advise for edge separation? On one of my lenses, there is about half CM of yellowish ring all around the front cell. For portrait it should be ok, paysage mode might suffer around the edge. I have not tried any plates yet.

[goamules]

...

[tuant]

That picture is not a petzval, so I'm not sure what types of glass it would be.

Yes, Garrett, it was my mistake, the thicker one is the flint, Dan's Petzval article has that clearly illustrated. Thanks for the trouble! I deleted the post before seeing your answer. The question now is what is Darlot's original set up, with the crown on top or at the bottom, does anyone know for sure? From the GG, I couldn't see any difference.

Tuant