Darlot lens info

[mylek]

Hello,

as i newcomer on wet plate , i read a lot of thread about Petzval lens and i decided to get one so i got one from the famous website. I was aware than it might be a magic lantern but it was correct for me. So farlens is good, around 7 1/2" around F/4.

In most of the pictures i see on the web, the barrel of the Petzval have the same diameter but not on mine and the front lens (46mm) is smaller than the rear one (50mm) and when most of the Petzval's schematic shows lens with the same diameter.
From what i know it might be from 1864,1865 according to the label on it. On both element, it is written "Darlot Paris" and "13".
What do you think? Which lens i should be using to calculate the proper f stop?

Regards!

85035

[Steven Tribe]

The Darlot experts will add later!
I can see B.F & Co on the barrel. B.French of Boston were the big USA retailers who were active much later than 1864/5! By this time, all photographic lenses had Waterhouse slot or irises!
There is a B.F & Co catalogue, including both Darlot and Voigtänder on CCHarrison's website. Antiquecameras.net.
The catalogue is for 1890!
When you look at the section on Darlots portrait lenses, you will see a reference to Projection lenses "on the inner cover" - which appears not to have made it to the website.

[goamules]

Jamin and Darlot made many configurations of lenses, I've seen about a Dozen different Petzval configurations. This one looks a little like the "can type" convertible discussed here: http://www.largeformatphotography.info/forum/showthread.php?78883-Jamin-Darlot-Convertible-quot-Can-Type-quot-vs-Cone-Centralisateur

[mylek]

Thanks!

It seems that at some time a ring was installed inside the barrel about 1/4" wide at the end of the strip with tooths.
Which lens i should use to calculate the f stop value.
How different is it from the standard Petzval?
What is the purpose of the bigger lens the effect of the cone centraliseur?

[goamules]

You should measure the apparent circle of light holding the lens with a ruler against the front. But measure only what you can see light through, not just the glass diameter. The ring in the lens is an early stop, and may come out.

[mylek]

Thanks!

I read so many ways to measure it, thru the front lens, back lens and iris...
On another note, i have a seroco lens (Vesta) 10" f/5. if i measured thru the iris ring or like you said and i ended up with f/6.3 instead of f/5.
Was the Vesta mounted originally in a barrel or with an iris?

[Amedeus]

The Vesta's I have are all with iris.

I believe Garrett indicated you should measure only the section of the front lens you see light through ... he was not talking about the internal iris. If you re-measure your Seroco lens that way, you'll end up with f5 ;-)

[goamules]

Also, some (many) lenses will measure slightly slower than what they were advertised. The internal fixture for the waterhouse stop often slowed them down a bit.

[mylek]

Thanks Garrett!

I measured f/5.6 using your way and f/6.3 if i measured the iris directly.
So i'll used f/5.6 as a start to index some values on the Seroco's barrel since there is none(???).
I can always double check using a meter, it will be closed enough...