Just have a look at the beautiful engravings…
“demi-grand-angles avec rotateurs”.
This is an extremely nice piece off engineering.
By turning the lens hood you can change the aparture which is build inside the lens.
This mechanism is made of 2 brass tubes slided into each other.
They have a fitting which makes it impossible to put even a human hair between them.
Just have a look at the lens design. perfectly round and polished by hand
I contacted Geoffry Berliner about this lens,
You really should have a look at their webiste.
I want such a daylight studio......
It's on my wish list to visit once.
He has send me the following information about this Hermagis:
"It is a Schnitzer / Harrison Globe formula from the 1862 patent.
This formula was licensed out to European manufactures of the period as it was
too expensive to export due to tariffs and import fees.
The Emil Busch Pantoscop is in the same category as your Hermagis.
A great find of a very rare and beautiful lens."