This is a fine example of an early French Grand Angulaire lens with an image angle of 90°.
As was common during this era, this lens lacks engraving on the outside, but comparing its dimensions and the barrel layout, it can be confidently dated to 1880-90 to the Derogy workshop. I found ads for this lens in the 1890 Derogy catalog below.
This masterpiece of optical engineering on this lens is still impressive today.
The brass is very nice, and this lens shows its authentic golden patina. The glass is also in great condition, showing only the occasional cleaning marks and tiny specs.
The lens offers a 90° angle and thus a very large image circle, making it one of the very few ultra large wide angle lenses that remained.
The lens comes with a revolving aperture, which works perfectly. It has apertures from F/11 to F/44 in the following increments (F/11, F/16, F/22, F32, F44). With its 90° imaging angle, it has an image circle of about 400mm wide open, enough to cover 8×10 and maybe even the 12×12 format and beyond.
I measured the front element of this lens, and it is 39mm. I also verified the focal length to be 7 inches (180mm). Knowing these two variables makes it easy to calculate and confirm the widest aperture on this lens. Take 180 / 11 = 16. I am taking the focal length of 180mm and dividing it by the published aperture of f/11 to calculate the diameter of that f/stop (16mm). As expected, I measured the f/11 aperture diameter on this lens, which was 16mm. By approaching this in the way I laid out, I can confirm the widest aperture of this lens and work with confidence.
My lens has its original fitting flange and the original leather lens cap!
BAISC LENS SPECIFICATIONS
Height: 5cm
Width: 5cm
Weight: 250gr
