SOM Berthiot Eidoscope n°3 275mm f/4.5 This lens is very rare and hard to find especially in this good condition. The lens is clear with no scratches, no fungus and no haze. The external condition is pretty nice and the shutter is working fine and smooth. There are 4 Eidoscope numbered from 1 to 4. This one is number 3. The SOM Berthiot Eidoscope is a soft-focus lens designed to produce images with a controlled blur effect. Here are the key points to remember: Origin and History: The Eidoscope was originally launched by the French firm Hermagis in 1903. SOM Berthiot, founded by Claude Berthiot in 1857, acquired Hermagis in 1934 and continued to produce the Eidoscope. The lens remained in the SOM Berthiot catalog with focal lengths of 275mm, 375mm, and 480mm. Technical Specifications: Initial aperture of f/5, reduced to f/4.5 by SOM Berthiot. Brass construction, then finished in black on an aluminum body. Lens diameter of 6cm and total length of 15cm for a focal length of 275mm. No anti-reflective coating. Use and effects: The Eidoscope produces artistic blur thanks to controlled spherical aberration. The blurring effect diminishes as the aperture closes, allowing for a sharper image. Used for portraits, landscapes, and artistic scenes, the lens offers a soft, enveloping finish. Special features: The Eidoscope's aperture scale differs from modern standards, offering finer steps for greater blur control. The lens allows separate use of the front and rear elements to achieve dual focusing. Value and collection: The Eidoscope is sought after by collectors and museums for its historical value and rarity. Models like the SOM Berthiot Eidoscope sell for significant sums at auction. Examples of use: Used by photographers such as Karl Schenker for female portraits, combining retouching and blurring effects. Used in pictorialist scenes and artistic portraits, often retouched to create specific atmospheres. Photos are part of the description. Secured and insured shipping.