What is the leica summilux m 90mm f 1 5 asph good for?

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From Leica Summilux-M 90mm f/1.5 ASPH: Leica Summilux-M 90mm f/1.5 ASPH: A prime lens by Leica for Full frame cameras, 90mm f/1.5. Specs - Maker: Leica - Focal length: 90mm (prime) - Maximum aperture: f/1.5 - Made for: Full frame sensors - Mounts: Leica M - Stabilised: no - Autofocus: no, manual focus What it frames like - On full frame (Leica M): as marked, 90mm. Cameras it fits - Leica M9: Full frame - Leica M9-P: Full frame - [Leica ...

From Lenses: Aperture: The f-number says how wide the lens opens. Smaller numbers let in more light: f/1.8 lets in about ten times as much light as f/5.6, more than three stops. A wide aperture means faster shutter speeds in dim light and more background blur. Zooms with a constant aperture, like a 24-70mm f/2.8, keep the same exposure throughout the zoom range; cheaper zooms get darker as you zoom in.

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