However, they may appear to have different depths of field because the speed of transition between in focus and out of focus differs depending on the optical formula of the lens.

All f1.4 lenses of a given focal length will have the same depth of field. This affects one property, and one property only of the lens: the minimum depth of field. So a 50mm f2.0 will have an effective physical aperture of 25mm. Specifically, focal length over physical aperture equals f-stop. This despite a huge diffuse light source – it’s the mark of excellent coatings, and promises a T-stop close to the f-stop.į-stop is the relationship between the physical aperture of the lens – the effective optical diameter, usually limited by the diaphragm – and the focal length. Notice how the front few elements almost disappear – that’s because they’re not reflecting anything. An f0.95 Leica Noctilux is easily ten times more expensive than an f2.5 Leica Summarit, yet it’s only three stops faster. The faster it is, the easier it is to shoot in low light. The faster the better, and the faster the more expensive. F-stop – we all know what that is, right? The size of the hole in the lens that lets light through.

F stop vs t stop