[que es tu]

Another thing to keep in mind, with memorizing f stops. Just remember two of them, f4 and f 5.6. Then you double every other one (or half going down) so f4, f5.6, f8 (double 4), f11.2 (the actual f stop, double 5.6), f16, f22.4 (rounded to 22), f32 and f45 (actually 44.8, rounded to 45). Going down from f4 gives f2.8 (half of 5.6), f2, f1.4 and then f1 (a very rare bird!).

I remember seeing a Canon f .95 in a photo history book. Is this even possible, or just a gimmick??

[UncleVanya]

I remember seeing a Canon f .95 in a photo history book. Is this even possible, or just a gimmick??

Absolutely. Even F0.7 is out there in the wild. F0.95 is not nearly as hard.

[Just1MoreDave]

I remember seeing a Canon f .95 in a photo history book. Is this even possible, or just a gimmick??

I have one (sort of). It was removed from a TV camera. It doesn't have any focusing and I think its flange distance is not adaptable to K-mount, so I've never used it.

[swanlefitte]

I remember seeing a Canon f .95 in a photo history book. Is this even possible, or just a gimmick??

I would think the camera mount would limit it at some point. A Pentax mount has a 42mm opening. A 300mm lens would need an entrance pupil of 315mm diameter. I can't imagine the opening at the back big enough.

[UncleVanya]

I would think the camera mount would limit it at some point. A Pentax mount has a 42mm opening. A 300mm lens would need an entrance pupil of 315mm diameter. I can't imagine the opening at the back big enough.

True to a point but remember that the entrance pupil size is not directly linked to the physical aperture only. The apparent size can exceed the actual. And the exit size isn’t part of the formula.

[Peanut]

I remember seeing a Canon f .95 in a photo history book. Is this even possible, or just a gimmick??

As I recall this lens was made for the rangefinder camera.

[dudu]

In a circle, the surface is a comma, it's not as simple as a quadrilateral - Lxl. That's why the diaphragm story seems complicated and, in most cases, useless. It is important to know the basic values ​​that double or halve the exposure - 1 stop. These are 1 and 1.4. If you double them, you get the diaphragm string (stops). Ex: 2, 2.8, 4, 5.6, 8, 11, 16, 22, etc. All others are 1: 2 or 1: 3 stop fractions.

[UncleVanya]

As I recall this lens was made for the rangefinder camera.

Correct. There are also tv lens versions converted to Leica M mount and perhaps native m Mount versions. Several mirrorless cameras models has f/0.95 lenses made for them as well.