XF56 f1.2 released and specs

Started Jan 6, 2014 | Discussions thread
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Erik Magnuson
Erik Magnuson Forum Pro • Posts: 12,237
Re: XF56 f1.2 released and specs

viking79 wrote:

Robert Garcia NYC wrote:

not really your not factoring in the extra real estate on the sensor, which is gathering light. So, it's an f 1.8.

No, f/stop and focal length are physical properties of the lens that never change on any sensor size

Yes, but since the "f" in f-stop means focal length, you cannot convert one for comparison without converting the other. Basic algebra. This also more correctly represents the lens size and difficulty in building  which is why a 1" sensor can have an affordable 10x constant f/2.8 zoom.

However, the larger sensor catches more total light, hence the term equivalent. This lens is about equivalent to an 85mm f/1.8 used on full frame.

It will also have essentially the same DOF characteristic as 85mm f/1.8 on FF.

Amount of light available for autofocus on the 56mm f/1.2 will in fact be greater.

This is tricky - are the AF sensors scaled to sensor area or fixed size? If they are PDAF sensors, then they look through a smaller virtual aperture of the lens and the extra speed doesn't help.

The downside with large sensors is you start to get very dim viewfinders. Look at old view cameras, very little light to focus with.

There are two issues:

  1. Getting all of the light collected to the eye while shielding from ambient. If you had a giant hoodman-type loupe for a view camera, it would seem brighter
  2. The ground glass for such cameras was optimized to show focus variation and not for light transmission. Even among 24x36mm camera viewfinders, you had significant variations in brightness depending on the focusing screen design. Since most cameras also metered off the screen, you often had to adjust your exposure when swapping focus screens.
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