XF56 f1.2 released and specs

Started 6 months ago | Discussions thread
Krich13
Regular MemberPosts: 381
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Re: XF56 f1.2 released and specs
In reply to nalax, 6 months ago

nalax wrote:

Let us know how much to change for our 4x5 or 8x10 cameras. Would a banquet camera require more of your "proper" exposure? How about one of Maxwell Smart's spy cameras? Exposure is exposure, buddy.

I hope to see more of the 56mm, hopefully soon!

Krich13 wrote:

ISO must remain the same for the the comparison.

Huh? Why is that? For proper comparison ISO of the FF should be icnreased (compared to APS-C) by a stop and a little, and aperture set to its DOF-equivalent value. Shutter speed the same.

You really don't understand. For film, yes, you need exposure per unit area. For semiconductor sensors the relevant parameter is total amount of light captured by the entire sensor.

Especially for you, I copy my post over again:

________________________________________________________________________

Depends how you define "exposure". In the old film days, it was indeed "exposure PER UNIT AREA" regardless of frame size. Deliver too few photons, and the film is underexposed, milky what not. Deliver too many, chemical changes facilitate turning the entire frame black.

For semiconductor sensors what matters is the total number of photons per photosite, pretty much regardless of the site area. Make two sensors: say an APS-S and FF ones both of say 16 megapixels. Expose them using the same scene for the same duration using 56/1.2 and 85/1.8 lenses respectively. Each photosite will receive the same NUMBER of photons (the number per unit area is 2.25 times larger in the first case, but the area itself is smaller by the same factor). Each photosite (given equal quantum efficiency) will produce the same number of electron-hole pairs (photocurrrent) ergo the same signal and the same shot noise. If you read each sensor with the same preamplifier, equal Read noise will be introduced in both cases, as would be required amplifier gain!

However, a Photomertist would assign the first case say ISO 100, and the second -- ISO 225 based on exposure PER UNIT AREA, even though the physical amplifier gain is exactly the same in both cases.

The origin of your confusion is extrapolation of ISO sensitivity concept to modern sensors -- irrelevant one for digital sensors, the proper metric would be "light delivered to the whole sensor")

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