XF56 f1.2 released and specs

Started 9 months ago | Discussions thread
Krich13
Regular MemberPosts: 438
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Re: XF56 f1.2 released and specs
In reply to malcolml1, 9 months ago

malcolml1 wrote:

Now I've thought a bit more, I think there is another source of confusion....I have convinced myself again that, whilst I accept that noise levels would be different, if I took a photo with my Fuji and the 56/1.2 at ISO200 and did the same with my (now sold) 5D mk2 with the 85/1.2 at ISO 200, both in aperture priority mode, they would both select much the same shutter speed (I assumed that both Canon and Fuji agree on definition of ISO).

At the same ISO, yes. But why would you select the same ISO in the first place?If your shot requires (for your artistic or technical purposes) certain DOF, or certain shutter speed, or certain noise level -- you are free to play with remaining parameters at will.

In case of equivalent apertures (say f/1.2 on APS-C and f/1.8 on FF) selecting ISO 1 1/3 stops higher for an FF would result in the _same_ DOF, noise and shutter speed. The only reason to avoid raising the ISO are either noise concerns (not a concern, the noise is the same in both  cases) or shutter speed (say if you want to avoid to fast a shutter to allow some motion blur) -- again not a concern for the shutter speed is the same in both cases.

But then the actual number of electron-hole pairs is not used to form the image - rather the signal is digitized when it is read. If both the APS and FF sensor are 14 bit, then in underlying analog signal is converted into one of 2 ** 14 levels. Further, I assume that the levels (at base ISO or amplification) are spread (non-linearly, I know) between 0 and 'full' (max electron-hole pair capacity for that pixel).

I am not sure what you are trying to say here. Let's consider the example of the same pixel count again. FF photosites 2.25 times bigger. Apertures 1.2 and 1.8 for APS-C and FF respectively. Same illumination of the scene, same shutter speed.

Result: Same number of electron-hole pairs in both cases -- ergo the same signal and shot noise levels. The same amplifier gain is required (though the ISO convention would assign 1 1/3 stop higher ISO rating to the FF case -- but the amplifier and analog-to-digital converters do not know anything about ISO convention -- nor would they care if they did).

At what point of recording, reading or digitization process would the results (signal, noise, bit resolution, dynamic range -- whatever comes to your mind) become any different in these two cases?

To me, a given exposure would result in of the same output level regardless of sensor format - I think this is because the supposedly common definition of ISO.

I really don't understand this passage. Electronics knows nothing about ISO, and any sane manufacturer would squeeze as much signal-to-noise ratio as possible at every setting, whether it is base ISO, elevated or however it's defined. ISO is an empty number assigned to real settings (such as amplifier gain) afterwards.

The advantage of a larger pixel size is the confidence level you have in the level you measure after conversion. More exactly (I work with statistics...),

Great. If you work with statistics you know what Shot noise is, and why it's the same in both cases.

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