Possibly moving to full-frame mirrorless from m4/3’s

Started Nov 21, 2020 | Discussions thread
ZapperVT Senior Member • Posts: 1,441
Re: Two quick and easy reasons

abera wrote:

ZapperVT wrote:

avalvo wrote:

- Yes, lenses on FF are getting smaller. But, that is only if you are comparing the slower FF lenses, say a 50mm 1.8 to say a 25mm Oly 1.2. They are about the same size, but the Oly is still a faster lens and can be shot at 1.2.

f/1.2 in M43 is equivalent to f/2.4 on FF. Or, f/1.8 on FF is equivalent to f/0.9 on M43. Functionally, the FF f/1.8 has a one stop advantage over the M43 f/1.2.

If you shoot with at 25mm f/1.2 on M43 FF and 50mm f/2.4 , with the same shutter speed and two stops faster ISO on FF, you will have images that are very close in field of view, depth of field, motion blur, and image quality. This is because for the same f number, the diameter of the entrance pupil scales with the crop factor. It is twice as big for full frame, letting in 4 times as much light at the same f number. If you go to f/1.8 on FF, you have an image with a depth of field one stop smaller and an IQ potentially one stop higher than possible with f/1.2 on M43.

You may object that in terms of exposure, f/1.2 is still f/1.2, and you would have to use a slower shutter speed or higher ISO on the FF f/1.8 lens to get the same exposure wide open.

ISO is not an exposure parameter - it's actually defined by using the exposure parameters so it would be a circular definition. In photography, exposure is the amount of light per unit area (the image plane illuminance times the exposure time) reaching a frame of photographic film or the surface of an electronic image sensor, as determined by shutter speed, lens aperture, and scene luminance.

Also, if one shoots raw, there isn't really need to use higher ISO - they can be be benefits (less read noise), but also drawbacks (lower saturation point).

Other than this, you're correct.

I agree with your statement that "ISO is not an exposure parameter". It's correct if a bit pedantic. I meant "exposure" in the common sense - that the exposure meter in camera is indicating the correct exposure.  Which is technically not just "exposure", agreed.  It also takes into account how much the camera will boost the signal from the sensor, either by analog or digital means, and how it will render jpegs if applicable, before writing the data to the file.

This is what I meant: If you shoot a FF at M43 equivalency, with same shutter speed, twice the focal length, twice the f number, and two stops higher in ISO setting, both the FF and M43 exposure meters should be about the same, and the resulting jpegs will have similar lightness.  (Given that different models and makes differ in metering and jpeg rendition.)  I think that's how "exposure" is commonly used.

That is part of the equivalency. If you shoot at the same shutter speed and wide open with both lenses, you will have to increase the ISO by 1 stop on FF to get the correct exposure.

Nope, ISO is not an exposure parameter - it influences the lightness of the output image if one shoots JPEGs, as well as usually has influence in noise and max signal capacity.

yes, in other words, the jpegs will have similar lightness.  Commonly, if incorrectly, referred to as exposure.

But a FF sensor has a two stop advantage in noise vs IQ, so you still end up with a 1 stop advantage in IQ on the FF system.

Noise advantage is (almost entirely) a function of collecting more light - either by using a larger aperture diameter, longer exposure, or changing the ambien light (e.g. flash light). In practise this means that FF has more potential, but in some cases it can't be used - for example limited available light situation with deep DoF and fast exposure requirement.

Agreed.  Same DOF means 2x the focal length and 2x higher f number for FF compared to M43.  That means the same size entrance pupil, the same amount of light, and the same noise.  More generally, any form factor that meets the photographic constraints will yield similar results with equivalent settings.  But some systems will have regions of operation that others can't reach with available equipment.

Source: Here's an article on equivalency by one expert.

I recall that back in the film days ISO was actually a standard, relating the optical density of the exposed film to a given light intensity.  But now in digital photography ISO is not well defined.

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