Why not a 12-35 F1.8 - F2.8?

Started Apr 2, 2014 | Discussions thread
Klarno Veteran Member • Posts: 4,148
How equivalency works.

JeanPierre Martel wrote:

Anders W wrote:

superstar905 wrote:

You are probably right. Can you explain in simple terms, or perhaps point me to a resource?

The fact that a 12-35/1.8-2.8 for MFT is equivalent to a 24-70/3.5-5.6 on FF with regard to total light on the sensor, DoF, and diffraction

In the XIXth Century, big Daguerreotypes needed long exposure time in order to collect enough light.

Even taking account the influence of the total amount of light on the picture noise, most of m4/3 users couldn't care less that the big FF sensors need more light than m4/3 sensor because they are bigger. That's their problem.

What we care about is the amount of light per mm2 on our sensor: a 12-35mm F/1,8-2,8 m4/3 lens will take a picture exactly as bright as a 24-70mm F/1,8-2,8 FF lens (not F/3,3-5,6). The angle of view and the brightness of the picture will be the same.

If you want to capture a radio signal, a bigger antenna will capture that signal with less noise than a smaller antenna, right? Electrical engineers call this signal-to-noise ratio. The noise is always present, whether it's from background radiation or read noise or whatever. If you increase the system's capability to capture a signal, then that signal overwhelms the noise, and you have a higher signal-to-noise ratio.

An imaging sensor is an antenna. The only difference between an imaging sensor and a radio antenna is that the imaging sensor is designed to capture a two-dimensional set of signals in the nanometer band of the EM spectrum rather than a zero-dimensional signal in the meter band of the EM spectrum. Other than that, they work exactly the same.

What matters isn't the signal per area. If signal per area was the be-all and end-all, small antennas would be fine for all applications. A single radio telescope would be just as effective at imaging distant celestial objects as the entire VLBA spread out over the surface of the planet. But we know that's not true. What matters is the total amount of signal making up an image.

In other words, it will be the same photo except for the depth of field, bigger with a m4/3 lens. For FF users, that's an handicap: for me that's a huge advantage, especially in close-up photography.

Not really. Diffraction is always the same at the same DoF, and FF users can stop down their lenses too. FF users have the option that we don't have of lowering their ISO and getting an even higher signal-to-noise ratio.

MFT lenses do have the capability to stop down relatively farther than FF lenses-- most FF lenses stop down to f/22, where most users are loathe to go; the same DoF is achieved on MFT at f/11. Past that is, for most users, beyond the realm of usefulness because of diffraction softening.

Size of the equipment remains the primary advantage of MFT: Increasing the ISO of a FF camera and stopping down the lens doesn't make it smaller.

If we look at the evolution of m4/3 lens, it goes in two opposite directions: brighter and heavier pro lenses on one side (F/2,8 zooms and F/1,4 primes for examples), and smaller and sharper consumer lens on the other (Lumix 12-32mm zoom, for example).

So let's be back at the original question in this thread: Why not even brighter zooms as the next step in the evolution of our gear?

Probably size and cost concerns. The f/2.0 FT zooms were generally criticized for their being the same size as, and more expensive than, FF f/2.8 glass; enough so that, looking at the systems separately, you'd actually save money and gain capability going for an FF system with a 24-70 and 70-200 over an FT system with a 14-35 and 35-100. While they may have been marvelous pieces of glass, they didn't by any means play to the system's strengths.

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