How can Sigma make sure the FFF is the best success it can be? Locked

ausJena wrote:

DMillier wrote:

Full frame standard lens: 50mm 4/3 standard lens 25mm

Full frame wide angle: 24mm 4/3 wide angle 12mm

Full frame tele: 100mm 4/3 tele lens 50mm

First thing to note is that 4/3 has never had anything to do with full frame. In no point in the history of 4/3 has any vendor made a full frame format lens to work on a m4/3 body (ignoring adapted lenses). This means that there is no justification at all for calling 4/3 a crop of full frame 135 format. It never has been, it never will be. You also can't use L mount lenses on 4/3 (ignoring adapted lenses) and you can't use 4/3 lenses or m4/3 lenses on L mount. No connection despite Pany's involvement in both, and therefore no justification for calling 4/3 a crop of full frame.

It is true that 4/3 is smaller than 35mm/135/fullframe. But smaller cannot be called a crop unless the same camera bodies and lens systems can use both sensor sizes and they can't.

Sure they can as cropping a larger format to a smaller size makes the result the same as shooting with smaller format. It's not a derogatory term so I'm not sure why make a big deal about it.

Full frame is a format and system in its own right as is 4/3. Neither has anything to do with other and neither is a positive or negative crop of the other. They are entirely independent with their own unique focal lengths and depth of field characteristics. Just keep them separate in your mind and you'll be fine. Insist in translating 4/3 into 35mm terms and you will get in a muddle about something.

A typical example of this would be to start calling a 25mm f/2 4/3 lens a 50mm f/4 lens. You see this all the time on forums and it's wrong. And f/2 lens is an f/2 lens it can never be accurately described as an f/4 lens.

Just like a 25mm lens is always a 25mm lens and can never be accurately described as a 50mm lens

When people attempt this, what they are trying to do is generate a 35mm format equivalence for the depth of field differences between the format sizes. But in doing so they ignore the primary reason for calling a lens f/2, which is the amount of light it lets in.

It is not just a matter of DoF. A f/2 on different formats capture different amount of light. The amount of light captured and DoF go hand in hand - no free lunches.

And no one doing the equivalence dance ever bothers to do it properly and say something like:

"A 4/3 25mm f/2 lens, has the same angle of view as a 50mm f/2 lens on full frame, the same bright f/2 aperture, but the depth of field it has is similar to that exhibited by a 50mm f/4 lens on full frame.

Aperture diameters: 50mm/2=25mm, 25mm/2=12.5mm. 25mm diagonal is twice as much as 12.5mm, the area four times as much. As the field of view is the same (50mm on FF, 25mm on m/43), the scene luminance is the same for both systems, but the larger aperture of FF lens means the FF captures 4 times more light from the scene.

So calling is "same bright f/2 aperture" is not only misleading, but also false (as the f, i.e. focal lenght in this formula is different on each systems, thus 25mm and 12.5mm apertures). One might call it "same bright f-number" - it would be true, but still misleading.

If we do double blind test, then in principle a camera with a sensor quarter the size at 25/2 will produce output that is equal to that of 50/4 on a larger sensor. It captures the same light.

If a 4/3 sensor has the same pixel count as a full frame sensor, it will have a reduced signal to noise ratio, and noise will be more visible (assuming same generation sensor tech)".

Actually it is not that simple. If we require a certain DoF and can not take advantage of the larger format's larger saturation signal (e.g. shooting small exposures like low light action at certain desired DoF), then all the formats perform identically in the context of SNR.

Nobody ever bothers to properly spell out all the meaning of equivalence, they just stumble along with some half-assed jumbled up mess.

Just learn the characteristics of the formats you use and stop converting everything into full frame terms. It's an archaic practice.

It's awfully practical if one wants to compare systems of different formats, different formats themselves, or for example figure out how a certain picture could be replicated on another format.

Since different formats perform differently with the same f-number (and focal length too naturally), there is a need for a clear and simple way to see how the systems compare when doing the same or similar job. Crop-factor is simply practical. The fact that FF sensor size is being used as the unit is just how it is. It doesn't make it any better or worse.

I agree. Using 35mm as the "full-frame" standard, and calling smaller sensors crop sensors, seems to make a lot of sense to me.