OK ALL YOU full frame camera fanatics

Started Nov 14, 2012 | Discussions thread
Great Bustard Forum Pro • Posts: 40,342
Did someone say "nonsense"?

JoopN wrote:

This is totally nonsense, a lens is f/2.0 or not, on other systems its also f/2.0.

But what does f/2 mean in terms of the visual properties of the final photo?  No more or less than saying the lens is 50mm.

The fact of the matter is that 50mm f/2 on 4/3 is equivalent to 100mm f/4 on FF:

  • 50mm f/2 on 4/3 (mFT) is equivalent to 100mm f/4 on FF.
  • By "equivalent to", I mean that it results in the same AOV (diagonal angle-of-view) and aperture (entrance pupil) diameter:  50mm / 2 = 100mm / 4 = 25mm.
  • The same perspective (subject-camera distance), AOV, aperture diameter, and display size results in the same DOF (and diffraction softening).
  • The same aperture diameter and shutter speed (usually attained by upping the ISO two stops on FF) results in the same motion blur as well as total light falling on the sensor.
  • The same total light falling on the sensor results in the same noise if the sensors are equally efficient (less noise if the sensor is more efficient, more noise if the sensor is less efficient).
  • Other elements of IQ, such as resolution, bokeh, flare resistance, etc., as well as elements of operation, such as AF speed/accuracy, size, weight, etc., are not covered in this use of the term "equivalent".

After all, as photographers, aren't we interested in what the photo looks like, as opposed to the camera settings that get that photo?

Now, "equivalent to" does not mean "equal to".  Indeed, a 50 / 2 macro on an E1 at 50mm f/2 will produce a different photo than a 35-100 / 2 at 50mm f/2 on an E5.  But we still say "50mm f/2" for both scenarios, as they are equivalent.

Likewise, 50mm f/2 on 4/3 is not equal to 100mm f/4 on FF, but it is equivalent.

The FF fanatics just trying to say that their systems are better because more light is falling on the pixel.

Not the pixel, but more light (two stops more) falls on the sensor for a given exposure.

If this is true, why is the cap between FF, APC and 4/3 so small?


At a certain point in a FF lens the ray of light is spread out over a bigger surface while the ray of light almost goes unchanged to a 4/3 sensor.

Neither here nor there.  It doesn't matter how spread out the light is, just the total amount of light collected.

This is why you can say that FF has to double the focus length in order to get the same image circle, but that does not mean that you have to double everything.

Again, neither the focal length nor the f-ratio are meaninful measures when comparing between formats.  What are meaningful measures are the AOV (angle-of-view), the aperture (entrance pupil) diameter, and the shutter speed.

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