# What is equivalence good for?

Started Jul 25, 2014 | Discussions thread
Re: What is equivalence good for?

Just another Canon shooter wrote:

mostlyboringphotog wrote:

Just another Canon shooter wrote:

mostlyboringphotog wrote:

Just another Canon shooter wrote:

olliess wrote:

Just another Canon shooter wrote:

olliess wrote:

Just another Canon shooter wrote:

...the answer is as simple as that: just multiply three numbers (F-stop, FL and ISO) by the crop factor.

I think multiplying the ISO by the crop factor would actually be equivalent to a "screwup," but I don't want to derail this fascinating and original conversation. So please carry on.

It would be a screwup if you don't. GB does not want to include it because he does not want to be criticized on the basis that different sensors have different noise characteristics. Recent sensors have remarkably close QE, so this is not a more important problem than, saying that different lenses with the same f-stop differ by their t-stops.

Umm… the difference between f/2.8 and 2x f/2.8 = f/5.6 is 2 stops. The difference between ISO 100 and 2x ISO 100 = ISO 200 is only 1 stop.

Oops, multiply by the square of the crop factor, my bad.

crop factor for f-stops but square of the crop factor for shutter speed (the other direction) or ISO; and why is that?

Total light: it is the light over the whole sensor. With the same intensity, you get the crop factor squared times the light with the bigger sensor.

To put it differently, FL and f-stop are linear quantities, total light is quadratic, and the ISO compensating for that is of the same type.

The answer I as looking for was because f-stop is already the equivalent linearization of the aperture area.

I would not use the term linearization since I am used to its math meaning.

Likewise, I would not use "equivalent aperture" for sensor size as I'm used to its "equivalent exposure" meaning.

mostlyboringphotog's gear list:mostlyboringphotog's gear list
Panasonic Lumix DMC-GM1 Pentax 645Z Nikon 1 J5
Complain
Post ()
Keyboard shortcuts: