Focal length 35mm equivalent, but not F-stop?

Started Jul 24, 2014 | Discussions thread
Great Bustard Forum Pro • Posts: 43,683
Simple solution:

Chikoo wrote:

All camera manufacturer when they publish technical specification of their camera lens publish the focal length and it's equivalent in 35mm. But the same is not done for F-stop. Why?


Pentax MX-1

A 4X optical zoom (28-112mm in 35mm format) at f1.8-2.5 for outstanding depth of field control and beautiful bokeh.

Sony DT 18-135

Focal Length (35mm equivalent) : APS: 27-202.5 mm (35mm Equivalent: 18-135mm)

  • Aperture (Max.) : f/3.5 - 5.6
  • Aperture (Min.) : f/22 - 36

First and foremost, the lens should be stamped with it's *actual* focal length and f-ratio only.  Secondly, if equivalents to another format are given, then the format must be named, and the equivalents spelled out.  Let's use the Pentax MX-1 you gave as an example.

The lens is a 6-24 / 1.8-2.5, should be labeled as such, and it is.  In terms of FF, it is equivalent to a 28-112 / 8.4-11.7.  The way this should be written is:

The Pentax MX-1 has a 6-24 / 1.5-2.5 lens, which is equivalent to a 28-112 / 8.4-11.7 lens on FF, in terms of diagonal angle of view, depth of field, diffraction, and the total amount of light projected on the sensor for a given shutter speed.

Done.  Simple, correct, and no confusion.

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