[Brightcolours]

Ok.  My erorr but you wrote bullshit text. The lens is 24-70f1.8-f2.8. Most site  that talk about 'equivalent' do not adjust the f-stop. As an example:

http://www.dpreview.com/previews/sony-cy...c-rx100-m3

-No were do we see f8 mentioned.T

The 'equivalence' in focal length is used to so people can understand the perspective provided by the lens. Doing the same with the aperture (imho; though I'm 100% sure brightcolour will disagree) is excessively misleading.

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Why do you describe it as an f8 lens when ti is f2.8 ? Anyways I stand by my statement that the graph you provided has no relevance to the conversation as none of the camera are aspc or u4/3. But I will admit my misunderstanding that your calling it an f8 lens when it was really a f2.8 lens. Yes I know brightcolours love to adjust aperture on the lens all the time but I think he is a unique case.

Nothing misleading about it. You just don't understand it, but that does not make it misleading at all.

 

Why does one describe a lens as  70mm when it is 25.7mm? Same thing!

What does the f-number stand for? Focal length divided by the number, gives aperture size.

 

So, the lens is in fact, at the long end, f=25.7mm with max aperture of f/2.8 = ~9.18mm

It is EQUIVALENT to a 70mm lens on 135 film format (commonly referred to in the digital SLR age as "full frame").

Aperture, of course, does not change. It still has a max. aperture of 9.18mm.

Max. f-value then: 70 / 9.18 = f7.63

 

You will have the same angle of the cone of light being captured, you will have the same size of hole letting the light through, you will have the same DOF, everything pretty much similar.

 

It just is that simple. You can also get those numbers by just multiplying by crop factor and not bother with calculating aperture size.

 

Lens equivalence (both focal length and f-stop) is an accepted theory just based on the physics and laws of optics and light, and has been understood by photographers for many decades, especially photographers who dealt with different formats. Of course, in the internet forum age there will always be forum members who don't understand the simple principles and will always try to discredit stuff.

 

Anyway, if one wants to educate oneself on the matter:

http://www.josephjamesphotography.com/equivalence/

http://www.luminous-landscape.com/essays...nses.shtml

http://www.pointsinfocus.com/tools/depth...st=10&u=us

 

Excessively explained.