Why do older camera lenses have faster F-stops?

Started Apr 14, 2013 | Discussions thread
Allan Olesen Veteran Member • Posts: 3,391
Re: f1.8 equivalents...

EinsteinsGhost wrote:

Joseph S Wisniewski wrote:

Dave Luttmann wrote:


Exposure... yes.

Come on Dave, you've shot many different film formats and different digital formats. Do you shoot the same ISO in all formats?

No, it doesn't. The f-stop equivalence applies to DOF, not to exposure.

It depends on your definition of exposure.

If exposure means "total amount of light reaching the sensor" then exposure will be different at same f-stop, same shutter speed and different sensor size.

If exposure means "amount of light per unit of sensor area" then exposure will be the same at same f-stop, same shutter speed and different sensor size.

As far as I know, the last definition is correct - which actually makes exposure irrelevant as a comparison parameter when comparing cameras with different sensor size.

What matters in such a comparison is the total amount of light reaching the sensor, and you WILL have to calculate the equivalent f-stop if you want to know that.

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