Why do older camera lenses have faster F-stops?

Started Apr 14, 2013 | Discussions thread
EinsteinsGhost Forum Pro • Posts: 11,977
Re: f1.8 equivalents...

Allan Olesen wrote:

EinsteinsGhost wrote:

Allan Olesen wrote:

EinsteinsGhost wrote:

Allan Olesen wrote:

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.

Okay, let us work with facts, as in numbers. Take a baseline for FF.

Are you asking me to do work for you?

I'm asking you to back up your claims with factual information, that demonstrates the few sentences you probably repeat every time on the subject.

I was trying to help by showing you two that your endless "Yes, it will" / "No, it won't" fight could end much faster if you first tried to understand what the other party meant by "exposure".

The need of agreeing on definitions before discussing consequences or results is not a claim. It is just common sense.

Is you the other party? Then, as I asked, illustrate your point on exposure being affected by equivalence, not in sentences but with facts/numbers.

For that matter, if you work with a FF camera that has an APS-C mode, do you expect exposure loss when you select the crop mode? After all, you might have 200/2.8 lens in FF mode, which now functions as 300/4 in crop mode... at the cost of a stop in shutter speed for same exposure?

Or, do light meters require specifying "equivalence" for exposure?

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