Why do older camera lenses have faster F-stops?

Started Apr 14, 2013 | Discussions thread
Great Bustard
Forum ProPosts: 24,204
Like?
Re: f1.8 equivalents...
In reply to Allan Olesen, Apr 17, 2013

Allan Olesen wrote:

EinsteinsGhost wrote:

Joseph S Wisniewski wrote:

Dave Luttmann wrote:

exposure...no.

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.

One would hope that a term like "exposure" would be well-defined.

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.

Except exposure is defined as the density of light reaching the sensor, where Total Light = Exposure x Sensor Area.

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.

Exactly correct.

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.

Exactly correct.

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.

Exactly correct.  Nicely stated!

Reply   Reply with quote   Complain
Post (hide subjects)Posted by
Keyboard shortcuts:
FForum PPrevious NNext WNext unread UUpvote SSubscribe RReply QQuote BBookmark post MMy threads
Color scheme? Blue / Yellow