Why do older camera lenses have faster F-stops?

Started Apr 14, 2013 | Discussions thread
Joseph S Wisniewski Forum Pro • Posts: 34,136
Re: f1.8 equivalents, yes, equivalents!

Dave Luttmann wrote:

Dave Luttmann wrote:

EinsteinsGhost wrote:

Barrie Davis wrote:

EinsteinsGhost wrote:

Joseph S Wisniewski wrote:

Dave Luttmann wrote:

Joseph S Wisniewski wrote:

EinsteinsGhost wrote:

Joseph S Wisniewski wrote:

Yes, because it's micro four thirds, and the DOF and you need f0.9 to have the light gathering and DOF equivalent of the "plastic fantastic" $100 f1.8 lenses on FF. So, some old "cine" lenses get reincarnated.

DOF yes (at same FOV), exposure no.

Exposure yes.

Cut the sensor area into a quarter of what it was, and you have 1/4 of the photons in the picture, so you need to throw 4x the light at it to get the same results. Just like in the film days, when tri-x was probably my most shot film on the 4x5, while tech pan was one of my favorites on 35mm.

Physics is a bear.

Exposure...no.  I get the same shutter and aperture rating using a FF camera at iso 100 and f8 as I do on an m43 body.


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.

Ahh... That is what you think, is it?  I'll bear your opinion in mind for the future.

"Observation" should trump "belief". Try it.

I did.  I set up my Fuji x10 at iso 100, f 5.6, 50mm equiv FOV and obtained the exact same shutter speed on my Nikon D700 with the same settings.  Pretty easy test....

Which simply proves Joseph and Barrie are mistaken.

Do the two pictures look anything at all similar?

What's that word at the top of the last few posts, "equivalents", actually mean? You described two setups that take two very different looking pictures. FOV is equivalent, that is all. Not DOF, not dynamic range, not noise.

50mm ISO 150 f2.8 1/200 sec on FF takes essentially the same picture as 75mm ISO 100 f4.2 on APS-C.

Look at today's news from Sigma

"Sigma has announced the 18-35mm F1.8 DC HSM Art lens for APS-C DSLRs - the world's first constant F1.8 zoom. The lens covers a 27-52.5mm equivalent range, and will be available in Canon, Nikon and Sigma mounts. As yet there is no announcement of a recommended price. The lens will offer the light-gathering and depth-of-field equivalent of a constant F2.7 on full-frame, which may under-cut the need for some photographers to change formats." (emphasis mine)

The camera companies understand the equivalence. The dpReview staff understand it, too.

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Rahon Klavanian 1912-2008.
Armenian genocide survivor, amazing cook, scrabble master, and loving grandmother. You will be missed.
Ciao! Joseph

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