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That a f0.95 lens on 4/3rds = f1.9 (or something) on a FF camera.
This is B.S. The amount of light falling on a given area on the
sensor is the SAME no matter what size a sensor is. It has NOTHING to
do with noise levels and EVERYTHING to do with exposure and aperture.
The lens doesn't magically change its aperture when it is put on a
FF. A 0.95 lens that needs 1/125th sec. exposure on a 4/3rds is going
to need the SAME exposure on a FF at the SAME ISO to achieve the same
illumination level from the sensor. If you don't believe this, take
the SAME lens and shoot with both cameras at the same f-stop and
shutter speed. The images will be the same as far as illumination
levels are concerned, but the FF will have a wider field showing and
will have less image noise.

"RichA" <> wrote in message
news:e841f192-4f36-4517-a839-...
> That a f0.95 lens on 4/3rds = f1.9 (or something) on a FF camera.
> This is B.S. The amount of light falling on a given area on the
> sensor is the SAME no matter what size a sensor is. It has NOTHING to
> do with noise levels and EVERYTHING to do with exposure and aperture.
> The lens doesn't magically change its aperture when it is put on a
> FF. A 0.95 lens that needs 1/125th sec. exposure on a 4/3rds is going
> to need the SAME exposure on a FF at the SAME ISO to achieve the same
> illumination level from the sensor. If you don't believe this, take
> the SAME lens and shoot with both cameras at the same f-stop and
> shutter speed. The images will be the same as far as illumination
> levels are concerned, but the FF will have a wider field showing and
> will have less image noise.

The signal-to-noise ratio of the image is determined by the number of
photons (assuming a low read noise). Taking the f/4 lens on full frame,
then roughly APS_C has half the area, and therefore requires twice the
number of photons per unit area, and the 4/3 has a quarter of the area, so
about four times the photons per unit area. So to capture the same image
with the same SNR, the smaller sensor requires the larger aperture lens.

David

On Thu, 21 Oct 2010 15:25:04 -0700 (PDT), RichA <> wrote:
: That a f0.95 lens on 4/3rds = f1.9 (or something) on a FF camera.
: This is B.S. The amount of light falling on a given area on the
: sensor is the SAME no matter what size a sensor is. It has NOTHING to
: do with noise levels and EVERYTHING to do with exposure and aperture.
: The lens doesn't magically change its aperture when it is put on a
: FF. A 0.95 lens that needs 1/125th sec. exposure on a 4/3rds is going
: to need the SAME exposure on a FF at the SAME ISO to achieve the same
: illumination level from the sensor. If you don't believe this, take
: the SAME lens and shoot with both cameras at the same f-stop and
: shutter speed. The images will be the same as far as illumination
: levels are concerned, but the FF will have a wider field showing and
: will have less image noise.

I guess there's nothing wrong with your argument, but you forgot to stuff the
strawman first. I haven't heard anybody make the claim you're trying to
debunk. It's focal length, not f-stop, that people tend to quote in terms of
its "FF equivalent". I think that's silly too, but it isn't "wrong": a lens of
a given focal length really does produce different results, depending on the
sensor size of the camera on which it's used. Your point, which everyone
accepts AFAIK, seems to be that a given f-stop has the same effect everywhere.
Is there some subtle issue that's sailing over my head here?

Bob

On Oct 23, 5:50*pm, Paul Furman <pa...@-edgehill.net> wrote:
> RichA wrote:
> > That a f0.95 lens on 4/3rds = f1.9 (or something) on a FF camera.
> > This is B.S. *The amount of light falling on a given area on the
> > sensor is the SAME no matter what size a sensor is. *It has NOTHING to
> > do with noise levels and EVERYTHING to do with exposure and aperture.
> > The lens doesn't magically change its aperture when it is put on a
> > FF. *A 0.95 lens that needs 1/125th sec. exposure on a 4/3rds is going
> > to need the SAME exposure on a FF at the SAME ISO to achieve the same
> > illumination level from the sensor. *If you don't believe this, take
> > the SAME lens and shoot with both cameras at the same f-stop and
> > shutter speed. *The images will be the same as far as illumination
> > levels are concerned, but the FF will have a wider field showing and
> > will have less image noise.
>
> M4/3 is half the width, a quarter the area of FX. A quarter the photons,

Photons per pixel is government solely by lens focal ratio. That is
all that dictates exposure.

"Rich" <> wrote in message
news:c1e34f53-a3d8-4a46-ab64-...
[]
> Photons per pixel is government solely by lens focal ratio. That is
> all that dictates exposure.

With a given f/number and focal length, the photons per pixel depends on
the pixel area as well. Larger pixels capture more photons. Bear in mind
that different pixels on different sensors will saturate at a different
number of photons, as the well size is different.

David

On Sat, 23 Oct 2010 18:59:31 -0700 (PDT), Rich <> wrote:
: On Oct 23, 5:50*pm, Paul Furman <pa...@-edgehill.net> wrote:
: > RichA wrote:
: > > That a f0.95 lens on 4/3rds = f1.9 (or something) on a FF camera.
: > > This is B.S. *The amount of light falling on a given area on the
: > > sensor is the SAME no matter what size a sensor is. *It has NOTHING to
: > > do with noise levels and EVERYTHING to do with exposure and aperture.
: > > The lens doesn't magically change its aperture when it is put on a
: > > FF. *A 0.95 lens that needs 1/125th sec. exposure on a 4/3rds is going
: > > to need the SAME exposure on a FF at the SAME ISO to achieve the same
: > > illumination level from the sensor. *If you don't believe this, take
: > > the SAME lens and shoot with both cameras at the same f-stop and
: > > shutter speed. *The images will be the same as far as illumination
: > > levels are concerned, but the FF will have a wider field showing and
: > > will have less image noise.
: >
: > M4/3 is half the width, a quarter the area of FX. A quarter the photons,
:
: Photons per pixel is government solely by lens focal ratio. That is
: all that dictates exposure.

Government by lens focal ratio. I like that. It's a lot better than what we'll
have under the Tea Party.

Bob

On Sat, 23 Oct 2010 14:50:35 -0700, Paul Furman <paul-@-edgehill.net> wrote:
: RichA wrote:
: > That a f0.95 lens on 4/3rds = f1.9 (or something) on a FF camera.
: > This is B.S. The amount of light falling on a given area on the
: > sensor is the SAME no matter what size a sensor is. It has NOTHING to
: > do with noise levels and EVERYTHING to do with exposure and aperture.
: > The lens doesn't magically change its aperture when it is put on a
: > FF. A 0.95 lens that needs 1/125th sec. exposure on a 4/3rds is going
: > to need the SAME exposure on a FF at the SAME ISO to achieve the same
: > illumination level from the sensor. If you don't believe this, take
: > the SAME lens and shoot with both cameras at the same f-stop and
: > shutter speed. The images will be the same as far as illumination
: > levels are concerned, but the FF will have a wider field showing and
: > will have less image noise.
:
: M4/3 is half the width, a quarter the area of FX.

A third, not a quarter. You didn't take into account the difference in aspect
ratios (4/3 for M4/3 vs 3/2 for FX).

Bob