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In article <>, Neil
Harrington <> wrote:

> > Lenses with the same f/number (more strictly, T/number) will deliver
> > the same number of photons per unit area,
>
> Which is all that matters, so you could stop right there.

for exposure yes, for total light no.

> > It's why small sensor cameras need a higher light level to get the
> > same signal-to-noise ratio or, put another way, why they are noisier
> > at higher ISOs. Their smaller sensor captures fewer photons for a
> > given f/number and light level.
>
> Regardless of format size, *per unit area* the sensor captures the same
> number of photons at the same f-number.

but the area is bigger, so the total is higher.

In article <>, Neil
Harrington <> wrote:

> >> An f/2.8 lens is an f/2.8 lens, regardless of what format it's meant
> >> to cover. Its "light gathering power" is the same as any other lens
> >> of similar f-number as far as photographic purposes are concerned,
> >> disregarding differences in coating, etc.
> >
> > it's light gathering power per unit area is the same (exposure)
>
> Yes. Stop right there.

no

> > but a
> > larger sensor has a larger area so the total amount of light collected
> > is higher.
>
> You didn't stop where I told you.

that's because there's more to say.

> Larger sensor = larger area = more light
> collected = *same exposure*, no difference as long as the f-number is the
> same.

however, more light means better signal/noise ratio.

if you match the noise to obtain the *same* image quality (by raising
the iso) you can use smaller f/stops on the larger sensor. that's where
the difference is.

a good explanation is here:
<http://clarkvision.com/imagedetail/f-ratio_myth/index.html>

> >> Even if you were right about that light-gathering business you'd be
> >> wrong in your conclusion: a half-frame format does not have half the
> >> diagonal of full frame. (It's 30mm vs about 43mm.)
> >
> > 4/3rds is approximately 1/4 the area of full frame,
>
> Yep.
>
> > or two stops,
>
> *Whoa!* where do you get the "or two stops" business?

1/4 the area is 1/4 the light.

one stop is half the light and two stops is 1/4. therefore, a sensor
that has 1/4 the area is a two stop difference.

On 15/06/2011 6:26 AM, nospam wrote:
> In article<isydnbOEtpZxXGrQnZ2dnUVZ_g2dnZ2d@giganews. com>, Neil
> Harrington<> wrote:
>
>>> Lenses with the same f/number (more strictly, T/number) will deliver
>>> the same number of photons per unit area,
>>
>> Which is all that matters, so you could stop right there.
>
> for exposure yes, for total light no.

You really should have stopped with "For exposure, yes."
That is "total light" as far as taking photographs is concerned.

>>> It's why small sensor cameras need a higher light level to get the
>>> same signal-to-noise ratio or, put another way, why they are noisier
>>> at higher ISOs. Their smaller sensor captures fewer photons for a
>>> given f/number and light level.
>>
>> Regardless of format size, *per unit area* the sensor captures the same
>> number of photons at the same f-number.
>
> but the area is bigger, so the total is higher.

So what?
The same f-stop setting gives the same exposure at the same shutter
speed regardless of format size.

You seem to have not grasped the reason why some people use the term
"equivalent f-stop" when taking 4/3, APS and FF.

Using FF as the baseline, all the others have greater Depth of Field
(DoF) with lenses of the same angle of view (IE: 35mm Equivalent Focal
Length [35mm EFL]) with the same f-stop setting.
"equivalent f-stop" is using a aperture (f-stop) setting that gives an
equivalent DoF to 35mm at their 35mm EFL, not the same exposure value at
the same shutter speed.
To get the same DoF on a 4/3 as a FF the f-stop setting must be twice
the size (two f-stops); IE: set the 4/3 to f/1.4 @ 25mm FL (50mm in 35mm
EFL) to get the same Dof as FF set to f/2.8 @ 50mm FL.
For the same DoF on APS as FF the f-stop setting must be 50 percent
bigger (one f-stop); IE: set the APS to f/2.0 @ 35mm FL (50mm in 35mm
EFL) to get the same Dof as FF set to f/2.8 @ 50mm FL.
It gives a much greater exposure setting at the same shutter setting:
the shutter speed must be set higher (shorter time) to compensate for
more light let in by the wider (lower f-stop setting) aperture.

On 15/06/2011 6:02 AM, Neil Harrington wrote:
> David J Taylor wrote:
>> "bob"<> wrote in message
>> news:it5bhf$djb$...
>>> 4/3 camera has a sensor that is about half the length and height of a
>>> full frame sensor (1/4 the area).
>>>
>>> Does that mean a 4/3 camera lense would be half the diameter of an
>>> equivalent full frame lense?
>>
>> .. and half the length, and one eighth of the weight! Doesn't seem
>> to be so in practice, though. You also use the word "equivalent". To be
>> equivalent in light gathering power an f/2.8 full-frame lens
>> would need to be replaced by an f/1.4 half-frame lens. Somewhat more
>> costly to make, if possible at all.
>
> That makes no sense whatever.
>
> An f/2.8 lens is an f/2.8 lens, regardless of what format it's meant to
> cover. Its "light gathering power" is the same as any other lens of similar
> f-number as far as photographic purposes are concerned, disregarding
> differences in coating, etc.

Of course it makes no sense: it is dead wrong.
If "bob" wrote that for the same 35mm equivalent FL that he was after
the same DoF, then two stops wider aperture (for 4/3, in this case) will
get the same DoF as FF (35mm full frame) at the same angle of view lens
(35mm equiv focal length).
It does not work for exposure, only DoF.

> Even if you were right about that light-gathering business you'd be wrong in
> your conclusion: a half-frame format does not have half the diagonal of full
> frame. (It's 30mm vs about 43mm.)

In this case (for 4/3), it is really a quarter-frame format (about 22mm
Vs about 43mm diagonal).
Not that I really believe that the facts will "get in the way" of "bob"s
argument.

In article <4df7e1cf$0$13395$> , dj_nme
<> wrote:

> >>> Lenses with the same f/number (more strictly, T/number) will deliver
> >>> the same number of photons per unit area,
> >>
> >> Which is all that matters, so you could stop right there.
> >
> > for exposure yes, for total light no.
>
> You really should have stopped with "For exposure, yes."
> That is "total light" as far as taking photographs is concerned.

nope. exposure is light per unit area. if you have more area (a larger
sensor), you have more total light distributed over the larger area,
which ends up being the same for a given area.

> >>> It's why small sensor cameras need a higher light level to get the
> >>> same signal-to-noise ratio or, put another way, why they are noisier
> >>> at higher ISOs. Their smaller sensor captures fewer photons for a
> >>> given f/number and light level.
> >>
> >> Regardless of format size, *per unit area* the sensor captures the same
> >> number of photons at the same f-number.
> >
> > but the area is bigger, so the total is higher.
>
> So what?
> The same f-stop setting gives the same exposure at the same shutter
> speed regardless of format size.

but not the same result. the noise and depth of field are different.

> You seem to have not grasped the reason why some people use the term
> "equivalent f-stop" when taking 4/3, APS and FF.

actually you haven't grasped it, since you contradict yourself below.

> Using FF as the baseline, all the others have greater Depth of Field
> (DoF) with lenses of the same angle of view (IE: 35mm Equivalent Focal
> Length [35mm EFL]) with the same f-stop setting.

true, but smaller formats will have more noise (all other things being
equal) so you don't get the same image.

<http://clarkvision.com/imagedetail/dof_myth/index.html>

> "equivalent f-stop" is using a aperture (f-stop) setting that gives an
> equivalent DoF to 35mm at their 35mm EFL, not the same exposure value at
> the same shutter speed.

right, which for 4/3rds, is 2 stops wider.

> To get the same DoF on a 4/3 as a FF the f-stop setting must be twice
> the size (two f-stops); IE: set the 4/3 to f/1.4 @ 25mm FL (50mm in 35mm
> EFL) to get the same Dof as FF set to f/2.8 @ 50mm FL.
> For the same DoF on APS as FF the f-stop setting must be 50 percent
> bigger (one f-stop); IE: set the APS to f/2.0 @ 35mm FL (50mm in 35mm
> EFL) to get the same Dof as FF set to f/2.8 @ 50mm FL.
> It gives a much greater exposure setting at the same shutter setting:
> the shutter speed must be set higher (shorter time) to compensate for
> more light let in by the wider (lower f-stop setting) aperture.

you can also raise the iso, which has the effect of an equivalent s/n
ratio, and then you can use the same shutter speed with the equivalent
f/stop.

that contradicts what you said earlier.

In article <4df7e435$0$13395$> , dj_nme
<> wrote:

> >>> 4/3 camera has a sensor that is about half the length and height of a
> >>> full frame sensor (1/4 the area).
> >>>
> >>> Does that mean a 4/3 camera lense would be half the diameter of an
> >>> equivalent full frame lense?
> >>
> >> .. and half the length, and one eighth of the weight! Doesn't seem
> >> to be so in practice, though. You also use the word "equivalent". To be
> >> equivalent in light gathering power an f/2.8 full-frame lens
> >> would need to be replaced by an f/1.4 half-frame lens. Somewhat more
> >> costly to make, if possible at all.
> >
> > That makes no sense whatever.
> >
> > An f/2.8 lens is an f/2.8 lens, regardless of what format it's meant to
> > cover. Its "light gathering power" is the same as any other lens of similar
> > f-number as far as photographic purposes are concerned, disregarding
> > differences in coating, etc.
>
> Of course it makes no sense: it is dead wrong.

nope

> If "bob" wrote that for the same 35mm equivalent FL that he was after
> the same DoF, then two stops wider aperture (for 4/3, in this case) will
> get the same DoF as FF (35mm full frame) at the same angle of view lens
> (35mm equiv focal length).
> It does not work for exposure, only DoF.

then it's not equivalent, is it?

> > Even if you were right about that light-gathering business you'd be wrong in
> > your conclusion: a half-frame format does not have half the diagonal of full
> > frame. (It's 30mm vs about 43mm.)
>
> In this case (for 4/3), it is really a quarter-frame format (about 22mm
> Vs about 43mm diagonal).
> Not that I really believe that the facts will "get in the way" of "bob"s
> argument.

they do for you though.

On 15/06/2011 8:45 AM, nospam wrote:
> In article<4df7e1cf$0$13395$ m.au>, dj_nme
> <> wrote:
>
>>>>> Lenses with the same f/number (more strictly, T/number) will deliver
>>>>> the same number of photons per unit area,
>>>>
>>>> Which is all that matters, so you could stop right there.
>>>
>>> for exposure yes, for total light no.
>>
>> You really should have stopped with "For exposure, yes."
>> That is "total light" as far as taking photographs is concerned.
>
> nope. exposure is light per unit area. if you have more area (a larger
> sensor), you have more total light distributed over the larger area,
> which ends up being the same for a given area.
>
>>>>> It's why small sensor cameras need a higher light level to get the
>>>>> same signal-to-noise ratio or, put another way, why they are noisier
>>>>> at higher ISOs. Their smaller sensor captures fewer photons for a
>>>>> given f/number and light level.
>>>>
>>>> Regardless of format size, *per unit area* the sensor captures the same
>>>> number of photons at the same f-number.
>>>
>>> but the area is bigger, so the total is higher.
>>
>> So what?
>> The same f-stop setting gives the same exposure at the same shutter
>> speed regardless of format size.
>
> but not the same result. the noise and depth of field are different.

You obviously didn't read what I wrote about "equivalent f-stop".
Are you being deliberately obtuse?

>> You seem to have not grasped the reason why some people use the term
>> "equivalent f-stop" when taking 4/3, APS and FF.
>
> actually you haven't grasped it, since you contradict yourself below.

No, I don't.
It is all about the same Dof and NOT about the same exposure settings.
Read what I wrote, not what you want to see.

>> Using FF as the baseline, all the others have greater Depth of Field
>> (DoF) with lenses of the same angle of view (IE: 35mm Equivalent Focal
>> Length [35mm EFL]) with the same f-stop setting.
>
> true, but smaller formats will have more noise (all other things being
> equal) so you don't get the same image.
>
> <http://clarkvision.com/imagedetail/dof_myth/index.html>

This is relevant, how?

>> "equivalent f-stop" is using a aperture (f-stop) setting that gives an
>> equivalent DoF to 35mm at their 35mm EFL, not the same exposure value at
>> the same shutter speed.
>
> right, which for 4/3rds, is 2 stops wider.

For the same DoF, not exposure value.

>> To get the same DoF on a 4/3 as a FF the f-stop setting must be twice
>> the size (two f-stops); IE: set the 4/3 to f/1.4 @ 25mm FL (50mm in 35mm
>> EFL) to get the same Dof as FF set to f/2.8 @ 50mm FL.
>> For the same DoF on APS as FF the f-stop setting must be 50 percent
>> bigger (one f-stop); IE: set the APS to f/2.0 @ 35mm FL (50mm in 35mm
>> EFL) to get the same Dof as FF set to f/2.8 @ 50mm FL.
>> It gives a much greater exposure setting at the same shutter setting:
>> the shutter speed must be set higher (shorter time) to compensate for
>> more light let in by the wider (lower f-stop setting) aperture.
>
> you can also raise the iso, which has the effect of an equivalent s/n
> ratio, and then you can use the same shutter speed with the equivalent
> f/stop.

No, that would give an over-exposed image.
Wider aperture requires a shorter exposure time or lower ISO setting for
the same exposure value.

Are you sure that you even know which end of a camera to hold?
I am beginning to doubt this, based on what you've written.

> that contradicts what you said earlier.

No, it does not.
I said nothing about raising ISO settings.
you have created that from your own imagination.

On 15/06/2011 8:48 AM, nospam wrote:
> In article<4df7e435$0$13395$ m.au>, dj_nme
> <> wrote:
>
>>>>> 4/3 camera has a sensor that is about half the length and height of a
>>>>> full frame sensor (1/4 the area).
>>>>>
>>>>> Does that mean a 4/3 camera lense would be half the diameter of an
>>>>> equivalent full frame lense?
>>>>
>>>> .. and half the length, and one eighth of the weight! Doesn't seem
>>>> to be so in practice, though. You also use the word "equivalent". To be
>>>> equivalent in light gathering power an f/2.8 full-frame lens
>>>> would need to be replaced by an f/1.4 half-frame lens. Somewhat more
>>>> costly to make, if possible at all.
>>>
>>> That makes no sense whatever.
>>>
>>> An f/2.8 lens is an f/2.8 lens, regardless of what format it's meant to
>>> cover. Its "light gathering power" is the same as any other lens of similar
>>> f-number as far as photographic purposes are concerned, disregarding
>>> differences in coating, etc.
>>
>> Of course it makes no sense: it is dead wrong.
>
> nope

In what version of reality?

>> If "bob" wrote that for the same 35mm equivalent FL that he was after
>> the same DoF, then two stops wider aperture (for 4/3, in this case) will
>> get the same DoF as FF (35mm full frame) at the same angle of view lens
>> (35mm equiv focal length).
>> It does not work for exposure, only DoF.
>
> then it's not equivalent, is it?

Either you want the same DoF (then aperture setting AND shutter speed
must change) or you want the same aperture AND shutter speed setting
(then DoF will change).
You can't have it both ways.

>>> Even if you were right about that light-gathering business you'd be wrong in
>>> your conclusion: a half-frame format does not have half the diagonal of full
>>> frame. (It's 30mm vs about 43mm.)
>>
>> In this case (for 4/3), it is really a quarter-frame format (about 22mm
>> Vs about 43mm diagonal).
>> Not that I really believe that the facts will "get in the way" of "bob"s
>> argument.
>
> they do for you though.

That is a surprise.
The facts demonstrably contradict what you are trying to portray as
"reality".
How does that make me "wrong"?

In article <4df7e87e$0$13391$> , dj_nme
<> wrote:

> >> You seem to have not grasped the reason why some people use the term
> >> "equivalent f-stop" when taking 4/3, APS and FF.
> >
> > actually you haven't grasped it, since you contradict yourself below.
>
> No, I don't.
> It is all about the same Dof and NOT about the same exposure settings.
> Read what I wrote, not what you want to see.

to have the same dof, you need 2 stops wider on 4/3rds, which is what i
said.

> >> Using FF as the baseline, all the others have greater Depth of Field
> >> (DoF) with lenses of the same angle of view (IE: 35mm Equivalent Focal
> >> Length [35mm EFL]) with the same f-stop setting.
> >
> > true, but smaller formats will have more noise (all other things being
> > equal) so you don't get the same image.
> >
> > <http://clarkvision.com/imagedetail/dof_myth/index.html>
>
> This is relevant, how?

it explains it.

> >> "equivalent f-stop" is using a aperture (f-stop) setting that gives an
> >> equivalent DoF to 35mm at their 35mm EFL, not the same exposure value at
> >> the same shutter speed.
> >
> > right, which for 4/3rds, is 2 stops wider.
>
> For the same DoF, not exposure value.

which means to be equivalent, it must be 2 stops wider.

In article <4df7ea5c$0$3035$>, dj_nme
<> wrote:

> >> If "bob" wrote that for the same 35mm equivalent FL that he was after
> >> the same DoF, then two stops wider aperture (for 4/3, in this case) will
> >> get the same DoF as FF (35mm full frame) at the same angle of view lens
> >> (35mm equiv focal length).
> >> It does not work for exposure, only DoF.
> >
> > then it's not equivalent, is it?
>
> Either you want the same DoF (then aperture setting AND shutter speed
> must change) or you want the same aperture AND shutter speed setting
> (then DoF will change).
> You can't have it both ways.

raise the iso on the larger sensor so you can use a smaller f/stop,
which will match noise and dof and keep the exposure the same.