" What Are LV and EV "

"Lassi Hippeläinen" wrote in message
...
Pete wrote:

The EV number itself does not change with exposure settings. If a scene
has
an EV of 12, it has an EV of 12 no matter what.

A scene does not have an EV of anything. EV describes the camera
settings only. A scene may have an LV of 12 on a cloudy day.

However, the ISO rating of
the film affects what combination of aperture and shutter speed you
need.

Yes. From the LV, film speed, and your tastes concerning correct
exposure you can derive an EV. The exposure meter does part of the
estimation by suggesting an EV for the measured LV and given film speed.

You're not changing the EV, you're change the settings that achieve it.

When you change the camera settings, you most likely change the EV,
because the EV depends on aperture and shutter speed. But when done
properly, they can be changed without changing EV. Get a camera with an
EV scale. The aperture and shutter rings rotate in opposite directions,
so that when you turn them in lock, the EV setting remains constant. In
some cameras they are interlocked by default.

If you claim that ISO affects EV, because your exposure meter says so,
I'll show you my camera. Its settings do not change with ISO.

-- Lassi

Look, it's very simple. I've been using manual exposure cameras with EV
numbers for like 30 years. You decide what EV the scene calls for (with or
without a meter), and then you set your combination of aperture and shutter
speed to reflect the EV that you chose to expose for. It's as simple as
that. There's no need to complicate it. Of course the ISO rating of the film
you want to use will affect what shutter speed and aperture combination you
have to use for a given EV.
Pete

Dan Quinn wrote:

You are confusing EV and "correct exposure". EV is simply a
speed/shutter combo (all combinations resulting same exposure) and holds
no info on ISO, subject brightness, correct exposure etc.


It's a wonder people spend money on meters which measure light
intensity in EV.

And it's all so obvious...
Light meters do *not* measure light levels in EV.

They measure light levels and suggest what aperture and shutterspeeds can be
set to get the appropriate exposure for metered light level and set film
speed.

See the four separate entities there? a) light level, b) aperture, c)
shutterspeed, d) film speed?
EV's are no more than a combination of b) and c). Really no more. The other
two entities are just that: two quite separate entities.

They make sense when combined, yes. But that still does not mean that EVs
involve light levels nor ISO values...

My Sekonic measures light intensity at an ISO of 100. That is likely
common practice amoung manufactures. At EV0 the suggested correct
exposure is 1sec at f1. At ISO 50 the EV is 1 and at ISO 200 the
EV is -1. So.

I hope for you that it will measure light intensities "at" other ISO values
too.

Pete wrote:

The EV number itself does not change with exposure settings. If a scene
has
an EV of 12, it has an EV of 12 no matter what.

This is the entire falacy beautifully expressed. A scene does not posses a
property called EV.


However, the ISO rating of
the film affects what combination of aperture and shutter speed you need.
You're not changing the EV, you're change the settings that achieve it.

No, no.
EV only changes when you change the settings, because (and now get this) EV
is nothing but an aperture-shutterspeed combination.
So you can change light levels (the only input the scene has in the entire
exposure metering thing), and you can change the ISO value, but "EV" will
not change one iota.
Until you touch either aperture or shuterspeed setting.

Pete wrote:

Look, it's very simple.

Indeed....

I've been using manual exposure cameras with EV
numbers for like 30 years. You decide what EV the scene calls for (with or
without a meter), and then you set your combination of aperture and
shutter
speed to reflect the EV that you chose to expose for. It's as simple as
that.

No, it isn;t.
It is perplexingly simple, yes. But you're still quite wrong.
You do NOT decide what EV the scene calls for, you decide what EV CORRECT
EXPOSURE calls for.
And correct exposure depends on two things: the light level in the scene and
how much light the film needs.

Then apertures and shutterspeeds come into play (and then EVs too apear):
you need to chose a combination of aperture and shutterspeed that will
govern the amount of light present in the film permited to reach the film.
Set too long a speed or too large an aperture, and the ratio between light
levels both on film and in the scene will be wrong to get correct exposure.
And doing the reverse will have a similar, but inverse, effect on that
ratio.

So given a certain scene light level, and given a certain film speed, there
is only one ratio between the two that will produce correct exposure.
Since both aperture and shutterspeed govern that ratio, it is correct to say
that there is only one aperture-shutterspeed combination that will produce
the correct ratio, the correct exposure.
That combination is the EV that will produce *correct exposure*. The EV that
is appropriate for the scene and film, if you will.
Separate things, you see?

As we all know changing aperture and simultaneously changing shuterspeeds
inversly will keep the ratio between light levels on film and in the scene
constant, will keep correct exposure. And if the combination produces a
certain incorrect exposure, changing both this way will keep the magnitude
of the fault constant.
So (as we all know too) there is not just one aperture-shutterspeed
combination that will produce correct exposure/the correct ratio, but many.
And consequently a certain EV value does not just indicate one such
combination, but all that produce equivalent exposure, all produce the same
ratio (and this is quite independent (!!!) of whether or not this
exposure/ratio will produce the desired/correct exposure for the light level
in the scene and film speed used!). So all are given the same EV value.

That's the entire reason EV values exist: as a simple shorthand notation for
many aperture-shutterspeed combinations.

So understand this, and remember it forever: There are no light levels nor
ISO values in EV, just shutterspeeds and apertures.

There's no need to complicate it. Of course the ISO rating of the film
you want to use will affect what shutter speed and aperture combination
you
have to use for a given EV.

That's not a matter of complicating things. It's a matter of what you (and
others ) are saying just being very incorrect. And that while, as you too
mention, it is all so simple.

Severi Salminen wrote


At least considering the fact that EV has nothing to do with light
intensity...

Are you sure you've not been reading you know who?
My Sekonic measures light intensity in EV units at an ISO of 100.
I suggest leaving LV completely out of your thinking and look only
at EV. Also, the word "correct" appeares very often. I wonder that it
should appeare even once. I wonder it's source.
Perhaps the matter is TOO obvious, TOO simple.

This is one of those forehead slappers when it finally sinks in....
Go find an EV capable meter to help this register in your mind. Set
the EV dial to any number. Now turn the film speed to various
ASA's.... The EV number stays the same, ie, EV 10 = 1/60 at f4.0 at
any ASA. The combination of the metered light and ASA will give the
correct EV number and that in turn will determine the shutter/aperture
combination.

Years ago I used the EV system with my Rollei TLR's and it's a very
nice system once you've used it and much simpler to use than explain.
It's one of those "Throw the cow over the fence some hay" semantic
things.....

On 25 May 2004 14:37:01 -0700, (Dan Quinn) wrote:

From Google enter the above just as written.

Another attempt has been made to dissociate ISO from EV. I'll leave it
up to the reader.

I believe that EV and ISO are inseparable. As those familiar know, the
EV does change as the ISO changes. Ipso facto. Dan

Geez, I feel like I just accidentally walked into the argument clinic in
Monty Python.

Pete

"Q.G. de Bakker" wrote in message
i.nl...
Pete wrote:

Look, it's very simple.

Indeed....

I've been using manual exposure cameras with EV
numbers for like 30 years. You decide what EV the scene calls for (with
or
without a meter), and then you set your combination of aperture and
shutter
speed to reflect the EV that you chose to expose for. It's as simple as
that.

No, it isn;t.
It is perplexingly simple, yes. But you're still quite wrong.
You do NOT decide what EV the scene calls for, you decide what EV CORRECT
EXPOSURE calls for.
And correct exposure depends on two things: the light level in the scene
and
how much light the film needs.

Then apertures and shutterspeeds come into play (and then EVs too apear):
you need to chose a combination of aperture and shutterspeed that will
govern the amount of light present in the film permited to reach the film.
Set too long a speed or too large an aperture, and the ratio between light
levels both on film and in the scene will be wrong to get correct
exposure.
And doing the reverse will have a similar, but inverse, effect on that
ratio.

So given a certain scene light level, and given a certain film speed,
there
is only one ratio between the two that will produce correct exposure.
Since both aperture and shutterspeed govern that ratio, it is correct to
say
that there is only one aperture-shutterspeed combination that will produce
the correct ratio, the correct exposure.
That combination is the EV that will produce *correct exposure*. The EV
that
is appropriate for the scene and film, if you will.
Separate things, you see?

As we all know changing aperture and simultaneously changing shuterspeeds
inversly will keep the ratio between light levels on film and in the scene
constant, will keep correct exposure. And if the combination produces a
certain incorrect exposure, changing both this way will keep the magnitude
of the fault constant.
So (as we all know too) there is not just one aperture-shutterspeed
combination that will produce correct exposure/the correct ratio, but
many.
And consequently a certain EV value does not just indicate one such
combination, but all that produce equivalent exposure, all produce the
same
ratio (and this is quite independent (!!!) of whether or not this
exposure/ratio will produce the desired/correct exposure for the light
level
in the scene and film speed used!). So all are given the same EV value.

That's the entire reason EV values exist: as a simple shorthand notation
for
many aperture-shutterspeed combinations.

So understand this, and remember it forever: There are no light levels nor
ISO values in EV, just shutterspeeds and apertures.

There's no need to complicate it. Of course the ISO rating of the film
you want to use will affect what shutter speed and aperture combination
you
have to use for a given EV.

That's not a matter of complicating things. It's a matter of what you (and
others ) are saying just being very incorrect. And that while, as you too
mention, it is all so simple.

Dan Quinn wrote:
At least considering the fact that EV has nothing to do with light
intensity...

Are you sure you've not been reading you know who?

??

My Sekonic measures light intensity in EV units at an ISO of 100.
I suggest leaving LV completely out of your thinking and look only
at EV. Also, the word "correct" appeares very often. I wonder that it
should appeare even once. I wonder it's source.
Perhaps the matter is TOO obvious, TOO simple.

Here we go again... EV is a unit that describes the ratio of certain
shutter speed and aperture combinations. It is called EV, exposure
value. That has nothing to do with correct exposure, light intensity,
luxes, candelas, foot-candles or any other quantities related to light.

Your light meter does not measure light levels in EVs as EV has nothing
to do with light intensity or subject brightness - as I and Q.G. wrote
earlier. Your light meter measures the light using a silicon photo
diode, then it outputs an EV value using at least the next data: light
measurement from the diode, ISO speed that you have set, K-factor that
is usually factory pre-set (can be calibrated).

The result is an EV value, that you use to take the picture. The EV
value in itself does not have anything to do with luxes, candelas or ISO
settings - only with shutter speeds and aperture. Got it?

Can you answer this question: what is the average intensity (you can
choose the unit) of a subject, that requires me to use EV11 (1/60 at
f/5.6, for example) with my camera?

Yep, you can't answer it...

Severi S.

Here we go again... EV is a unit that describes the ratio of certain
shutter speed and aperture combinations. It is called EV, exposure
value. That has nothing to do with correct exposure, light intensity,
luxes, candelas, foot-candles or any other quantities related to light.

Actually EV can be calculated with either shutter speed and aperture or film
speed and light intensity.
I had some formulas of this a while ago when I was doing a project of
designing a high sensitivity light meter.
But your are right the actual value EV has nothing to do with correct
exposure it's just a ratio.

Jani

Jani wrote:

Actually EV can be calculated with either shutter speed and aperture or
film
speed and light intensity.
I had some formulas of this a while ago when I was doing a project of
designing a high sensitivity light meter.

Be careful, since this kind of thing is exactly why people are so cinfused
about EV.
What you can calculate is "what EV is suitable" given a certain light level
and film speed.

Its like formulas calculating how long a pice of string should be given two
other entities that requie a piece of string of certain length.
While people will never believe that the unit of length is defined by these
other two entities, the somehow do believe that EV is defined by those two
other entities in such calculations.
The reason why they do so is very hard to fathom. But, as we see here too,
they'll jumpt at ny opportunity to demonstrate they do.

So again, be careful. Always explain that what you are calculating is not
what EV is, but what the magnitude in EV of another entity must be to
satisfy the demands set by some goal (in this case correct exposure),
depending on other entities, light level and film speed, as well.

But your are right the actual value EV has nothing to do with correct
exposure it's just a ratio.

And it has nothing to do with either film speed or light levels, yes.