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" What Are LV and EV "



 
 
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  #1  
Old May 25th 04, 10:37 PM
Dan Quinn
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Default " What Are LV and EV "

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
  #2  
Old May 26th 04, 02:01 PM
Lassi Hippeläinen
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Default " What Are LV and EV "

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


No. 1/125s and f:16 makes EV15 at any ISO rating.

-- Lassi
  #3  
Old May 26th 04, 03:17 PM
Severi Salminen
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Default " What Are LV and EV "

Dan Quinn wrote:
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


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.

EV does not change as the ISO changes. But it has to _be changed_ if the
user wants to keep the exposure on the negative the same. That is a
different thing.

As Lassi said, EV15 is allways 1/125s at f/16 (or 1/250, f/11 etc.) no
matter what subject, ISO or weekday.
  #4  
Old May 26th 04, 04:10 PM
David J. Littleboy
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Default " What Are LV and EV "


"Severi Salminen" wrote in message
...
Dan Quinn wrote:
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


Correct! (If the light level and resultant film density are held
constantg.)

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.


Hmm. The dictionary at hand defines EV as being LV + film speed, where LV is
the light level.

In the APEX system: EV = AV + TV = BV + SV

Where all values are logs, AV is aperture, TV is shutter speed, BV is the
light level in foot candles.

EV does not change as the ISO changes. But it has to _be changed_ if the
user wants to keep the exposure on the negative the same. That is a
different thing.

As Lassi said, EV15 is allways 1/125s at f/16 (or 1/250, f/11 etc.) no
matter what subject, ISO or weekday.


It seems you're both right. The EV value for a given light level changes
with the ISO, but the shutter speed/f stop combination for a given EV is
always the same.

David J. Littleboy

Tokyo, Japan


  #5  
Old May 26th 04, 08:19 PM
Q.G. de Bakker
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Default " What Are LV and EV "

David J. Littleboy wrote:


It seems you're both right. The EV value for a given light level changes
with the ISO, but the shutter speed/f stop combination for a given EV is
always the same.


No, no, no...

When you start by misinterpeting (!) what EVs are, and begin talking about
the EV value of a light level (Please! You actually DO know better!), then
the "EV value" (i.e. a travesty) changes with the ISO. Yes.

The premisses are completely wrong, so you can not say that the conclusion
is right. Classic schoolbook example of a fallacy: the ex falso quod libet
thingy.

So no, they're not (!!!) both right.




  #6  
Old May 26th 04, 11:09 PM
Dan Quinn
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Default " What Are LV and EV "

Severi Salminen wrote


Dan Quinn wrote:
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


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.


EV does not change as the ISO changes. But it has to _be changed_ if
the user wants to keep the exposure on the negative the same. That is a
different thing.


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.


As Lassi said, EV15 is allways 1/125s at f/16 (or 1/250, f/11 etc.) no
matter what subject, ISO or weekday.


BTW, some of you fellows have'nt by any chance been reading
Phil Davis? Dan
  #7  
Old May 26th 04, 11:40 PM
Dan Quinn
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Default " What Are LV and EV "

"David J. Littleboy" wrote


Hmm. The dictionary at hand defines EV as being LV + film speed, where
LV is the light level.

The EV value for a given light level changes
with the ISO,...

David J. Littleboy


That's the way I learned it and that's the way my meter does it.
Case Closed!

"What Are LV and EV" is a site which can be reached via Google.
I have not actually studied the material at that site. My knowledge
of the subject is from an article in one of three or four publications.
I've not been able to relocate it; it's around somewhere. Dan
  #8  
Old May 27th 04, 10:05 AM
Severi Salminen
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Default " What Are LV and EV "

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


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

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.


Of course, the EV is altered to reflect the correct exposure on negative
- otherwise you would not get correct exposure. Again, EV in itself does
not have to do anything else than speed/aperture combination. When you
indicate certain EV, you don't have to know the ISO, nor does the EV
indicate any ISO. ISO affects EV only because "correct" exposure is
involved. But EV, by definition, does not know about ISO or correct
exposure, or light levels.

From the link you gave - which you didn't even read:

"Each Light Value, or LV, corresponds to a known level of light coming
from a subject.

Each Exposure Value, or EV, represents any of many different but
equivalent combinations of f/stop and shutter speed. For instance, 1/250
at f/8 is EV14, and so is 1/125 at f/11. 1/125 at f/8, one stop more
exposure, is EV13, and 1/250 at f/11, one stop less exposure, is EV15.",
Ken Rockwell

I think this "conversation" is a bit fruitless from now on, so thank
you. Maybe we even remotely agree...

Severi S.
  #9  
Old May 27th 04, 01:02 PM
Pete
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Default " What Are LV and EV "

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. 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.
Pete


  #10  
Old May 27th 04, 01:30 PM
Lassi Hippeläinen
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Default " What Are LV and EV "

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
 




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