Thread: News flash for beginners on Total Exposure

1. Re: News flash for beginners on Total Exposure

EV = LV at ISO 100.

As I understand the term in simple language, EV is how much light is falling onto something, like film.

By contrast, LV is a measure of the subject’s absolute brightness, or how much light the subject is emitting.

So move your aperture ring (only), or change your shutter speed (only), and EV will change – but LV will not.

However, light bouncing off a black cat will have a different LV than the same light bouncing off an orange cat.

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Hmm. Now that I think about it, one can say that the Pentax Digital & Pentax Spotmeter V (w/ their ISO-100 values) read directly into LV.

2. Re: News flash for beginners on Total Exposure

Originally Posted by rdenney
...
Rick "wondering how many of the younger set don't realize that reciprocity exists except at long exposures, which should correctly be called reciprocity failure" Denney
I did not know that. I suppose if I thought about it I would have figured it out, but it's nice gain knowledge without thinking.

3. Re: News flash for beginners on Total Exposure

Originally Posted by Mike Anderson
I did not know that. I suppose if I thought about it I would have figured it out, but it's nice gain knowledge without thinking.
Well, reciprocity simply means that one unit of light and one unit of time should equal one tenth unit of time and ten units of light, or ten units of time and one tenth unit of light. Low light reciprocity failure is when light levels are so low that the film must absorb light enough to get it off the toe of the response curve before the light falling on the film can begin forming an image. Preflashing film will help here. If light levels are low enough, an image will not form no matter how long you expose it. Short exposure reciprocity failure happens when the duration of exposure is so short that there isn't enough time for the photochemical reaction to take place, getting the film off the toe of the curve. That is, at very short exposures it takes x time to "fill up the toe", only then does the image begin to form. I've never experimented with this less common form of failure, I wonder if preflashing could help here too.

4. Re: News flash for beginners on Total Exposure

E. von Hoegh, great summary, thanks.

5. Re: News flash for beginners on Total Exposure

Heroique, always thought that my Hasselblad had an EV scale, and EV stood for Equivalent Value ,or a combination of f stop and shutter speed that gave the same exposur of another combination of F stop and shutter speed. Thats what I always thought anyways.

Mike

6. Re: News flash for beginners on Total Exposure

Yes, or “Exposure Value,” so very convenient to photographers as an expression of equivalence. ;^)

LV I think is “Luminance Value,” maybe not as important to most photographers, but interesting to distinguish from EV...

7. Re: News flash for beginners on Total Exposure

Thanks that was it ,had a little memory loss ,Exposure Value. Must have been thinking of Stieglitz's serious of Photographs.

Mike

8. Re: News flash for beginners on Total Exposure

Yup ... and after you've figured it all out ... pulled your dark slide ... clicked the shutter and are 45 seconds into your 1 minute exposure ... that little cloud you didn't notice moves over the sun ... that's when you need the SWAG calculation to determine how much more time your shot needs ......... SWAG ... that's an acronym for Swinging Wild Ass Guess ... [a WAG is just a regular old Wild Ass Guess]

9. Re: News flash for beginners on Total Exposure

Originally Posted by Heroique
EV = LV at ISO 100.

As I understand the term in simple language, EV is how much light is falling onto something, like film.

No. EV (Exposue Value) is purely a function of shutter speed and aperture. e.g. EV15 is f16 @ 1/125, or f11 @ 1/250, or any other combination which would give the same exposure. The light is irrelevant and the EV setting remains the same if the camera is in a dark room or pointing at the sun.

Only LV (Light Value) is worked out from the intensity of the light. As you state, EV = LV at ISO 100. This makes it easy to use a lightmeter marked in LV units to set up a camera marked up in EV units - especially at ISO 100 when the numbers coincide. Note that some meters which give an LV reading are actually incorrectly marked as EV.

Originally Posted by rdenney
Not on that Pentax meter, it isn't.
Rick "who doesn't remember seeing 'LV' on the Pentax dial" Denney
See above!

Steve.

10. Re: News flash for beginners on Total Exposure

Originally Posted by Steve Smith
The light is irrelevant and the EV setting remains the same if the camera is in a dark room or pointing at the sun.
Thanks for the clarification, makes sense.

It’s the EV you want to use that would likely change in this situation.

A return to the larger issue: You know the EV you want to use, now it’s on to the shutter speed/aperture combination you want to achieve it. You thought you were ready for the shot? You can’t just simply determine your best exposure and take it – Shame, I say! Shame!!

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