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Exposure problem


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#1 Eden Lagaly-Faynot

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Posted 14 May 2007 - 04:35 PM

Hello all,

I was reading
the small document Exposure Meters and
The Cinematographer
, by Gerald Hirschfeld, A.S.C, when I came along this excerpt :

On very wide shots such as landscapes, seascapes, beaches,
and snowscapes the incident meter with its hemisphere dome
will give an accurate reading of any subject that would fall
within the boundaries of its calibrated gray scale. Understandably,
a pure white beach or a dead black fire-charred field
would be beyond the norm and compensation would have to be
made for one or the other depending on which was important
to the scene. Stop down one stop for the snow, or open up one
stop for the burnt field, when obtaining your exterior reading
with an incident type meter.



Let's imagine a bright, snowy landscape with a clear blue sky. Following a logical way, I conclude : If the meter show
f:16, then using this stop will cause the snow to be given a grey tendency; so in order to keep the pure and fresh white of the snow, I have to compensate the exposure shown by opening one stop. Before reading Hirschfeld I could bet my house that I was right. But I'm afraid I'm not and worse still I can't figure out where I'm wrong. Maybe a misinterpretation of the document? I think I've missed the point here.

Maybe someone to get me out of this problem?

Thanks for the help,
Eden.
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#2 Brad Grimmett

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Posted 14 May 2007 - 04:54 PM

Opening or closing the iris won't cause a white surface to turn gray. White surfaces reflect more light than darker surfaces. The "correct" exposure on your meter is only exactly correct if the surface you're metering for is 18% gray. Since snow is much lighter than 18% gray it will be overexposed if you expose exactly as your meter says. Closing down a stop will get you close to the correct exposure.
Hopefully that makes sense and I haven't confused you any more than you already were.
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#3 Chris Keth

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Posted 14 May 2007 - 05:07 PM

I would tend to guess that complicating this situation is all of the light reflected off of the snow that then hits your meter dome. I've never shot snow when I wasn't also standing in and surrounded by snow. This would cause your meter reading to include the light that is 1. falling on your subject. This is the light you want to measure with the incident meter. and 2. light reflected off the snow. This light you don't want to measure but really have no choice.

It does seem a bit confusing since it's exactly opposite the usual rule for using a reflected meter in a SLR.
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#4 ryan_bennett

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Posted 14 May 2007 - 05:12 PM

1. falling on your subject. This is the light you want to measure with the incident meter. and 2. light reflected off the snow. This light you don't want to measure but really have no choice.


This is the truth, stop down and it'll be fine.
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#5 Michael Nash

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Posted 14 May 2007 - 05:13 PM

Exposing by the number on your incident meter will cause all subjects to be rendered "correctly," meaning the white snow will be white, the blue sky will be a natural-looking brightness, and a gray subject would be gray.

The article you quoted is saying that sometimes subjects are beyond the range of the film stock, and you might choose to compensate your exposure to ensure you hold detail in extremely bright or dark subjects. In other words, if you want to preserve detail in the snow you might choose to close down your iris a little from what your incident meter tells you.
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#6 Eden Lagaly-Faynot

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Posted 14 May 2007 - 05:25 PM

Well, this is a fast solved problem...
Thanks all for the clear answers :

It does seem a bit confusing since it's exactly opposite the usual rule for using a reflected meter in a SLR.

That was the point I missed when I've recalled articles in instructionals photography book... Sometimes I feel so dumb.

In other words, if you want to preserve detail in the snow you might choose to close down your iris a little from what your incident meter tells you.

I definately get it, thanks again folks for your time and experience.

Eden.
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#7 Chris Keth

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Posted 14 May 2007 - 05:43 PM

Well, this is a fast solved problem...
Thanks all for the clear answers :
That was the point I missed when I've recalled articles in instructionals photography book... Sometimes I feel so dumb.
I definately get it, thanks again folks for your time and experience.

Eden.


No need to feel dumb about that. Every so often everyone gets stuff backwards. I was TA for a guy who shot stuff for about 30 years and I was constantly correcting "stop down" to "open up" and thing like that so the poor students wouldn't get all confused.
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#8 Brad Grimmett

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Posted 15 May 2007 - 05:27 AM

I would tend to guess that complicating this situation is all of the light reflected off of the snow that then hits your meter dome. I've never shot snow when I wasn't also standing in and surrounded by snow. This would cause your meter reading to include the light that is 1. falling on your subject. This is the light you want to measure with the incident meter. and 2. light reflected off the snow. This light you don't want to measure but really have no choice.

Why would you not want to meter the light that is reflecting off the snow? If you're metering at the point where your subject will be, then they (or it) will be getting hit with that same reflected light that your meter is getting hit with. It's not going to hit your meter but somehow not hit your subject.
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#9 Alessandro Machi

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Posted 16 May 2007 - 03:25 AM

Why would you not want to meter the light that is reflecting off the snow? If you're metering at the point where your subject will be, then they (or it) will be getting hit with that same reflected light that your meter is getting hit with. It's not going to hit your meter but somehow not hit your subject.


The light bouncing back might be technically considered backlight since it's bouncing from the opposite direction and therefore not relevant unless one was metering for the backlight.

I'm still not sure about how the term "stop down" was interpreted in the original question by Eden. Stop down would mean if the f-stop reading was originally f-16, then stopping down would mean f-22 and NOT f-11, no?
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#10 Brad Grimmett

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Posted 16 May 2007 - 06:20 PM

The light bouncing back might be technically considered backlight since it's bouncing from the opposite direction and therefore not relevant unless one was metering for the backlight.

He never said the light was coming from behind his subject. If it is then it won't be a problem because it won't be hitting the meter.
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#11 Alessandro Machi

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Posted 17 May 2007 - 12:27 AM

Why would you not want to meter the light that is reflecting off the snow? If you're metering at the point where your subject will be, then they (or it) will be getting hit with that same reflected light that your meter is getting hit with. It's not going to hit your meter but somehow not hit your subject.


Couldn't that be considered backlight since it's coming from the opposite direction than the original sunlight?
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#12 Brad Grimmett

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Posted 17 May 2007 - 03:45 AM

Couldn't that be considered backlight since it's coming from the opposite direction than the original sunlight?

First of all, I don't know how you've decided where this hypothetical light is coming from. The only discussion of backlight started with your post. Second, backlight wouldn't be hitting the meter unless you were metering for that particular direction. Are you familiar with how a meter works?
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#13 Eden Lagaly-Faynot

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Posted 17 May 2007 - 05:34 PM

I'm still not sure about how the term "stop down" was interpreted in the original question by Eden. Stop down would mean if the f-stop reading was originally f-16, then stopping down would mean f-22 and NOT f-11, no?


Hello,

Yes, that was what I mean.

Thanks,
Eden.
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#14 Alessandro Machi

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Posted 17 May 2007 - 05:47 PM

First of all, I don't know how you've decided where this hypothetical light is coming from. The only discussion of backlight started with your post. Second, backlight wouldn't be hitting the meter unless you were metering for that particular direction. Are you familiar with how a meter works?


I assume the light is coming from the sun...

..........The Cinematographer[/b][/i], by Gerald Hirschfeld, A.S.C, when I came along this excerpt :
Let's imagine a bright, snowy landscape with a clear blue sky......


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#15 Evan Winter

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Posted 19 May 2007 - 07:01 PM

Why not take control of the lighting in your scene by using the Ansel Adams approach - break out the spot meter and place your exposure so that all the important elements in your scene fall where you want/need them to fall. Isn't this why most meters sold now are dual meters - reflected/incident?

Why use the wrong tool for the job?

Edited by Evan Winter, 19 May 2007 - 07:03 PM.

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#16 Patrick Neary

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Posted 19 May 2007 - 08:54 PM

Why not take control of the lighting in your scene by using the Ansel Adams approach -


Because in motion pictures you can't vary the processing of each shot to control contrast....
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#17 Adam Frisch FSF

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Posted 20 May 2007 - 04:00 AM

People complicate things so much. Take an incident reading and expose for that. Why would one want to measure the snow - it's supposed to be white, no?
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#18 Brian Drysdale

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Posted 20 May 2007 - 06:54 AM

People complicate things so much. Take an incident reading and expose for that. Why would one want to measure the snow - it's supposed to be white, no?


They seem to.

I've never (to date) had an incorrect reading using an incident meter in the snow, even with 7240. You can point the meter towards the light source (sun) if you want to keep the deep shadows in the landscape or towards the camera if shooting a person or objects (like buildings) that require some shadow.

If you want CU details like the snow crystals you could use a spot meter and the zone system.
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#19 Evan Winter

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Posted 24 May 2007 - 01:37 AM

Because in motion pictures you can't vary the processing of each shot to control contrast....


i'm not talking about processing, i'm talking about exposing. you can use a spot meter reading to place, as appropriately as is possible, the primary elements in your scene on the toe/shoulder of the film. with spot meter readings you know exactly where eveything is that will be exposed and you can manipulate that knowledge to your benefit. with an ambient reading you know, 'if middle gray was where this white dome is now then it would look right'.
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#20 David Mullen ASC

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Posted 24 May 2007 - 01:51 AM

i'm not talking about processing, i'm talking about exposing. you can use a spot meter reading to place, as appropriately as is possible, the primary elements in your scene on the toe/shoulder of the film. with spot meter readings you know exactly where eveything is that will be exposed and you can manipulate that knowledge to your benefit. with an ambient reading you know, 'if middle gray was where this white dome is now then it would look right'.


You can't manipulate it to your benefit -- the point of the Zone System was to spot meter your tonal range and then modify your processing to control the gamma so that the whitest area fell into Zone 10 and the darkest area into Zone 1, so no matter how low-contrast or high-contrast the scene was, you can fit what you wanted to see into the ten zones to create an image with full dynamic range.

Spot metering alone will just give you exposure information, but it doesn't give you the ability to manipulate that range metered unless you relight the scene to alter the dynamic range, because you can't vary gamma through processing as effectively as you can with b&w still processing. Simply over and underexposing the scene to slide the whole range more towards the toe or shoulder isn't really manipulating that range, not in the Ansel Adams Zone System sort of way.
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