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Author Topic: Light Metering  (Read 8874 times)
Jonathan Wienke
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« Reply #40 on: February 07, 2005, 09:10:33 AM »
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Thank you.
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howard smith
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« Reply #41 on: February 16, 2005, 05:47:07 AM »
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Sorry for any apparent contrdiction.  My thought is that if the image isn't properly exposed, some correction can be made during processing and printing.  The greater the dynamic range of the original, the less the effect of improper exposure (more latitude).  But latitude doesn't always make an effective substitute for correct exposure of the original.
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Jonathan Wienke
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« Reply #42 on: February 17, 2005, 03:11:56 PM »
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Similar to reducing the developing time with b&w film? Shadows relatively unaffected but the highlights are depressed. Before I learned to use the Zone System, the vogue was to overexpose (increase shadow detail) and underdevelop (lower highlights). Flatten the film's curve.
That's the general idea, devise a way to gradually decrease the photodetector's sensitivity to light as the charge level increases, so that the electron well will never quite fill completely (at least from light exposure, dark current would be another issue entirely), and response curve between light exposure and output voltage going to the ADC will more closely match that of the human eye. That will increase dynamic range that can be built into a photodetector well of any given size.
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howard smith
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« Reply #43 on: February 20, 2005, 12:06:51 PM »
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"I can't help wondering if b&w film in Ansel Adams' days had had a textural range of 10 stops, would Adams have devised the Zone system?"  In a word, certainly.  He would still have wanted to match the film to the paper.
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Ray
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« Reply #44 on: February 21, 2005, 12:54:46 AM »
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Eric,
I understand fairly well what you've just written and I'm not criticising the zone system as devised and used by Ansel Adams, I'm merely arguing a point I made much earlier in the thread that all these considerations that resulted in the zone system, and also today results in practices such as 'expose to the right', are fundamentally based in the inadequacies of the medium (film or sensor) to capture the full dynamic range of a scene, with full texture, as the eye sees it.

We all know (or should know) that the camera does lie. And one respect in which it lies is its portrayal of dense shadows as black, and/or whitish surfaces such as a white shirt or white paint on a house, or clouds in the sky, or parts of a sunlit waterfall, as white as the paper it's printed on.

The eye simply doesn't see it this way. At least my eye doesn't. I'd prefer to have a flat image containing full detail in all parts of the image and then choose which parts I'd like lighten and darken according to taste and even change my mind about it 2 years later or even 10 years later.

The only way I can do this at present is to take multiple exposures on a tripod and hope the wind doesn't interfere.
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howardbatt
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« Reply #45 on: February 23, 2005, 09:07:24 AM »
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What a great outlook, Ray. That's what got me wondering in the first place about metering. It seems the tech impulse can take over and photography becomes mechanical with the result measured by "accurately" representing what was "actually" there. Who knows what was "actually" there when Ansel Adams clicked the shutter? Who cares? What's important is what happens when we look at the result. That's the nature of the art. The tech side is the reason so many people refuse to acknowledge the artist behind the lens - anybody can "take a picture."

There were good images made with a pinhole camera and a guess at exposure. And there are good images made with Ebony view cameras. But the impact of the picture on the viewer depends on the skill and artistic emotion of the person who composes, captures and creates the result. I suggest many people - including many in this forum - have created images every bit as "good" and better than Adams. But so many treat "understanding" the Zone system as some kind of holy grail. Learning how to stroke with a brush and which kind of canvas to use does not a great master make. Using the tools available to record and emotion in a way it's understandable to viewers is the trick - I think.

God - how I lust after the Canon 1ds Mark II and the hugely expensive medium format digital backs.  But I have spent the limit on my EOS 20D and will be an article in the news if I even THINK about spending $8,000 on a camera.  So - I watch and read in this forum and enjoy learning how to use what I have available to me (which is considerably more than Ansel Adams ever imagined) to make pictures people enjoy.
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Ray
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« Reply #46 on: February 23, 2005, 10:04:49 PM »
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I should add that I'm no expert on Ansel Adams. This particular shot, Moonrise over Hernandez, sticks in my mind because Howard mentioned it during a long thread on the correct exposure for the Moon, over a year ago.

I think it's a great example of the circumstances of a shot contibuting to its fame. We all like a story or narrative. Whatever this shot lacks, it's made up for by (3 prepositions together; is that grammatically correct?) the narrative surrounding the circumstances of the shot.

I've only seen small jpegs of this photo but I'd like to see a full enlargement showing the full tonal range. As an aside, it's interesting to note that there appears to be a rule of thirds in operation here  Cheesy . The foreground with graveyard and church, the lower third; the bright bank of clouds and the moon above, the middle third, and the black sky above the moon, the upper third.

Could be a bit symbolic  Huh .
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Ray
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« Reply #47 on: February 24, 2005, 07:49:11 PM »
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Howard,
Where have I written that the goal of all photographic production should be to accurately portray the scene as it was? We all know that doesn't necessarily apply to art photos. I have no doubt that the black sky above the moon at Hernandez was not really black when Ansel released the shutter.

Nevertheless, I would like my camera to be able to accurately record the scene in front of me within its two dimensional limit as much as possible because it increases my options. I'm not into 3 dimensional stero photography yet  Smiley .
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howard smith
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« Reply #48 on: February 25, 2005, 09:21:29 AM »
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"I much prefer sitting in front of a computer, ... ."  I hear that can be unhealthy, too.  I guess no one will ever accuse you of being wet behind the ears.  "[T]rying to be brief" seems, at least to me, to pretty well describe your approach to making images as well as defining photography.  As someone has already said, to each his own.  Enjoy your trip to Italy.
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howardbatt
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« Reply #49 on: February 04, 2005, 01:41:08 PM »
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Thanks to all very much.  

I'd read an article by a pro who advised putting the camera on "manual" and forgetting about the reflective metering if "really good" results were desired.  Then I started reading more - there's many articles about why an incident meter should be part of one's kit.  So - I looked at the Sekonic L358 and it sounded like a magic box.  Then I thought that, basically, all I want to do is measure light and I shouldn't have to spend big bucks to do that.  Plus, in this digital age, I can merrily shoot 100 test shots without worrying about film.  On the other hand, I figured B&H wouldn't be carrying them if nobody was buying.  So the toy bug in me got reinforced.

When I read your replies and remembered that Ansel Adams probably didn't use a $300 - $600 digital light meter - I felt a lot better.

Thanks
Howard Batt
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howardbatt
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« Reply #50 on: February 06, 2005, 10:03:01 AM »
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Dinarius, that's exactly what caused me to ask the question - if I'm looking at a landscape from a mile away, why would I use an incident meter?  Then I read the Sekonic site (there's an interesting two page article there) and some others who make the basic argument that the light "falling on the subject" is different from the light "reflected from the subject" because of color and tone.  In camera reflected light meters try to see everything as 18% grey and, therefore, the result will be biased to grey - even a white or black plate.  There's a picture of a white fox in the snow - an "impossibility" apparently with a reflected light meter.  But - to use the incident meter for landscape photography, I *would* have to walk the five miles to the landscape to measure the shadows with the incident meter - because the light falling in the shadow areas isn't the light falling outside.  The color and tone are different and could only be measured at the location.  That - if I understand it correctly - is why Sekonic recommends the spot meter for such situations.  Take several spot meter readings and average them - precisely what my camera does automatically or manually.  If all I had to do was meter the sunlight incidentally - then I could use the small (letter sized) neutral grey card I have in my backpack.  Stick it in the sun, meter it and be done.

Or am I missing something?
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howardbatt
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« Reply #51 on: February 11, 2005, 08:58:08 AM »
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I think I've figured it out and I've decided a good handheld incident light meter is just as important in the digital world as it was with photography before the in-camera meter.

The key that I've gleaned from reading a lot about it in the past couple of weeks is this:  if I can control the light - as opposed to simply measuring it - then I need an incident light meter.  So - landscape photography:  if it's big like an island in the sun with palm trees and lots of water, the in-camera meter will do everything because I can't alter the light in any way.  But, if I'm photographing a flower in the shade or a group in a room and want to adjust the light between shadows and highlights or "warm" the scene, then simply bracketing and picking the "best" result won't work - the meter will simply read what it sees and the picture will be exposed accordingly.  To adjust the ratio of fill and back and main light and to use shadows for a desired result demands a good meter to place the lights and determine their power or a lot of experience with them to achieve a particular result.  To "paint with light" where the light can be controlled requires the meter as the tool that helps the photographer properly place the paint.

A fascinating forum this is - knowledgeable people to put me on the track and create the desire to learn. Thanks
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Ray
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« Reply #52 on: February 16, 2005, 01:22:32 AM »
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I thought the problem was likely solvable, and it appears it is in Photoshop.............

The point was that increasing the dynamic range of a digital camera to 12 stops would not represent an alternative to correct exposure any more than 12 stops of B&W eleminates exposure problems. It provides more latitude to get acceptable results, but not a fix. Variable contrast printing paers can cover up some exposure/developing problem, but not fix them.

To get the results you expect, there seems to be little alternative to correct exposure
Howard,
You seem to be contradicting yourself here. You agree that the problem is solvable with PS and then go on to say that it's not really solvable.

Variable contrast printing is not so relevant in the digital world since the source can be adjusted to suit any type of paper.

However, there could still be an 'expose to the right' issue even with a camera with a 12 stop DR. Perhaps this is what you are referring to.

If we take the example of the indoor scene with a view out the window; an evaluative, automatic exposure with current DSLRs would severely overexpose the view through the window, blowing lots of highlights, particularly in the sky, and would produce a perhaps more reasonable but still underexposed interior.

Neither part of the image is going to be correctly exposed. You might be able to recover a significant amount of detail in the clouds (if there were any), but the blue channel will be severely clipped and the sky, if it was blue, will range from grey to sickly cyan.

The interior will exhibit lots of noise due to underexposure. If too objectionable then Neat Image will help, but the result will still be slightly degraded. In fact, the image over all, after extensive processing, will be somewhat degraded.

Supposing the camera were capable of 12 stops DR. The interior part of the image would then look as though it had been shot with a current 6 stop DR camera exposed to the right, and the same for the view through the window. Essentially, one would have two images, the interior and the window, both of which would look as though they were two separate but correct exposures taken with your current average DSLR.

You could argue (and I wonder if this is your point), if the view through the window was irrelevant to the composition, then one might choose to expose the interior fully to the right of the 12 stop range in order to get more levels. However, I doubt there would be much advantage in this. I suspect any future 12 stop DR camera will only achieve such a spectacular DR by compressing the brighter values; ie. it would not be a linear imaging device like current cameras.
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howard smith
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« Reply #53 on: February 17, 2005, 03:47:56 PM »
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OK. Overexpose would move the histogram to the right. Can the response be flatten? I think so long as the highlights aren't overly clipped or blown out.

I can see how a larger dynamic range could be helpful.  It would allow more "overexposure?"
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Ray
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« Reply #54 on: February 20, 2005, 12:20:36 PM »
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In a word, certainly. He would still have wanted to match the film to the paper.
Yes, but I fail to see how a zone system would help to match the film to paper. 10 stops of full texture would result in no pure blacks or whites on the negative at all, except in very rare and exceptionally high contrast scenes. The matching would all have to take place through choice of developer and development time, choice of paper grade and such techniques as dodging and burning .. would it not?
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Eric Myrvaagnes
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« Reply #55 on: February 20, 2005, 11:03:41 PM »
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I think you are misunderstanding the Zone system. With film photography there are three different exposure ranges you need to be concerned with.

  First is the total range of luminances in the scene you are photographing.

  Second is the range that the film can accomodate.

  Third is the range of tones from black to white that the printing paper can produce.

If Range 1 (scene) is fewer stops ("Zones") than Range 2 (film), you have some leeway, and the preferred exposure is generally to "expose to the left" so as to minimize grain. But if Range 1 is greater than Range 2, you must give up some of one or both ends of the scene's brightness range. It's up to you to choose. In any case, you use exposure, development, paper grades, and sometimes other more arcane techniques to translate scene brightnesses into print tones.

The Zone System simply provides three different (but related) useful schemes for measuring the scene and knowing what to do to the film and paper so as to make the print reflect what you felt was important in the scene. And the key to using these effectively is previsualization -- being able to look at a scene and have a pretty good idea what is possible to get in the print, even before you click the shutter.

With digital, you still have the same three ranges to deal with (the second is what your sensor can hold), but Range 2 may be longer or shorter than the range of any given film. And with digital you have more tricks you can play with (levels and curves, for example). But still, if you know the limits of each stage of your medium, you can maximize the possibilities. So the Zone System applies just the same as with film. But you have more ways to play with the translation from scene to print.

I hope this helps a little.

Eric
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-Eric Myrvaagnes

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howardbatt
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« Reply #56 on: February 23, 2005, 09:09:28 AM »
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ooops - the "outlook" I admired was Howard Smiths.  I was listening to the radio and "Georgia on my mind" made Ray come to mind and .....
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Ray
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« Reply #57 on: February 23, 2005, 08:49:20 PM »
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It seems the tech impulse can take over and photography becomes mechanical with the result measured by "accurately" representing what was "actually" there.  Who knows what was "actually" there when Ansel Adams clicked the shutter?  Who cares?

Sounds to me you should take up painting. The camera is a mechanical device and is designed to be as accurate as possible in its role of capturing (or representing) what was actually there. What you do with that 'accurate' representation is up to you. It's easy to turn a photo into the appearance of a painting, but very difficult to do the reverse. It's easy to make a sharp photo look blurred, but difficult to do the reverse. It's easy to create black shadows where none exist, but difficult to create detail from those black shadows.

Lots of people actually care about what the scene was like when Ansel Adams pressed the shutter at Hernandez. The place has become almost a Mecca for admirers of this photo. People rue the fact that the shot is now unrepeatable because the foreground has changed so much over the years. Because Adams was rather lax at recording the dates of his images, astronomers have even taken the trouble to precisely determine the date of this image for posterity - 4.05pm on October 31, 1941.

I'm not sure what you are on about in this post.
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wolfnowl
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« Reply #58 on: February 24, 2005, 07:37:33 PM »
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Gee - it's nice to see a dinosaur here. My first "real" camera was an Argus C-3.  I left the Hawkeye crowd in the dust with that and a $9.00 light meter.
Another dinosaur... my first 'real' camera was my dad's Argus C5.  I still have it somewhere in a box...

Mike.
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Ray
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« Reply #59 on: February 25, 2005, 07:34:30 PM »
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"[T]rying to be brief" seems, at least to me, to pretty well describe your approach to making images as well as defining photography.
This is a completely wrong impression you've got, Howard.
On some photos (just a few) I've already spent the equivalent of several weeks 8 hours a day on each one, and they are still not to my satisfaction. I've made several trips to the same location to reshoot but never has everything been just right. The weather is either too hazy or too windy or I make mistakes. They are stitching projects.

There are other (single) images that I keep reworking as my knowledge of photography increases and as the equipment and programs become more sophisticated.
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