exposure of dark evergreen trees?greenspun.com : LUSENET : Large format photography : One Thread
I am amazed how my ambient light meter does a perfect job exposing my Velvia chromes when the light meter is saturated with the same light as the subject is. It seems sensless to make spot meter readings and then interpret the refelctivity % and translate that back into stops to compensate the spot meter reading... however, there is one area that this ambient reading consistently fails me, and I don't know why...
Under broad daylight, evergreen trees are saturated with bright sunlight, my ambient meter is reading the same bright sunlight, so I shoot at the reading on my abient meter.... focused at infinity of course, no issues of bellows compensation... the image is always to dark, by 1 stop to 1.5 stops, so I have to open up an additional 1 - 1.5 stops everytime, and then the evergreens are exposed properly. Does anyone know why this phenomina occurs? Where it really gets me is when the evergreen trees are only a small portion of the scene, then the scene will get exposed properly, but the Evergreens are too dark? Any input would be greatly appreicated. Thank you..
-- Bill Glickman (Bglick@pclv.com), August 27, 1999
I don't know the answer to your question, but I would be interested to know how a spot meter would work in this situation. Is it possible that the shadows between the needles and branches are not being accounted for with the ambient meter?
-- Ben Diss (Ben@Benodee.com), August 27, 1999.
I can think of two things that are happening - meter technique and subject range.
Metering technique: The best way to take an incident reading is probably to point the mater at the camera from the subject. If you point the meter at the light source, the trouble you run into is that the subject receives light at a different angle from how the dome on your meter receives it. By walking into the subject and pointing at the camera, the same light falls on the dome and in the same way as it is falling on the subject. Alternatively, the light you're measuring might be more than what actually falls on the scene. In this case, you're measuring the sunlight falling on the scene. However, the evergreen trees are probably in the shade i.e., in their own shade. So while the sunlight bathes the tops of these trees in the same uniform light your meter is measuring, the part right under the top is in the shade of the tree. That would give you the underexposure of a stop or so. If you can walk into the scene i.e., the trees are not far away, you could walk under them, point the meter at the camera and take the reading which should work appropriately. If you can't walk into the scene, you can try shading the meter and taking a reading or using the meter in your shadow.
Subject contrast range: Alternatively, maybe your contrast range is very extreme. So in order to hold detail in some of the highlights of the scene, the really dark stuff ends up on the toe of the film. The incident light meter really doesn't care about the reflectances of individual areas and it is upto you to see where different areas would fall. Your film can obviously handle only a short range of luminances before it starts throwing stuff away. So dark and VERY dark areas can't really be separated well because they are on the toe of the film or worse, beyond. Now normally, reeally dark stuff makes up small areas in your picture and you can lose that without too much grief. However, if your principal subject area is very dark (or very light), you might want to compensate your meter reading so that instead of this stuff ending up on the toe (or shoulder of the film) where tonal values are compressed or thrown away, you can move them just a little bit (reemember too much pulls them too far in towards middle gray - you don't want to lose the dark value, just separate the dark values out a little better) into the straight line part of the curve where a little more tonal separation can exist between the darks. Alternatively, if your subject contrast range is just so extreme (bright highlights to dark shadows), you can choose to lose detail in one end (let your shadows fade to black - probably the better option with transparency film). If you just have to maintain both ends of the scale you can try other esoteric techniques like rating your film slower and pulling development or preflashing your film.
Hope this ramble helps. DJ
-- N Dhananjay (email@example.com), August 27, 1999.
Wonderful answer. Re-rate your film. But watch your highlights with possibly decreased development as the compensation. The evergreens are in too much shade. Only the tips are exposed to light. Shade your meter and the trees will be exposed properly. Also a yellow #11 or green #58 filter will alter your tonalities in the evergreens. James
-- james (firstname.lastname@example.org), August 27, 1999.
Nope, you're all wrong! It's the chlorophyll. Green foliage can reflect nearly 100 percent of infra-red light, even though it is pretty dark in the visible portion of the light spectrum. Remember all that white foliage you've seen in IR film shots? Unfortunately, the color sensitivity of most meter cells doesn't match the color sensitivity of film. Fred Picker and Dennis Purcell discovered this phenomena when Fred was developing his modified Spot Meter. He corrected his meter with different cells and IR filters. Otherwise, you have to make the adjustment you've described. At least now you know why!
-- Alec Jones (email@example.com), August 27, 1999.
Alec, I'm not sure what you mean - your explanation seems to be contradictory to Bill's observations.
-- Carlos Co (firstname.lastname@example.org), August 27, 1999.
Alec, perhaps you meant that the leaves absorbs ambient light energy? Please clarify.
-- Carlos Co (email@example.com), August 27, 1999.
It seems to me that Dananjay and james are on the right track and that Alec didn't read the question or doesn't know what ambient light metering is. And this is because Velvia simple is a very high contast film. Try Kodak VS100 which abridges more brightness and has by far the most latitude of all slide-films thus far and which is as sharp as Velvia with no irritating magenta-bias. Maybe even the magenta-bias of Velvia coincides with the green of evergreen in such a way that it just does not take that much dark-green.
-- Lot (firstname.lastname@example.org), August 27, 1999.
BTW, at what altitude did you shoot these slides? I mean because of the amount of UV-light, especially in the shadows, which are turned more blue at higher altitiudes, which press away the original greens on slide too.
-- Lot (email@example.com), August 27, 1999.
Thank you all for your input... this just goes to show what an excellent forum this is to bring good ideas and experiences together.
N Dhanajay, you raise some excellent meter technique issues, they were all well explained and I fully agree with them, however I already take them into consideration when metering, so they do not represent the problem here. The contrast range issues does not apply, because sometimes I shoot straight Evergreens with nothing else in the scene and even the trees that are in the front and not the least bit shaded also experience the darkening.
Lot, the altitude is insignificant, I have shot them at sea level and 10,000 ft, and the same result happens. I also check my Gossen 3 color meter beofre every shot, and have not had color temp as a variable yet. However, you raise an excellent point about the bias of Velvia film, and this may an odditity that has no fix, assuming there is other items in the scene you want exposed properly. I will try the Kodak film you suggested.
Alec, you may be on to something here... this is the kind of answer that may make sense, but is not widely known. However, as Carlos pointed out it seems you possibly misworded your answer, becuae remember the shots are darker than expected not brighter. Could you please elaborate on this?
Also, I have a call into Fuji Tech. support, I will advise of any answers they come up with. Thank you.
-- Bill Glickman (Bglick@pclv.com), August 27, 1999.
absence of reflected red, blue, cyan, magenta, & yellow light?
-- Ellis Vener (firstname.lastname@example.org), August 27, 1999.
Hmm, interesting. I wonder if Ellis is onto something. If the trees absorb all the other wavelenghts and in effect reflect just one narrow band of green, that would lead to underexposure. I was wondering if the spectral seensitivity of the meter cell had anything to do with it but I guess not, since a reflected light meter would detect the lower light being reflected by the tree (and anyway, around the green wavelengths, most cells are sensitive). But it does make sense that with an incident meter, you would run into problems since the meter measures all the wavelengths but if the reflected light is being hugely reduced (with the trees absorbing all the other wavelengths), you would get underexposure. I'm a little puzzled by why this happens only with evergreens, though. Would the chlorophyll explanation have something to do there? Ah well, food for thought....
-- N Dhananjay (email@example.com), August 27, 1999.
OK, I spoke to Fuji today... the rep could think of two reasons this would happen. The first is the fact that Velvia is not sensitive to this color green... sprectral sensitvity. He claimed the way to test for this is shoot Kodak chrome... I am trying E100VS, if this exposes the film properly under the same meter reading conditions, then the problem is the film itself. He suspects ths. His other suggestion was that it is possible that evergreen trees actually absorb as much or more light than the color black, and this must be compensated for? He claimed that when black items are exposed in a scene there is rarely detail to be seen, so the lack of detail would go un noticed. There is some logic there for sure.
The strange thing I did not mention was the fact my B&W Polaroids also suffer from the same ill effect... that is how I get the scene right, first nail the Polaroid then adjust for film speed. The Fuji rep said this makes sense because the Polaroid shares most of the same spectral responses as Velvia... that suprised me, but I guess he knows? I will report my findings when I get them..
-- Bill Glickman (Bglick@pclv.com), August 27, 1999.
Bill, I didn't read the "velvia" in the post therefore the confusion. As for Velvia, I shoot it for all my color shots and I never suffer from lack of shadow detail unless the luminance range is too great. I always spot meter so I know what that range will be and expose accordingly. If it is one stop or less I pre-expose the sheet of film to help with contrast. Have you run a film speed test on it to determine if your film speed is correct? An improper film speed will really eat up what little exposure latitude you have with Velvia. But my shots in Yosemite and the Sierra are always colorful from the dark green Ponderosa Pines to the Blue skys to the red sunsets. Beautiful film.If you shoot above 4-6 thousand feet might I recommend an 81B warming filter to help compensate for the blue in the shadows. The blue overwhelms the green wavelengths so a warming filter will bring out the greens better. Art Wolfe and other shooters use this film and you can see what a wonderful film it can be when used right. Hope this helps. James
-- james (firstname.lastname@example.org), August 27, 1999.
It seems odd to me that the B&W Polaroid could be used as a reference for the Velvia exposure in this specific context, because of the known cumbersome sensitivity for greens of any B&W film.
-- Lot (email@example.com), August 28, 1999.
With respect to Alec's answer, I think the point he was trying to make was that light meters tend to be sensitive to infrared light but film is not (unless, of course, the film is infrared film). With a reflected light meter and negative film, this leads to an underexposed negative with a subject that reflects a lot of infrared light such as green foliage. The meter sees the light, takes it into account in giving the exposure information, but the film doesn't see the light. Hence the film tends to be underexposed because the light that the meter took into account in determining the exposure never reached the film. However, I wouldn't think this phenomenon would have any effect when using an incident light meter since with this type meter you're not measuring the light reflected by the subject but rather are measuring the light falling on the subject. Brian
-- Brian Ellis (firstname.lastname@example.org), August 28, 1999.
Yes, Brian. That's what I had in mind. Unfortunately, I was also thinking solely of negative film which wouldn't apply here either. Well, it's a continuation of my motto: "Often wrong, but never in doubt".
If I understand his question now [obviously that is still an issue with me], I would suspect the reason for his underexposure is a difference between the spectral response of his meter and the film. He is saying the foliage is always underexposed, right? Perhaps the film just doesn't give the expected response to that particular color.
-- Alec Jones (email@example.com), August 28, 1999.
When you use the incident meter on really dark subjects, you have to open up a bit. With really light subjects, you have to stop down a bit. Just the opposite of a reflected light meter. Try it on some other subjects of the same relectance & dark tones, then fine tune a bit and you will get it under control. But to change all the other elements of the scene to compensate for dark trees that are a small part may kill the rest of the image through overexposure. Either switch to flatter films such as Astia or EPN, or live with it.
-- Dan Smith (firstname.lastname@example.org), August 28, 1999.
I have to agree with James. When I have used Velvia either 35 or 4x5 I have had to do two things, 1 rate the film at 32 for 35mm and 40 for 4x5. And have used warming filters to warm up the blue. Velvia seems to go too blue in the shadows and I loose information that my eyes do not. An 81 a or b, when I'm shooting early early in the morning an 81c does wonders. My other question is regarding your polaroid shots. Are you filtering for this b+w film as well? A yellow or light green filter will add definition to these green shadows. Good luck on your plight, I am amazed that a Fuji rep would recommend a Kodak product of any type.
-- jacque staskon (email@example.com), August 29, 1999.
From my experience at shooting evergreens, I've always presumed it was the trees absorbing light that resulted in underexposure. If you look at evergreens under afternoon sun, you can't see any detail on the trunks. Any portion of the tree other than the tips of the needles are black or close to it, and velvia's going to make it appear black.
Another note of metering when the tips of the trees are in directly sunlight. I've had a similar problem recently. If you use the direct sunlight ambient reading, the rest of the tree ends up being around 1 stop under. Yet, if you take an ambient reading in the tree's shade, you'll blow out the sky. The only choice is to average. I've gotten good result very late in the afternoon, when the sun is below 30 degrees, as the light rays are close to horizontal, so they can 'penetrate' the tree to expose the trunk to expose parts of the tree that would otherwise be in the shade of needles (depends on the tree, of course).
In the harsh lighting of the SW US, I find this to be especially true (light seems very cold) whereas in humid Asia, it's not as bad (I shoot about 95% velvia). My conclusion was that for the SW, unless the sunlight is faint or you're shooting in the woods, you'll get better results w/ E100S or Astia w/ a warming filter. I'll check some chromes that I recently took on velvia quickloads, as they contain evergreens in the foreground w/ lots of blue sky (taken in the Sierra Nevada at 9000 ft around 5:30pm).
-- James Chow (firstname.lastname@example.org), August 29, 1999.
That is very true of shooting Velvia, or any chrome in bright midday sunlight, be it in Asia or the Southwest US. But the reason is that the film (and especially the color papers for prints) don't have the latitude that B&W or color neg film has. You therefore have to make a choice. Do you want good shadow detail or nice bright highlights? You can have both if you print but not on the slides. If you have good blue skies the information will be on the slide but you have to learn to mask when making a print to pick up the shadows. I just recieved a book by Christopher Burkett and he has the most georgeous color prints I've ever seen. And his images taken in full sun are unbelievable with all the detail you could ask for from subtle deep shadows to brilliant highlights. He shoots 8x10 chromes, mainly Velvia and these have to be seen to be believed. And no computer manipulation at all. All hand printed. Just averaging or bracketing will not ensure good slides as you may lose too much detail at both ends. You can pre-expose the slide material then spot meter to set the correct exposure for the shadows to show density and therefore let the bright areas fall where they may or vice versa. Or you can wait until the light is softer and the subject brightness range comes within your materials bounds. Kodak E100s or Provia/Velvia or any other reversal material will act the same way. With careful positioning you can use a ND grad to help but precision counts. Have fun shooting. James
-- james (email@example.com), August 29, 1999.
I'm interested in the pre-exposure solution to this conundrum (likely the best solution). However, I've misplaced my Adams book explaining the system. To what level and with what neutral subject matter would one pre-expose Velvia for such high contrast situations?
-- John Fowler (firstname.lastname@example.org), September 07, 1999.
It can increase shadow detail by 1/2 stop if done correctly. I used to use a grey card held well out of focus. Now I use a small piece of translucent plexiglass.
-- james (email@example.com), September 09, 1999.
I have found that Kodak E100S pulled one stop produces great results. While I haven't yet tried it with evergreens, I have used it with architectural shots.
My Pentax Spotmeter V was worked over by Zone VI Studios. According to the old web site, they modify the Pentax and Soligor to have IR filters and other good stuff.
Besides pulling the film, try gradient filters like Cokin or Lee, and open up the lens. I remember someone saying that Galen Rowel got a total of a 14-stop range using judicious filter positions. Put the ND part of the filter over the bright part of the scene and go for it. I have one Tiffen split ND filter, and it's convinced me I need something like Cokin or Lee.
-- Brian C. Miller (firstname.lastname@example.org), September 09, 1999.
I must express credit for some of the following theory and paraphrasing, to Roger Hicks & Frances Schultz, the authors of the excellent book "Perfect Exposure." The book has helped refresh the knowledge I learnt from the training I received at the Royal Australian Air Force School of Photography.
Bill, some of the answers to your question have discussed a couple of the least understood factors affecting the procedure of obtaining "perfect exposure." Once the factors are understood you'll need to use logic and an exposure meter. A wise photographer will use both, much like an aircraft pilot trusts an aircraft's instruments, with the knowledge that they've been calibrated and set properly. However, just like an aircraft's altimeter doesn't always read the actual true altitude, an exposure meter doesn't always read the true exposure needed. For the novices out there, opening your mind to such facts is the beginning of your understanding.
So what are those factors I mentioned? The first one is CONTRAST (at the subject, focal plane, and how much is desired during any reproduction of the image). The second one is SPECTRAL RESPONSE (of the exposure meter, and the film). There is also another important parameter that wasn't really explained properly by anyone so far. It's the EXPOSURE METER CALIBRATION to a certain "average" scene reflectance.
I used the term "perfect exposure" because it's impossible to achieve "correct exposure" of everything in a scene. If you create an image that meets your requirements (or the end user's) then it could be said that it's perfect (this applies to composition, sharpness, and all aspects of a photograph).
N Dhananjay correctly discussed Metering Technique and Contrast Range. However, the words "contrast" and "range" in a sensitometric context mean the same thing. CONTRAST describes a range of brightness (or "density" in a film/print image). The "Subject Brightness Range" at the scene is first reduced (very little by good lenses, and sometimes a lot by "flary" lenses) in the camera. You need to take that into consideration if the camera & optics (including filters) cause much flare. Zeiss and Leica lens users will feel smug when they read that! Oh, there is such a thing as a lens that's too contrasty ... when it's "hot" at the image center and a bit dim at the edges. Then you need to understand how much of the "Image Brightness Range" (at the focal plane) your film can record before very dark or very light features will have their brightness range "compressed" on a film's characteristic curve (a graph of density versus log exposure) "toe" or "shoulder." This is when you can't distinguish subtle details in shadow or highlight areas. The textures of the evergreens are an example of shadow detail that can be lost in an image that's too contrasty. At each stage of analyzing contrast, it can be quantified objectively with ratios, logarithms, G- bar's or gammas, density ranges, and paper/scanner log exposure ranges; or subjectively with Zone System values. However, most of the time it isn't necessary to get into that photographer's science of "sensitometry." Basically, a "contrasty" film (like Velvia), or one that is given an amount of development (especially for B&W) that "expands" relatively small ranges of scene brightness so that similar shades from features are more discernible, cannot be expected to record the full range of reflectance from a "contrasty" scene. So those who suggested trying a less contrasty film had a partial solution for you.
The parameter SPECTRAL RESPONSE also needs to be understood. Exposure meters, and each type of film (or image sensor) have a certain fixed response to different wavelengths of ultraviolet, visible, and possibly infrared light. So, they may not (and generally will not) respond to all colors equally. To add to the confusion, usually the response of the exposure meter, film, and our own eyes are all different! But don't worry, perfect exposure is a combination of so many factors that some things cancel others out. A little knowledge and experience can easily compensate accurately enough for the others ... and after all, we still have "latitude." Alec was definitely on to something when he said "you're all wrong!" But as Lot mentioned, Alec was giving an answer to a question that you didn't really ask! That's because you were using an incident reading. I should mention though, what Alec was leading to is that for a reflected reading you need to apply a exposure correction value/factor (how much depends on the meter's spectral response to the metered color) for subjects that are predominantly one color, and then know (from studying a "spectral response graph" if published) how your film (or sensor) will respond to that color too (because a further small exposure correction may be needed). Other issues that Lot and others discussed really don't account for much of the underexposure problem though Bill.
So, if you match the type of film (and/or amount of development, especially for B&W) to appropriate image contrasts, and you've given exposure correction (for meter and film spectral response), but you're still getting underexposed evergreens ... it's probably because of the third and last (thankfully, some of you may be thinking!) misunderstood parameter I have to discuss ...
... It's the EXPOSURE METER CALIBRATION. This may upset some people whose minds aren't open enough to question some of the "rules" that they've learnt about photography: it's a myth that most exposure meters are calibrated to "18% gray" reflectance! 18% gray is a photographic mid-tone half way between black and white. That's true enough, but it's not the magical number that many think it is. Furthermore, many or maybe most scenes don't even reflect that almost legendary value of 18%! The amount of light reflected from so called average scenes may vary from as little as 10% to as high as 25% of the light that is incident upon it (from the sun and sky). More extreme values are common in many parts of the world (even if the solar angle was held constant for all examples). Bill, your subject of the evergreens probably only reflects as little as 3% of the incident light in winter, or as much as 8% in summer. This is logical because evergreens have dark colored (green) leaves, and they, combined with tree branches create many dark shadows. Many exposure meters are actually calibrated to a more modern "average" reflectance of around 12% which is a more representative figure of what's actually "out there." The 18% figure came from the old days when Eastman Kodak's researchers were trying to quantify sensitometric parameters. 18% reflectance may be fairly average for the geographic latitudes (and terrain types) like those around Rochester, New York, but the modern day manufacturers of the Gossens and Sekonics (etc.) we use know a little better now. They should too, because they've had more time to get it "right." So how can you Bill, get it right?
Well, simply put, you need to make correction(s) to what your meter says. But don't go overboard, after all, dark subjects like evergreens should look dark and light subjects should look light. One (often perfect) method is too average reflected and incident readings (duplex metering). The important thing is to get detail where you (or the end user) want's it without sacrificing too much of the rest of the picture's tones. Let's say your exposure meter is calibrated for 12% and you're taking the incident light reading of the sun and sky light falling upon the evergreens. The meter will indicate how much exposure is required to make a subject that reflects 12% of the light, actually look like it's reflecting 12% of the light. Of course that's assuming that the film speed set on the meter, actually works "perfectly" for the film (yes, that's another "rule" that you may have to throw out the window ... film speeds are just a guide, they can be "offset" or vary with lighting conditions or development amount). But the evergreens might only be reflecting 3% of the light, so you have to compensate, keeping in mind that they should still look somewhat dark in the final image. If the meter was calibrated for 3% reflectance, you wouldn't have to do that ... but such a meter wouldn't be good for bright subjects. The point here is that an exposure meter only gives "correct" readings when metering for subjects that reflect about the same percentage of light that the meter is calibrated for. The "phenomena" of needing an additional 1 to 1.5 stops of exposure for the evergreens is mostly because the subject is somewhere between only one quarter (3%/12% = 0.25) to two thirds (8%/12% = 0.67) as bright as what the meter "thinks" will be reflected back from the subject. The remaining difference to the exposure value that you know works is probably made up by the effects of the other factors. Partly CONTRAST (with Velvia, whether by intent or not, your original readings tended towards keeping highlight detail, and that's caused the shadow details to be compressed together on the toe of the "characteristic curve"), and SPECTRAL RESPONSE not being taken into consideration.
By choosing the APPROPRIATE FILM AND/OR AMOUNT OF DEVELOPMENT, to first get the CONTRAST right, and then taking SPECTRAL RESPONSE, and EXPOSURE METER CALIBRATION (or actual subject reflectance) into consideration when taking light readings, you should get perfect exposures almost all of the time! Good luck Bill.
-- Lyndon Gordon (L.Gordon@usa.net), September 08, 2001.