Different measurements with spot vs incident metering on same target?

[tomfrh]

Does incident work better for slide film? I've always used reflected for
Slides.

 

[Sirius Glass]

Does incident work better for slide film? I've always used reflected for Slides.

Me too. I no longer shoot slides.

 

[Poisson Du Jour]

Does incident work better for slide film? I've always used reflected for
Slides.

When you know what you are doing (and why!), incident metering works well with transparency film just like multi-spot metering: they both have important uses and known outcomes in specific circumstances. I use incident for backlit subjects or mixed frontal light; multispot is for getting the full picture of tone/contrast variations across the scene e.g. the broader landscape/scenic. One important point is to match the meter's read steps (0.5, 1 or 0.3) with the known (not assumed) latitude of the film and work within that range.

 

[Diapositivo]

Does incident work better for slide film? I've always used reflected for
Slides.

Incident light measuring works very well for slides provided your subject brightness range is not such as to force you to make choices about what can be seen in the picture, and what will be lost.
If the SBR does not pose problems, incident light gives you very good results and is fast and practical (provided you can place the dome in the same light as the subject).
If the SBR calls for troubles, then I prefer spot reflected light metering, deciding which high light do I need to preserve, placing it 2.7 or 3 EV above the reading of the light meter (depending on film. You can trust Astia with 3EV above light meter reading, in my experience, 2.7 is safe in general) and letting the shadows fall where they may.
Trouble may arise with marble façades in full sun and situations where you want to be careful not to lose texture in the highlights, and nocturne pictures.
For general subjects, the incident light meter is actually my preferred way to go with slides. That saves from the hussle of finding a "middle grey" in the subject and asking yourself is it really middle, 12%, 18%, should I place a grey card, etc. Incident light measuring just works fine.

 

[shutterboy]

RobC

18% reflectance is the middle of a 5 stop range and slide film accepts approx a 5 stop range.
18% reflectance is not the middle of a 7 1/3 stop range which is what black and white film standard works to and pretty much colour film too.
Until people understand the difference between film which is not a medium we take reflectance readings from and that the reflectance meters aim to put the exposure in the middle of the film curve more or less and which is nothing to do with 18% then people are not going to understand that 18% reflectance is meaningless to exposure.
A kodak grey card is just over 1 stop lighter than the middle of a 7 1/3 stop range which is what current black and white film standard works to.

I was reading through this and also looked at http://www.sekonic.com/whatisyoursp...dts-software-profile-your-digital-camera.aspx. I believe it was suggested that the incident and reflected readings of the 18% gray card should match. Or, do I get it wrong from the video? I have read your earlier response and I *think* I understand the 5 stop vs 7 1/3 stop argument.

 

[RobC]

The video clearly shows that in his test the reflection and incident meters differed by 0.3 of a stop.

The generated graph over a dynamic range of 5.9 stops says his mid point is 2.8 stops below his high point. So it follows that the software has worked out its own K Factor which in this case would be close to 12.5%. This is becasue its very close to the middle his dynamic range of 5.9 stops. So the K factor relates to the mid point of the dynamic range being considered. So in this case the K factor = 100*12.5% = 8. So approximately 12.5% reflectance card would be suitable for 6 stops range, but only if your meter was using a K=8, otherwise if it were using a K=12.5 it would be approx 1/2 stop out.

For 7 1/3 range it needs to be a higher K Value (lower %age) to hit the middle of the curve. Hand held reflection meters being designed mostly for film, are based on the longer expected dynamic range or 7 1/3 stops.

Clearly, if K = 12.5 (8%) in his example then it would miss the middle of the curve by about 1/2 a stop instead of less than a third or a stop. Which only goes to show that K isn't a constant which would cover all meters and dynamic ranges if it were. It takes the expected dynamic range of the medium into consideration.

I guess some of the meters designed for digital cameras could be calibrated with your own meter profile if you can get the data from film or print into them. Then you don't need to worry about what any of the percenatges of K values are. You can just create a profile for each film type and select it.

 

[markbarendt]

The video clearly shows that in his test the reflection and incident meters differed by 0.3 of a stop.

The generated graph over a dynamic range of 5.9 stops says his mid point is 2.8 stops below his high point. So it follows that the software has worked out its own K Factor which in this case would be close to 12.5%. This is becasue its very close to the middle his dynamic range of 5.9 stops. So the K factor relates to the mid point of the dynamic range being considered. So in this case the K factor = 100*12.5% = 8. So approximately 12.5% reflectance card would be suitable for 6 stops range, but only if your meter was using a K=8, otherwise if it were using a K=12.5 it would be approx 1/2 stop out.

For 7 1/3 range it needs to be a higher K Value (lower %age) to hit the middle of the curve. Hand held reflection meters being designed mostly for film, are based on the longer expected dynamic range or 7 1/3 stops.

Clearly, if K = 12.5 (8%) in his example then it would miss the middle of the curve by about 1/2 a stop instead of less than a third or a stop. Which only goes to show that K isn't a constant which would cover all meters and dynamic ranges if it were. It takes the expected dynamic range of the medium into consideration.

I guess some of the meters designed for digital cameras could be calibrated with your own meter profile if you can get the data from film or print into them. Then you don't need to worry about what any of the percenatges of K values are. You can just create a profile for each film type and select it.

Actually there are variables that aren't apparent or accounted for by the meter, specifically the internal processing profile in the camera.

To make a JPEG file the camera has to process the raw data and output a finished image, this is akin to darkroom work with a negative including contrast adjustments, burn and dodge and more. The shooting profiles are proprietary (Canon's is different that Nikon's is different than ...), adaptive (can auto-adjust for contrast and ...), customizable (can be set manually) and are myriad even in a single camera (for example on my D200 I can switch preset profiles or adjust specific settings on the fly. These profile choices affect how all the tones are rendered in a JPEG.

In a camera's default mode if the testing crew had turned 180 degrees and shot the test card in full sun instead, it is highly likely the test would have delivered a completely different result. Turn 90 and shoot cross-lit and gotten yet another set of results.

 

[Diapositivo]

I have read your earlier response and I *think* I understand the 5 stop vs 7 1/3 stop argument.

That's in fact what I struggle to understand. I see no link at all between scene range and use of light meter.

The basic idea if I get it right is: if one extreme of the range is 100% reflectivity, and the other extreme is somewhere on the shadows, at different EV distance, then the "average grey" of the scene will fall at a different degree of reflectivity according to the range, and the larger the range, the lower the average grey of the scene, assuming one extreme of the range always is 100% reflectivity.

To which my doubts are:

- why the assumption that the highlight extreme of the range is kept constant, and the different scene range would only impact the lower end of the range, the shadows? Different scenes can have 4, 6, 10, whatever EV of range and still be centered on the same grey, whichever that grey is. (Actually one might argue that, in general, the average grey of the scene is likely to fall near "middle grey" regardless of the range of the scene. Only for "high key" or "low key" images the average tone is much above, or below, middle grey).

- what has this to do, in general, with the light meter? The reflected light meter meters a certain light (luminance) and, given an implied reflectivity (of 18% I presume) and therefore given a certain implied subject "shade of grey", gives the right exposure to create, on slide, that implied subject shade of grey. The circumstance that, in your actual scene, that shade of grey corresponds to the average grey, or is below the average grey of the scene, or above it, should not change a jota in the way you use the light meter. Actually it does not change even if the metered spot is not middle grey at all. You measure and then you "place". You measure white and then you "place" white, e.g., by adding exposure to the grey value the lightmeter gives.

It seems to me that the light meter "places 18% grey on the slide film" regardless of the scene: its average reflectivity, its range, its being low-key or high-key etc. are not in cause. Whatever luminance you feed into the light meter, it chews it and spits back an exposure value to create an 18% (or whatever it is calibrated for) grey on your slide film.

The "exposure choice" that the photographer necessarily makes in the various scene conditions (depending on the scene, on the film used, exposing for shadows, for highlights etc.) comes after the reading from the lightmeter, and it's a different and subsequent logical step.

The reflected light meter knows nothing about that. The light meter lives in a simple world with only two factors: luminance, which is variable, and a certain shade of grey, which is kept fixed.

 

[markbarendt]

That's in fact what I struggle to understand. I see no link at all between scene range and use of light meter.

Nor should you.

The meter suggests a camera setting based on film speed.

 

[DREW WILEY]

If film has enough linearity to its response to light, then YOU decide where to place the exposure based upon how you want that image recorded. This
is ideally done with a spotmeter, where you compare the relevant readings. I sometimes shoot scenes where there may be over twelve stops of range. Obviously, this requires not only black and white film, but particular films with very long straight characteristic curves. In softer lighting, the
rules change. Then with color film, one must prioritize what part of the subject deserves saturated hues, and what can be sacrificed. Or more likely,
we learn to hunt out the kind of lighting which flatters our preferred color film in the first place. Ultimately, your light meter must be your own ability
to THINK. For example, different hue saturate at different reflectance values. And color in nature are complex. You must learn through testing or
experience what corresponds to the mid. Otherwise, carry a gray card. With black and white film, everything is relative. You establish your own high,
low, and mid parameters, based on the specific film and how you want to interpret the resulting negative or chrome. If all this sounds too complex,
then simplify, and standardize on one standard film and meter, and just practice until it's a subconscious process. This is how it was done before light
meters were ever invented yet.

 

[markbarendt]

Obviously, this requires not only black and white film,

Actually I disagree, I find C41 color films fully capable of dealing with very high contrast scenes with a caveat, one must be willing to burn and dodge. If that compromise is acceptable then controlling the look of the color, darker/more saturated or lighter/more pastel is very doable.

What B&W can do better than color is straight print a 12-stop scene.

 

[shutterboy]

The video clearly shows that in his test the reflection and incident meters differed by 0.3 of a stop.

Yes that is true. But I assumed, as you had explained earlier, it should have been 1 stop apart since the meter was uncalibrated, no?

Clearly, if K = 12.5 (8%) in his example then it would miss the middle of the curve by about 1/2 a stop instead of less than a third or a stop. Which only goes to show that K isn't a constant which would cover all meters and dynamic ranges if it were. It takes the expected dynamic range of the medium into consideration.

So, please help me understand this correctly. Assuming I am using a Sekonic L758-DR with a film that I have not done this exposure experiment with already, it is actually more consistent to erase all calibration settings and use factory defaults with K=12.5?

 

[markbarendt]

So, please help me understand this correctly. Assuming I am using a Sekonic L758-DR with a film that I have not done this exposure experiment with already, it is actually more consistent to erase all calibration settings and use factory defaults with K=12.5?

Yes, an alternate calibration could easily lead you astray.

The calibration software is essentially judging "finished positives" not negatives. All the finishing adjustments and choices affect the calibration.

 

[shutterboy]

Yes, an alternate calibration could easily lead you astray.

The calibration software is essentially judging "finished positives" not negatives. All the finishing adjustments and choices affect the calibration.

Okay. That is very helpful. Now, what about my first question? Why did the monitor not show a stop apart rather than just a third of a stop?

 

[DREW WILEY]

Hi Mark. I obviously did not mention color neg film because this whole thread is inevitably veering into various sub-directions already. But since you
brought it up, color neg film is not in fact simply a matter of dodging or burning (or in my case, preferably masking) to match the paper. And in this
particular discussion, we're concerned about metering to get the whole range onto the film in the first place. What long-scale color neg films do is sacrifice hue accuracy and saturation in able to bridge that span. The question is where and how. All of these wide "latitude" color films are primarily
engineered for pleasing skintones, so turn anything related into some similar mush or mud. It's a smart marketing decision, especially with amateur
color films, which are often poorly exposed. The idea is to get Aunt Sue's face to at least look realistic, even if nothing else in the scene is. To this day, Kodak's own flagship series allows us to trade off features, all the way from very soft Portra for portraits up to something like Ektar, with saturation but less forgiveness. Best leave that discussion for a different thread, except to state that I use Kodak's recommended box speed for these
kinds of films, and meter exactly the same as for chromes. What photographers have done over the years is subconsciously accept certain color neg
idiosyncasies as representing the real world. Pumpkin yellows and poison greens and warm cozy shadows, and everyone has nice unblemished skin.
And if they don't, a little vaseline on the lens cures that! Meanwhile, I'm out in the cold cruel world of Ektar, where shadows still look blue and zits
still exist!

 

[markbarendt]

Okay. That is very helpful. Now, what about my first question? Why did the monitor not show a stop apart rather than just a third of a stop?

If I remember them correctly the directions included with a Kodak gray card recommend a 2/3's stop correction. It also suggests a specific tilt to use the card. Other sources suggest no tilt.

IMO the exact offset one gets (0, 1/3, 2/3, 1) is dependent upon how the card is used. Gotta hold your mouth just right to get what anybody else gets.

 

[markbarendt]

What photographers have done over the years is subconsciously accept certain color neg idiosyncrasies as representing the real world.

Giggle.

"Velveeta" ruined our world!

I don't disagree about the differences between films. I do think of those differences though, more as differences in color palette. Each really seems to me to create a different set of colors.

The other thing I have found is that print exposure can help me make a Portra print feel more saturated, no I can't turn it into Ektar, but I can tip the scale a bit.

 

[Diapositivo]

Okay. That is very helpful. Now, what about my first question? Why did the monitor not show a stop apart rather than just a third of a stop?

It should in theory have given the same value.
See this:
http://dpanswers.com/content/tech_kfactor.php

If Sekonic meters are calibrated with K = 12.5 that's equivalent to a calibration to a 15.7% grey (see the table in the link above) which justifies a difference of 0.15 EV between the two measures. The other 0.15 might be due to other secondary factors: unevenness of lighting for instance, or wrong angle of measurement between light meter and test card, or a small shade projected over it, or simple miscalibration of the instrument. In fact, the person says that the software will recalibrate, if I get it right, the light meter, presumably to make it match the incident light reading.

Tests made in this thread suggest a 0.3 EV difference or so is what one normally gets. Nobody seems to get a difference of 1 EV between grey card and incident reading.

Light meters with K = 14 (Pentax, Minolta) should exactly match the grey card (according to the abovementioned table).

 

[DREW WILEY]

There are certain complex hues that I can bag with Ektar that I simply cannot with traditional color neg films. The nice thing about unsharp masking
is that you can tune up or tune down not only overall contrast, but certain hues selectively. It's a bit like power steering, so ya gotta be careful not to
overdo it. And you have to start with all the information on the correct part of the curve. That's why the ABC's of proper metering are still so important. Relying on "latitude" is poison. Treat Ektar with as much respect as chrome film and you'll have no problem. Pretend it's Kodacolor Gold and you've got a mess on your hands! Portra 400 is a nice compromise film between slow Portra and Ektar, but generally not as clean as I like.
Since I'm primarily a printmaker, even my attitude toward Velveeta was different. It's how something potentially translates into a print that counts,
not just how it looks on a light box! If all somebody wants is layers of jam and honey atop sugar cubes, they should just go full bore digital saturation until they gag.

 

[markbarendt]

Nobody seems to get a difference of 1 EV between grey card and incident reading.

Um, I do, and the OP does, and I know others that use 1-stop as their offset, not everybody by any stretch, but not nobody.

 

[Diapositivo]

Um, I do, and the OP does, and I know others that use 1-stop as their offset, not everybody by any stretch, but not nobody.

You are right. When this thread begun, I was convinced that a certain offset was normal. Now that I am convinced that a certain offset is the result of some mistake (either here or there), I forgot that the initial problem was a discrepancy of up to 1 EV.

This really begs the question of what's wrong with your/my equipment, though. This is something that should be pretty consistent in the photographic community. It cannot be normal that somebody has got 1/3 EV discrepancy and somebody else 1 EV. These are supposed to be precision instruments, very expensive at their time, for careful exposure. Ultimately things should sum up. It seems we are far from it.

Probably too much discussions about K factors and not enough reasoning about what could be wrong in light metering practice, I suspect.

Things that could be questioned are:
- Calibration of instruments;
- Right battery (1.2 V / 1.5 V), right battery state of charge;
- Quality of grey card or reflectance grade (some grey card might actually be not 18%);
- State of grey card (old, dirty);
- Inclination of card relative to instrument (mirror effects);
- Consumption of selenium cell for selenium light meters;
- Opacization of white dome (might have become yellow, or dirty);
- "Fatigue" of selenium meters (it appears they have to "rest" after some time in the sun);
- General quality of light meter (my Gossen Sixtino II is basically a joke and such was also when new);

 

[Diapositivo]

My setup: Hasselblad 501c, 80mm glass, Sekonic L-508 (has both spot and incident capabilities). My subject was a flower pot about 10' away from my tripod mounted camera, outside, under overcast skies (the light was omnidirectional, no harsh shadows). I take the incident reading with the diffuser dome up: 1/30th at 5.8, ISO 400. I take the 1° spot reading back at the camera (at 1°, the grey card not only covers the metering circle, but the entire viewfinder): 1/60th at 5.8, ISO 400.

So, am I missing something fundamental about using a spot meter? Or does my used-from-ebay-meter need to be calibrated? This is the first time I've used a meter (if that wasn't obvious!)

Can you please give the exact measurement you get in tenth of exposure value? (or tenth of stops).

When you say 5.8 I guess you mean 5.6. Or do you mean something like 5.6 + 0.2 EV? (f/5.6 + 2/10 of EV).

Can you confirm you have 1 full EV of discrepancy, e.g. 10/10 of EV when measure in 1/10th of EV increments?

I'm reading the instruction booklet of your instrument, quite a beast.
Did you observe the minimum distance of 1 meter when using the spot meter?

I suspect the right measurement in this case would be with the retracted dome. The card is a flat subject and does not capture lateral light.

If your light source is not frontal, does not face the card, the lumisphere is going to catch some light that the flat card is not going to reflect toward your lens. If your ligth source is exactly frontal, the lumisphere is going to average with some less intense lateral light. So I would place, for incident light reading, the flat disc (or recessed dome) in front of the subject.

Did you buy your light meter second hand? In that case, did you bring it back to factory calibration? (the previous owner, if any, might have calibrated it in order to respond like some other instrument he had).

Finally, did you use a fresh battery? Did you try with a fresh battery? It seems your light meter does not like NiCd or NiMH batteries. The manual says: manganese, alkaline, or lithium dry cell, this means it doesn't like low voltages. Maybe your battery is old, and has a low voltage.

The instruction manual says:
Lumisphere C = 340
Flat diffuser C = 250
K = 12.5

According to the old same table, that would give a calibration on a grey card of 18% with a discrepancy of 0.15 EV when using the flat diffuser.

 

[markbarendt]

You are right. When this thread begun, I was convinced that a certain offset was normal. Now that I am convinced that a certain offset is the result of some mistake (either here or there), I forgot that the initial problem was a discrepancy of up to 1 EV.

This really begs the question of what's wrong with your/my equipment, though. This is something that should be pretty consistent in the photographic community. It cannot be normal that somebody has got 1/3 EV and somebody else 1 EV. These are supposed to be precision instruments, very expensive at their time, for careful exposure. Ultimately things should sum up. It seems we are far from it.

Probably too much discussions about K factors and not enough reasoning about what could be wrong in light metering practice, I suspect.

I think that a significant portion of the difference is simply personal style and quirks, some is probably a precision error because of rounding up in that 1/2 or 2/3=1 in our heads, some may be equipment failure but I'd bet that is a small percentage of cases.

IMO the real magic of using a known target, like the Kodak gray card, is not that we are identifying a specific tone in the scene (because it's not really part of our scenes), but instead that when we understand our normal offset for that target then our spot meter can be used like an incident meter. Dunn and Wakefield in fact suggest that there is no practical difference.

In either situation: "gray card & reflective meter" or "incident meter alone"; a "distance" is defined (horizontally) by the film's speed point and the meter reading point which are real numbers on the X axis of the H&D curve, the "distance" from the meter reading point onward to the right is a variable because the slope of the curve is controlled by development.

 

[shutterboy]

Okay, I actually wrote to Sekonic and here is the response I got. My original email is also bottom posted:

Dear Mr. or Ms. Subhro Kar,

Thank you for your inquiry.
I am Minoru Oda(Mr) from Sales Operation Sec.
of light meter in Sekonic Corporation in Japan.

As you already might know, exposure value is determined by calibration constants.
Our light meter has K=12.5, C=340(Lumisphere), C=250(Lumidisc).
Therefore, the incident reading and the reflected reading(with 18% gray) are different under the
condition of point light source and in dark room. However, the reason you mentioned is a little
wrong.

These calibration constants means that if you measure 16% gray with spot, the reading might be
same as incident reading of lumidisc.
However, in the measurement with lumisphere, the lumisphere receives more light than Lumidisc
does.
It is no meaning to compare the readings between Lumisphere (incident) and Spot(reflected) because
they are different system and receive different light.
If forced to say, if you measure 11.5% gray with spot, the reading might be same as incident reading
of lumisphere under the condition of point light source and in dark room with no reflection from
walls.
However, actually in the lighting in nature or studio, "Point light source" are impossible.
So, this is only for theory and formula.
We have traditionally　continued to use C=340(Lumisphere) from long time ago, because we have
recommended it and our customer has appreciated its performance in nature or studio.

Does it answer your inquiry?
If you have any question, please kindly let us know.

Sincerely yours,

Minoru Oda
Sales Operation Sec.
******************************************************
SEKONIC CORPORATION
7-24-14, Oizumi-Gakuen-Cho,
Nerima-Ku, Tokyo 178-8686
Japan
Sales Operation Sec.

TEL: 03-3978-2317
FAX:03-3978-2144
Email: m.oda@sekonic.co.jp
Web: http://www.sekonic.co.jp
******************************************************


subhro@80386.org さんは書きました:
Date: Thu, 17 Mar 2016 15:15:19 +0900

=============================================
Subject : Support
Name : Subhro Kar
Email : subhro@80386.org
Company Name :
Division Name :
Country : USA
Zip Code :
Address :
TEL :
Product Name / Model Name : Sekonic L-758DR

Comment
------------------
Hello,

I am a film photographer and have recently read on a few websites and forums that the incident and
reflected readings of a 18% gray card from a Sekonic L-758DR can be different. The reason as
explained in the article was reflectance meters target middle of film curve (7 1/3rd stop) or more
precisely 8% (= 12.5K Factor), whereas incident meters will target the middle of a 10 stop wedge,
that is 18% reflectance (about 1 stop away from 8% reflectance). Is my understanding correct?

Thanks
Subhro
------------------

=============================================

 

[RobC]

which is exactly what we already knew