Different measurements with spot vs incident metering on same target?

[Sirius Glass]

Can I move on now and ask: under what circumstances might the spot meter produce a "better exposure than an incident meter which I think you mentioned in one of your earlier posts?

In high SBR conditions I use multiple spot readings of the highlights, where I would like the medium gray to be, and the darkest area that I still want detail. I then determine the exposure.

 

[DREW WILEY]

And please folks, don't confuse what meters do with Zone System technique. Apples and oranges. Learn to use a meter first, then if you want to
debate how many zones God created light in, do so elsewhere.

 

[RobC]

Thanks for that RobC. Can I also take it that the opening up one stop correction applies under any and all light conditions( accepting that in sunlight the angle of the card will be important)

Can I move on now and ask: under what circumstances might the spot meter produce a "better exposure than an incident meter which I think you mentioned in one of your earlier posts?

pentaxuser

Again a moot point. It depends on the combined subject brightness range of your subject, the development you give it and where you place it on the film curve by adjusting from the metered value and how you print it.

Keep in mind that your spot meter (which for the sake of argument uses K factor of 12.5) always adjusts down from what is metered by 3 2/3 stops then for that to be correct for a grey card you would in theory just meter the card and open up 1 stop. Simple except that if the SBR was 10 stops, when you come to print it it won't fit on the paper so you or lab will alter printing and that will put your grey card on some other tone. Who knows where becasue you don't know how you or they will do it.
So professional photographers will carefully balance the lighting of their subjects to get exactly the lighting ratios they know through experience will produce the best reproduction they know how to achieve. But if you just happen to be out and about without controlling lighting to suit the subject then you have to either control exposure and dev precisely and/or control printing a la the zone system or just get what you get. Its not an exact science unless you approach in a 100% controlled way which is what the zone system attempts to do.

With colour I'm sure you are aware that exact colour reproduction is very difficult to achieve outside of the studio or very controlled environment. So all I can give you is ball park advice to meter card and open up 1 stop and how it prints depends on EI, SBR, dev and how you print it. But by and large if you place the grey card in the part of the subject you want best colour reproduction then metering it and opening up 1 stop will get you closish.

AND

if you happen to be using slide film then I would just meter the card and use the expsoure the meter gives you without altering it unless you know better through experience with any particular film, they are not all the same.

AND

If you use your spot meter to get the total SBR range and say its 9 stops and you specifically want to get the shadow end of the SBR to be properly exposed, then you can meter the darkest part of the subject which may be almost black in the knowledge that the reading would be 3 2/3 stop more than that requires and close down 3 2/3 stops to get it exposed exactly as it is. You couldn't do that with an incident meter unless you walk over and meter only that section. But to be able to do that and make the right choice you would need to know the SBR of your subject and an incident meter doesn't tell you that unless you walk around your whole subject taking different readings which simply isn't viable in some circumstances, especially with distant subjects. So a spot meter has advantages but you must undestand exactly what its telling you and what you film is capable of and how that matches up with your printing. And that is what the zone system is all about.

AND

if you were using zone sytem and calibrated your dev for 10 stop range then an incident meter would not give a reading putting the exposure in the middle of the curve becasue its calbrated to adjust for the standard 7 1/3 stop range. Without knowing waht the SBr of the is you wouldn't know how much to adjust by. A spot meter allows you to determine this. same as above but put a slightly different way.

 

[Old-N-Feeble]

There's a reason Kodak calls it an "18 percent gray card" and not a "middle gray card" or "Zone V card". Just remember to overexpose one f-stop if you meter from an "18 percent gray card" and don't worry about complex formulas. Better yet, spot meter off the various "important" areas of the subject itself and learn where to place those values. You'll also need to have a good understanding of how your light meter (and film) respond to various colors of the light spectrum.

 

[RobC]

There's a reason Kodak calls it an "18 percent gray card" and not a "middle gray card" or "Zone V card". Just remember to overexpose one f-stop if you meter from an "18 percent gray card" and don't worry about complex formulas. Better yet, spot meter off the various "important" areas of the subject itself and learn where to place those values. You'll also need to have a good understanding of how your light meter (and film) respond to various colors of the light spectrum.

I think we're on the same wavelength.

 

[RalphLambrecht]

OMG we're into another AA argument. I'm opting out as I've been here to often and it never ends pretty. Just accept everyone has their own interpretation.

You are entitled to your own opinion but not to your own facts

 

[RalphLambrecht]

Do you meter still or do you take photographs already ??

I don't measure;I justfix it in Photoshop

 

[RobC]

You are entitled to your own opinion but not to your own facts

which fact and would you like to give a reasoned explanation.

 

[macfred]

I don't measure;I justfix it in Photoshop

Honesty is the best policy ...

 

[DREW WILEY]

Isn't fixing it in Photoshop the work of a mortician?

 

[Diapositivo]

A good learning thread is this one for me. To continue with this practical learning theme let's assume that I only have a spot meter and a Kodak grey card but want to get the same accuracy in metering as given by an incident meter. For simplicity lets assume that it is overcast conditions and I can ignore getting the angle of the card right and the scene is a 71/3 stop range.

In practical terms what do I need to do after spot measuring the grey card to get the correct(a la the incident meter) exposure ?

Thanks

pentaxuser

I offer you my understanding of the matter.

It depends what you meter for. Let's say that you meter for an exposure on negative film, and that you are content with placing the middle grey on the scene (the supposed 13% reflectance stuff) on the middle grey of your film, then you would behave the same regardless of the range of the scene: 7, 8, 10 or 4 stops of range does not make a difference. The reading of the grey card (with the correction stated above) will make the middle of the scene (the average grey) to produce on the film the density that the producer (or the sensitivity determination method) defines as the density more appropriate for middle grey. We can approximate this as "middle density": in that case, that exposure will place the middle grey of the subject in the "middle density" of the film curve.

I don't use negatives so somebody else will elaborate more on "middle density" of a negative, which probably is quite a moving target depending of how you plan to develop and print your negative.
Basically, given a certain ISO sensitivity of your film, exposing the middle grey of the scene with the lightmeter will make that grey fall exactly where the film producer expected you to to normally want it to fall.
(That's not necessarily the way you want to expose your negative, as said).

So in this scenario you cannot ignore the angle of the card right, and you cannot ignore that the card is lighter grey than the average of your scene (probably, I mean, if the average of your scene is actually average), but you can ignore the range of the scene because "middle" is in the middle. Again, that's what I grasped, but I am a slide guy.

(As a side note, negative has such a latitude that you can actually forget light metering at all and you will probably get a printable negative, but that's another story).

Let's say you meter for slide film, and let's assume your slide film has 6 EV of good detail, good texture. Let's assume you have 3 EV above middle density and 3 EV below middle density of good texture in your film. Above and below that interval, texture suffers (gradually blown highlights, gradually blocked shadows).

You have measured your scene and you have meaningful detail of your subject in a 7.3 EV range. Your blanket is shorter than the scene you want to cover with it, because you only have 6 EV of good detail, good texture, but your scene ideally would ask for 7.3 EV of good texture.

In this case, either you change your scene, or you change your lighting, or you make some compromise. Let's say you make some compromise: you must choose the 6 EV of the scene that you want to retain with the highest quality (detail, texture), and you accept some loss of detail in the remaining range.

Exceptions aside, let's make the normal case: with slides you normally don't want, above all, to blow the highlights. You want to preserve, or protect, the highlights - keeping the texture of the subject on the final image - and let the shadows "fall where they may". You know you will lose some detail in the shadows. The "toe" of the film curve will make the detail loss to be gradual.

You meter with your (reflected light) spot meter the highlight part of your subject. (Not the grey card). The highlights that are meaningful and for which you want to preserve texture. Now let's introduce a little, common complication and let's say this highlights of the scene is something very white (snow, marble, sugar...). You know that at the extreme range of white you cannot have good texture (by definition, white is white is white, no room for texture on the film when you reach pure white), you want texture, you push it a little bit toward grey.

You "place" your highlights. Instead of placing them 3EV over the middle grey, you place them 2.7 EV over the middle grey - to be sure to preserve texture on your white subject).

You meter the highlights and the meter tells you: 1/125 - f/16. That is the exposure that would make the whitest of your subject appear "middle grey" on your slide. You open 2.7 EV. So you set 1/125 f/6.3.

The reading you obtain from your spot meter on the highlights takes into account both the incident light and the reflectivity of the subject. That is the only way you can "place" the highlights on slide film. Measuring incident light (or reflected light on the grey card) does not allow you to "place" the highlights because you don't know, exactly, how bright is the subject and where it will fall on your curve (inside, or outside, the range of good detail).

You use incident light metering (or grey card with the caveats) "only" when you know, in principle, that the brightness range of your subject is not such as to create problems to the dynamic range of your film.

Incident light metering is very good and very fast for uncomplicated situations. It is not fool-proof because it does not take into account that that white cat is very white and the fur can appear without texture in the final image.

If your scene is more than 6 EV, and you shoot with slide film, you will normally want to preserve detail in the highlight and you will "place" the highlights and you'd better do this by directly measuring the highlights with a spot reflected light meter.

If you shoot with negative film, you have a lot of dynamic range and you can place your entire scene higher or lower on the curve of your film, depending on your printing needs.

My two cents, and YMMV especially regarding the use of density of your negative.

PS Maybe I misunderstood your question. The answer in that case is: you meter the grey card, and you open half a stop. That's because grey card is 18% and the middle grey used in photography is around 12%, as said in another post.

 

[DREW WILEY]

Just take your damn meter and go out and shoot a typical scene. Bracket if you must. Then try to print it, or whatever. Why make things so damn
complicated? Yeah, I own several spotmeters, have film densitometers, plot with them, and think the Zone System is a Kindergarten rite of passage
to real sensitometry. But I also know I grew up with a primitive exterior-coupled CDS averaging meter on an early Honeywell Pentax, routinely shot Kodachrome in harsh mountain lighting, and never goofed an exposure! Competence comes with practice.

 

[RobC]

given there is no standard for how much print exposure is required to reproduce a grey card, then any standard that says a grey is a middle grey is pretty meaningless. It is just a mddlish grey which you can calibrate your system to if you so wish. There is nothing that says a film should reproduce a grey card at a certain film transmission density. There is nothing which says a grey card will be the exact middle of a film curve produced in the ISO test of that film.
Given the lack of all these things it should be clear that a grey card is simply a middlish grey that you calibrate your system to if you so wish but has no link to a light meter unless you choose to make that link by calibrating your system to it.
And it's a claimed to be a Munsell middle grey which had nothing to do with what an average subject reflectance is.
And if its an average value of the average scene then by using it all you are doing is turning your spot meter into an averaging meter. The whole point of a spot meter is to meter actual values of the subject and not to use an average reading. You may just as well use an incident meter which will give you a more accurate reading if you are doing that. And incident meters aren't designed to meter reflectance so why would anyone compare the readings of an incident against a reflective meter. If you expect them to always give the same then why use one instead of the other.

 

[Xmas]

OMG we're into another AA argument. I'm opting out as I've been here to often and it never ends pretty. Just accept everyone has their own interpretation.

There are things in life that it is too difficult to explain.
There is the same difference between black and white paint as between grey and grey paint, ie two different grey paints.
They are all shades of 'neutral colour'.
And they can fade in sun light or change in time.

The grey card that Kodak sold or the one that I bought from Kodak was sold with a colour wheel filter set for colour balance tests when taking photos or while fine adjustments during colour printing.

I took one to weddings and got a brides maid to hold or hide during shots.

I had a Weston dome on brides nose.

 

[itsdoable]

Unless something has changed drastically in the years since I was shooting studio, and incident meter reads the same as a reflected meter off an 18% grey surface (or 16% if you are anti-Kodak). That is how it is calibrated. Neither have any idea of what the subject's colour or shade is, it is a measurable, repeatable calibration. What you do with the reading afterwards to get your center grey / desired zone / push-pull processing / etc... is up to you.

As to why the OP's readings are different, there are several possible reasons. The grey card measures reflection off a flat surface, the incident "dome" simulated a 3-D surface (use the flat un-dome attachment in the same plane as the grey card if you have one). The grey card is usually a printed paper product, which is prone to fading and specular reflection (good grey cards are not cheap). Incident domes yellow over time.

 

[RobC]

another thread on same topic...

(there was a url link here which no longer exists)

 

[Ian C]

I did a simple comparison of the incident and reflected-light readings from 3 different gray cards using my Sekonic L-508 meter. The meter has never been adjusted since I purchased it new.

Cards A and B were well-used generic cards that show some wear to the reflective surface. Card C was a new Delta 1 gray card. I was careful to place the meter so that it would not get a strong “hotspot” reflection from the surface of the cards. Compared to the incident readings I got the following reflected readings:

Card A: + 0.3 stops

Card B: + 0.2 stops

Card C (Delta1) gave readings that varied from 0.0 to -0.1 stops. Possibly the reflected light intensity was close to the middle value – 0.05 stops. Of course, the meter can only display values to the nearest 0.1 stop, hence the variation among successive readings.

Some gray cards likely vary more than the small sample I tested.

 

[RobC]

for an incident meter to to give is supposed 12% reading the light source must be on its axis (so not pointing at camera) and the spot meter must be perpendicular to the grey card.

 

[RobC]

And people go on about there being diffuse light so the angle of the grey card doesn't matter but even in diffuse light if you tilt the card you can see with your own eyes it changes colour and its so easy to test this with a meter. But meter should be perpendicular to it for this meter comparison test from what I've read.
But I still believe that because K factor is used as a divisor which equates to 8% that the figures for 12% or 18% don't make sense. And again, there is no standard for what the film transparency density should be or at least I've never read or heard about one, so its all moot anyway.

 

[Poisson Du Jour]

My question: why am I getting two different meter readings when I take an incident reading of my subject, and then a spot reading off a grey card at my subject? I'm consistently getting differing readings of one full stop difference - with the spot metering off the grey card metering one stop less than incident.

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!)

Yes, something is missing!
A spot meter is only used with a grey card to lock in a known mid-tone reading in the absence of being readily able to identify one in the scene\. Once that mid-tone reading from the grey card is locked into the meter, additional readings of the scene are taken and then averaged around the mid-tone reading. Since a grey card is already a mid-tone, a single spot meter reading from it is meaningless without additional metrics to tell the meter about the variations of tone spread across the scene (from brightest but not pure spectrals, to darkest, but not rich blacks).

It is incorrect technique to aim the spot meter back at the camera to take a reading. It is always read aimed at the scene, and actually "swept" over the scene, reading variations of brightness (displayed in the viewfinder as you work), rather than an incident reading suggesting the scene is 'average' when it is most unlikely to be. I think you should get your hands on an instruction manual for the Sekonic and thoroughly read through the technique required to correctly use the meter and its benefits. In skilled hands, a meter (any meter) is an invaluable tool, very especially a multi-spot meter over incident (but both have their qualified uses and weaknesses).

 

[RobC]

Hi all,

Apologies if this doesn't quite fit in this forum; I figured, though, it's a question that might be helpful to some future medium format shooter...

My question: why am I getting two different meter readings when I take an incident reading of my subject, and then a spot reading off a grey card at my subject? I'm consistently getting differing readings of one full stop difference - with the spot metering off the grey card metering one stop less than incident.

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!)

To OP. Please try the following:

Take your grey card and orient it so it faces directly at the primary light source(not the camera). Then take your incident meter and using the flat disc (NOT Dome), put it infront of grey card and point it directly at the primary source(not the camera) and take a reading.
Now take your spot meter and with the grey card still facing directly at the primary light source, meter the grey card with the spot meter lens axis perpendicular to the grey card. i.e. straight in front of it without casting a shadow on it.

Now tell us how the readings differ.

And anyone else with a spot and incident meter can try the same and report back too and then maybe we can get a definitive answer about what's going on.

And yes I know everyone says point incident meter at camera but for this test please point incident meter with flat disc(not dome) at the primary light source.

 

[Diapositivo]

I can't make the experiment RobC suggests because my incident light meter only has the dome (no disk: Gossen Multisix, dome in front of the cell: incident light reading with 180° angle; dome away from the cell: reflected light reading with 30° angle of reading).

Anyway, sunny day, side of the building in shade. Grey card lighted by the sky, placed slightly toward the sky (almost vertical but not totally vertical).
Incident light measuring with dome: LV 11.2 or 11.3
Reflected light metering on the card: LV 11.8.

The card was at the height of my head and my arm did not throw any shadow on it.

That seems to give that 0.5 EV or slightly more of difference that is consistent with old time Kodak instructions and with the theory of light meters being calibrated for 12% reflectance.

Sorry I can't make the test with the disc.

Anyway considering that the light source was the entire sky, a diffused light coming from "all directions" so to speak, there should be no great difference between dome and disc, I think.

I look forward for somebody to report the results of the test suggested by Rob.

 

[RobC]

I can't make the experiment RobC suggests because my incident light meter only has the dome (no disk: Gossen Multisix, dome in front of the cell: incident light reading with 180° angle; dome away from the cell: reflected light reading with 30° angle of reading).

Anyway, sunny day, side of the building in shade. Grey card lighted by the sky, placed slightly toward the sky (almost vertical but not totally vertical).
Incident light measuring with dome: LV 11.2 or 11.3
Reflected light metering on the card: LV 11.8.

The card was at the height of my head and my arm did not throw any shadow on it.

That seems to give that 0.5 EV or slightly more of difference that is consistent with old time Kodak instructions and with the theory of light meters being calibrated for 12% reflectance.

Sorry I can't make the test with the disc.

Anyway considering that the light source was the entire sky, a diffused light coming from "all directions" so to speak, there should be no great difference between dome and disc, I think.

I look forward for somebody to report the results of the test suggested by Rob.

What I've put in bold is wrong. The disc is NOT just metering a narrower area. The disc uses a different C Factor than the Hemisphere does so it will give a different reading in identical lighting when using a modern Sekonic meter. I can't speak for other meters since I have no idea how they are calibrated and what values they use for K or C except my Minolta spot meter which I know uses K = 14 and the formula it uses.

Basically the Hemishpere is for general purpose photography and equates to approx to 12% reflectance whereas the disc is for comparing lighting ratios and equates to approx 16% reflectance. BUT NOTE THE USE OF APPROX. That is theory but reality never matches theory and it depends on exactly how each of the meter manufacturers implement it etc etc etc. AND how well the meter is actually adjusted to give the readings it is supposed to.

AND old meters may well be setup to give readings based on older standards. It is important to remember that most photography meters are not telling you a pure reading of how much light there is. They are telling you a corrected adjustment from how much light there is based on some photographic standard which is variable on the particular standard and quite possibly the type of film and the meter manufacturers interpretation from their own testing.

So basically you should only expect to get very close readings between a spot meter and your incident meter when card is facing light source at correct angle, incident meter is using flat disc and not difuser dome, and incident and spot are using equivalent c and K factors. (assuming a modern sekonic meter)
In other words, they will never match exactly except by pure chance. They will be closest when using flat disc.

 

[RobC]

Having said all that above, the situation is still that with a modern reflection spot meter, the formula used (at least by minolta) seems to take whatever is read and reduce it to 8% of that reading to place it 3 2/3 stops down from what is read which is somewhere near the middle of the film curve where there is no standard of what the film density should be. So its all moot about any reflection density reproducing any particular colour value. Its ball park depending on a lot of other variables, especially development. That is why we test to find out waht works best and through our experience we adjust to suit what we prefer. It ain't an exact science unless you're doing it in a lab for purpose of lab testing which never reproduces what we get out in the field.

 

[RobC]

And for pentaxuser,

If you had blazing hot direct sun on a subject which also had some very deep dark shadows such as inside a cave and you were stounding outside, then your incident meter if it were outside in the sun would underexpose whats in the cave and if it were in inside the cave and not in the sun it would overexpose whats outside the cave. But without knowing what the actual SBR was across the whole subject you wouldn't know where the optimum place to take a reading from was without going into the cave and taking a reading and going outside the cave and taking another reading and then doing the calcs based on the two readings.
Far easier with a spot meter to be able to stand at camera, decide what you want exposed optimally and take one reading and adjust to place on the tone you want using the zone system (except you need to do the leg work on how to accurately use the zone system in the first place). So they both have their pros and cons.