18% Grey Card. To use it or not.

Last night was a supermoon, I think that's unusually bright

Chuck1 said:

Last night was a supermoon, I think that's unusually bright

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Thanks!

Colloquially, supermoon means a full moon when the moon is at perigee. This makes it roughly 1.14x larger in diameter than when it's at apogee, and about 1.07x larger diameter than average. (In other words, it's not that super.) You square the diameter to get the ratio of its luminosity, so the Moon at supermoon provides about 1.14x more moonlight than an average full moon. https://en.wikipedia.org/wiki/Supermoon#Appearance

But, the surface brightness of the moon (luminosity per area) is the same at supermoon as at any other full moon. It's the same distance from the light source, which is the Sun. It's only brighter in total because it's bigger in the sky. If you are correctly measuring the surface brightness, you should get the same answer.

A reason the measurement is probably fairly variable, even if you are correctly photometering per area, is that the Moon's surface is non-Lambertian in its reflectance; unlike an ordinary diffuse reflector, it has a peak in its scattering function at 180 deg backscatter. (I mentioned this angular dependance of reflectance in this thread, several pages back.) This is why the full moon is more than 2x the total brightness of a half-illuminated moon (quarter moon).

Edited to add/clarify: IOW, the full moon's surface brightness should be somewhat higher in the center than the edge / limb. The numbers people have been quoting may be averaged over the disk, I don't know.

arturo_rs said:

A found in a box a 18% grey card and it made me think this:

Nowdays with digital cameras we can do almost everything but with film...things change.

A have a Nikon F100 and I shoot photos using the matrix mode. Until now, it works well for me but, can we improve the technical quality of the photos?

I tried spot metering using the 18% grey card and more than 50% of the takes are 1 stop under or overexposed if I use the matrix mode.

From your knowlegde and experience, does it matter? I mean the fidelity of color, grain, etc... Exposure affects the density of the color layers, so, it must be important, right?

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Nikon matrix metering is hard to beat in my experience.

Thanks reddesert. I used an SEI Photometer which is a comparison spot photometer, you adjust the brightness of a spot in the field of view until it seems to disappear. The spot is smaller than the moon.

It might be the air was clear. I repeated the measurements twice, and they were identical.

xkaes said:

I'm with Chan on this one. Gray cards have their usefulness, but with a spot meter??? or Matrix metering???

If you want accurate metering, get an incident meter -- which is not influenced by the reflectance of the subject.

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Right from when I started photography in 1963 I have never managed to get on with incident light readings. At work we had a Weston Master 1V Then a Lunasix then another Lunasix. My boss who started me off used reflected light of grass, or the back of his hand and he will never went wrong. By 'eck he was right. He learned his trade as a RAF photo reconnaissance pilot in Spitfires during the war so he had to know what he was doing.

I use a Minolta Autometer 3 now with a 10 degree spot but still the back of my hand when I am with my TLR, but always the matrix metering on my F6 - that does not make many mistakes.

A gray card (used correctly) will give you a correct exposure. It will be the same as an incident meter if both are in the same light. The problem with both is when the subject is in different light. You need to either move the incident meter or gray card into the same light -- or use a spot meter aimed at something that is 18% reflectance under that lighting. Each approach may or may not be easy in any situation. Using the palm of your hand has the same problem.

Plus, the palm of my hand is not the same as a my gray card -- but I can use it because I know how much to adjust (easy to figure out if a reflectance meter is all you have). But if you don't have a incident meter, just place a white Styrofoam cup (preferably empty) over your reflectance meter's cell and point it where the camera's lens will point.

BMbikerider said:

Right from when I started photography in 1963 I have never managed to get on with incident light readings. At work we had a Weston Master 1V Then a Lunasix then another Lunasix. My boss who started me off used reflected light of grass, or the back of his hand and he will never went wrong. By 'eck he was right. He learned his trade as a RAF photo reconnaissance pilot in Spitfires during the war so he had to know what he was doing.

I use a Minolta Autometer 3 now with a 10 degree spot but still the back of my hand when I am with my TLR, but always the matrix metering on my F6 - that does not make many mistakes.

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Interesting, your comment about incident metering not working for you.

• The darkness of the back of the hand varies during the year for many (relative to 18% gray as a constant), due to tanning. In fact, even the PALM of my hand, which most photographers cite as much more non-variable and inherently closer to 18% gray in brightness (than the back of the hand)...the plam of my hand is sometimes the same as gray card yet it can also be 0.3EV brighter than a gray card at some times in the year.
• The darkness of green grass varies (relative to 18% gray as a constant) not only due to variety of grass species but also due to the presence of reflective surface moisture on the grass blades

...proven to me by personal testing over time, not merely the claims of others.

My incident meter readings have consistently matched my one-degree spotmeter and my digital camera readings (and the histogram of the resultant shots, even shots of 18% gray test target surfaces). Tests conducted over the period of many decades of photography. I agree with comments by @xkaes

xkaes one cannot use a gray card correctly. wiltw knows. It’s very difficult to get repeatable results with one.

But that’s not going to stop me from trying.

I’ve had a two-tone “Minor White” target for years and it was faded badly, so I repainted it.

The two tones are meant to read on an exposure meter as one stop apart.

The two tones could be anything as long as they read out a stop difference. Copied from a Sekonic test target that has seven patches around 18% in sixth stop differences. The tones I picked are 25.5% and 12.7% reflectance. This is a half stop below and above 18%. In terms of density I was shooting for 0.90 and 0.60 which is obviously 0.30 apart and should meet the requirements.

When the densitometer said I met the specifications the exposure meters disagreed. So I held the 0.90 and increased the reflectance of the lighter side of the target taking half milligrams of black out of the mix, painting, waiting fir it to dry and trying again until the meters showed a full stop.

I had to go down to 0.56 on the light side.

Still, to see a full stop difference I need to aim down to minimize sheen. When I do that the Sekonic L-758DR will show between 0.9 to 1.1 stop difference. Not reliably a full stop.

Anecdotally we’ve said that an incident meter would agree with a spotmeter reading from a 12.7% reflectance target.

Even with this target I cannot replicate that story. It’s not agreeing.

xkaes said:

A gray card (used correctly) will give you a correct exposure. It will be the same as an incident meter if both are in the same light. The problem with both is when the subject is in different light. You need to either move the incident meter or gray card into the same light -- or use a spot meter aimed at something that is 18% reflectance under that lighting. Each approach may or may not be easy in any situation. Using the palm of your hand has the same problem.

Plus, the palm of my hand is not the same as a my gray card -- but I can use it because I know how much to adjust (easy to figure out if a reflectance meter is all you have). But if you don't have a incident meter, just place a white Styrofoam cup (preferably empty) over your reflectance meter's cell and point it where the camera's lens will point.

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I think the light levels in UK are pretty well more constant than the area you live in so it is easier to balance. For what it is worth the 'poor mans 18% grey card' can be reproduced from the inside of a breakfast cereal box, but the back of my hand is as good as, and has stood me in good stead for over 60 years. I have no need to change my method, If it ain't broke don't fix it!

An incident meter will give you an average reading, but if there are very bright or dark areas that will be outside of the film latitude range and capability, one has to be sacrificed to record the other. I was brought up with the saying 'Expose for the shadows and let the highlights take care of themselves'

That has definitely not changed. Do you not think some of us as photographers get their proverbial knickers in a twist trying hard to get the perfect exposure when everything is nearly always a lot simpler than that. I have given up worrying and just get on with it.

The best gray card is the dome of the incident meter. But there is known trick to meter shadows or highlights.

Always works!!!

With Sekonic L-758DR in my garage door test location at the northwest side of the house target lit by the sun wall in the shade…

In the shade, spotmeter reading of the light 25.5% target matches the incident reading with dome (3D) which sees more sky when it’s up and 12.7% reflectance matches with dome retracted (flat) because the sky is shaded. Incident reading changes by a full stop depending on on whether the dome is up or retracted.

In the sun, the dome and flat readings are both the same and match the dark 12.7% reflectance target.

RalphLambrecht said:

Nikon matrix metering is hard to beat in my experience.

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Agree. I have found it far more repeatable and accurate than any hand held meter I have used. Especially the later Nikons that incorporate the subjects colour into the metering algorithm.

In Bill's example shot, it's easy to take a reading of the sunlight & shadow sections -- whether using a gray card (or palm or coffee cup) with a reflectance meter OR an incident meter -- and use the setting in the middle of both readings. Not exactly rocket science.

xkaes said:

In Bill's example shot, it's easy to take a reading of the sunlight & shadow sections -- whether using a gray card (or palm or coffee cup) with a reflectance meter OR an incident meter -- and use the setting in the middle of both readings. Not exactly rocket science.

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Your process does not work in this case. If you're shooting color chrome film, you want to shoot based on the exposure in the bright sunny light. If you pick a middleground between light and shadow, you;ll blow out the whites in the sunny areas. With chromes you pretty much ignore the shadow areas.

On some meters, and specifically Sekonic's L758D/DR, neither meter system (reflected or incident) is gospel "18% grey", but around 12.7% (the exact specification is published in the L758D user manual which is not with me as I travel at the moment).

A grey card is used as either the first, middle or last reference in a series of readings, all then averaged. Reading off the palm of one's hand, or green foliage etc. does not work in the same way and can potentially lead to very erroneous readings.

It's hard enough to find a gray card within reasonable quality control standards, much less a standardized palm of a hand. Foliage can work quite well with sufficient experience. But one has to keep in mind that neither the meter nor film sees the reflected spectrum of all the different kinds of foliage like our eyes do.

Alan - one works with the light and illuminance range on hand. Bright sunny situations are challenging for chrome film, especially Velvia. Working in subdued light makes life easier,
especially if one intends to print their shots.

Taylor K Nankervis said:

On some meters, and specifically Sekonic's L758D/DR, neither meter system (reflected or incident) is gospel "18% grey", but around 12.7% (the exact specification is published in the L758D user manual which is not with me as I travel at the moment).

A grey card is used as either the first, middle or last reference in a series of readings, all then averaged. Reading off the palm of one's hand, or green foliage etc. does not work in the same way and can potentially lead to very erroneous readings.

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You might be thinking of the calibration constants, which are not the same thing. From the Sekonic's L758D/DR users manual.



The manual did have an interesting feature.


The

Seek and ye shall find. I absolutely avoid market-saturation products made in China, and that includes the plethora of poor to very poor quality grey cards that, in a few memorable instances years ago, bore no relationship to the established mid-tone grey value!!

Calibrite grey cards in credit card size, stored in a key-pass holder, have been my go-to choice for a long time now. They are not cheap, but undeniably very well made. Each lasts around 10+ years; the current card has been in use since 2016. Only proviso is that they, like all grey cards, be stored in a dry place, and out of direct, intense sunlight. Similarly, a Calibrite colour checker card (credit card size) is included in the first frame of each roll of film and compared against a reference spectrum at the lab.

DREW WILEY said:

Alan - one works with the light and illuminance range on hand. Bright sunny situations are challenging for chrome film, especially Velvia. Working in subdued light makes life easier,
especially if one intends to print their shots.

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It absolutely amazes me that anybody would dare expose RVP50 in bright point light. It is not designed for that, and certainly the results will look, frankly, bloody awful, even by today's RA4 or giclée printing, never mind what happened back when Ilfochrome Classic was the go-to for printing from chromes. Compare the gaudy, over-enriched colours of indiscreet RVP50 shoots in bright sunlight with photography that is more easily managed (modulated — with or without a polariser) in diffuse/hazy/overcast light. If you want to expose Fuji chrome film in bright sun, use Provia 100F, but leave RVP50/100 to the light is knows and responds best to.

Camera exposure profiling is “interesting” but I chose to set clipping points on whole stops and call it Zone System calibration. Meaning instead of fitting camera to meter, I was fitting meter to Zone System.

I left the constants at factory defaults.

baachitraka said:

The best gray card is the dome of the incident meter. But there is known trick to meter shadows or highlights.

Always works!!!

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There is no trick, no rocket science, no mystery. The lumisphere and spot meter both have their critical applied uses. Neither is superior to the other in each and every application. With a spot meter (1° in the case of the Sekonic L758D/DRs)

• Meter a bright section of the scene, but not a bright spectral.
• Meter a transitional scene between bright and dark; and
• Meter a shadowed area, but not completely black
Areas that require special consideration by the meter can be double-tapped;
• Average all.

Simple way is to use a grey card, locked in as reference reading No. 1, then all the other readings and
averaged — very quick and efficient. Spot/incident/mixed metering is critical to a good exposure (but every photographer will have his/her own preference of what constitutes a 'good exposure' in their experience), but the process of metering should not be over-complicated!