DIY gray card?

[DREW WILEY]

How do you know "white" paper is really white"? How do you read the oblique reflectance level of that paper (yes, that counts too), or of the so-called black ink, which infamously vary in sheen with inkjet unless one is highly selective. One can't even find a "white" paint with a reflectance above 90%, unless it's a special technical products very few people know about (pure barium oxide reaches around 98%, with a commensurate high cost). All of this is just "shoot from the hip" guesswork. I'm all for having fun trying, but if someone wants something reliable, just spend sufficient money for the real deal up front.

 

[Donald Qualls]

just spend sufficient money for the real deal up front.

Your solution for everything. Of course, what, $50 for a small MacBeth plate, then $120 to get it overnight, as in the OP needing it "tomorrow" (which is now a week or more ago).

 

[KenS]

Hi
Is there a way to do a 18% gray card in the darkroom? I need a 8x10 gray card quickly and I thought it could be made with the enlarger and then checked with the light meter of a digital camera.
Has anyone done something like that?

 

[alanrockwood]

One important fact (I think it's a fact) is that 18% is not actually the correct reflectance for photographic purposes. I believe that most meters are calibrated to something closer to 12.5% reflectance. The value of 18% is more or less a result historical accident, coming originally from ink press printers, not from photography.

The difference between 18% and 12.5% probably doesn't make much different for conventional black and white negative films, but it could make a difference for materials that have less exposure latitude.

I could be wrong, and if so I am willing to stand corrected.

 

[David Lyga]

Rafael:

You know, this might even be better. What if you took a sheet of pure white paper, either fixed darkroom paper (NON glossy is best) or simply a sheet of copy paper. Then ... all you would have to know is 'how many stops to adjust your reading'. This would probably be about three or four, but you could do the experimentation. That way, you would rarely have light that is too low for a reading and could simply mentally adjust your readings. - David Lyga

 

[Donald Qualls]

To get from 90% to 18% (5x less light) is 2 1/3 stops. Same as from ISO 100 to ISO 500.

 

[RalphLambrecht]

How do you know "white" paper is really white"? How do you read the oblique reflectance level of that paper (yes, that counts too), or of the so-called black ink, which infamously vary in sheen with inkjet unless one is highly selective. One can't even find a "white" paint with a reflectance above 90%, unless it's a special technical products very few people know about (pure barium oxide reaches around 98%, with a commensurate high cost). All of this is just "shoot from the hip" guesswork. I'm all for having fun trying, but if someone wants something reliable, just spend sufficient money for the real deal up front.

still, a reliable DIY gray card is easily made by trial and error with the help of a reflection densitometer.

 

[AgX]

still, a reliable DIY gray card is easily made by trial and error with the help of a reflection densitometer.

As I indicated above in post #4, a lightmeter yielding both incident and reflective metering would do so too. Such device is more spread amongst us than a densitometer.

Care only must be taken at the small-object metering that one does not shield the gray-card oneself, but that would be the same in actual use...

 

[bernard_L]

I have recently tried a homemade 18% card. It is a 500x400 grid of cells with a random 82% of them filled black. I print it with an injet printer on some random white paper. It comes out looking darker than I think it should (but not by all that much). I think the problem may be the black ink soaking out into the clear spaces. It might work better with a laser printer, but I don't have access to one.
I would upload it here, but it seems to not be permitted due to it being a 6mb pdf.
B.

Sounds like a better idea than printing "gray" with a color inkjet printer.
The bad: Whiteners in the paper make it blue(ish) when exposed to solar light. How do I know? Made myself a DIY gray card and used it on a distant trip, for color negative pictures. Felt clever. Used one shot of the card per roll to set neutral gray. But colors were just not right. Months later, visiting an art show with UV light, had a glimpse of a piece of "white" paper, and... aha!.

 

[AgX]

Optical brighteners you basically may find in halide papers too. But also in the photographic subject ...

 

[RalphLambrecht]

Sounds like a better idea than printing "gray" with a color inkjet printer.
The bad: Whiteners in the paper make it blue(ish) when exposed to solar light. How do I know? Made myself a DIY gray card and used it on a distant trip, for color negative pictures. Felt clever. Used one shot of the card per roll to set neutral gray. But colors were just not right. Months later, visiting an art show with UV light, had a glimpse of a piece of "white" paper, and... aha!.

The problem with the laser printer is that they are black it's too much of a dark gray and really not black at all.

 

[Mr Bill]

Sounds like a better idea than printing "gray" with a color inkjet printer.
The bad: Whiteners in the paper make it blue(ish) when exposed to solar light. How do I know? Made myself a DIY gray card and used it on a distant trip, for color negative pictures. Felt clever. Used one shot of the card per roll to set neutral gray. But colors were just not right. Months later, visiting an art show with UV light, had a glimpse of a piece of "white" paper, and... aha!.

This is exactly why, in post #26 here, I suggest using the museum-grade white mounting board. This is a pretty reliable way to get something without fluorescent brighteners in it.

Fwiw that bluish tinge in "white" things has been an issue for wedding photographers since at least the 1970s. I tell people to always make sure to only use flash units with "UV coated" flash tubes. (These mostly filter out the UV component that sets off the brighteners.) It's mainly the cheaper units that don't filter out UV, so the photographer ends up with a bluish tinge in white wedding gowns (white clothing almost invariably contains brighteners). A flash that filters out UV won't cause this issue. Of course, outdoor light WILL still fluoresce a wedding gown, but at like one can control it in indoor photos under flash.

 

[DREW WILEY]

Ralph - a reflection densitometer reads at a specific direct angle. But gray cards get employed at varying angles of incidence relative to illuminant and meter. That's just one reason why the degree of sheen of the specific ink blend could cause mistaken readings. It's really no different than commercial plastic gray cards on shiny plastic - they can be deceptive too. Sheen is a significant issue, and it can even be affected by the RH at which inks dry. Ideally, you'd want to choose a relatively matte ink to avoid this kind of issue. You probably know that anyway; but I'm stating this for sake of the general readership.

 

[AgX]

It's really no different than commercial plastic gray cards on shiny plastic.

This should not be read as all commercial cards being shiny.

 

[DREW WILEY]

Yep. Another thing to consider if buying a commercially made card. Modern gray discs on fabric are more consistent in that respect, even though the quality control per percent of gray can vary brand to brand. I've had good luck with Impact QuickBalance discs - a bit pricier than many others, but well worth it.

 

[wiltw]

I once thought that since 18% tonaity is the 'midpoint' of the tonal range, if I created a checkerboard pattern of alternating black squares and white squares, an averaging meter would average 0% density and 100% density to the midpoint...nowhere close!

 

[bernard_L]

I once thought that since 18% tonaity is the 'midpoint' of the tonal range, if I created a checkerboard pattern of alternating black squares and white squares, an averaging meter would average 0% density and 100% density to the midpoint...nowhere close!

a) This 'midpoint' of the tonal range stuff is just internet folklore. The 18% is supposed to approximate the average reflectance of a typical real-life scene (some argue 12%, pls don't start that here). And, in said typical scene, deep shadows are Z0, while sunlit paper is ZVIII; so the mid-point, if you are serious about that argument, would be ZIV...
b) A checkerboard pattern of alternating black squares and white squares has an average reflectance of 50%; or reflection density 0.3.That is how it would appear to a meter, provided it is actually averaged, either because the FOV of a reflection reading encompasses many squares, or because (TTL) the checkerboard is fine-pitch and thrown out of focus. Simulating continuous tone with a pattern of just lack and white is the principle of halftone screens used in printing newspapers and magazines.

 

[Individual One]

a) Simulating continuous tone with a pattern of just lack and white is the principle of halftone screens used in printing newspapers and magazines.

That is where I am coming from with this idea. I used to work at a graphic arts company, which is now part of Kodak (maybe one of the only profitable divisions, but let's not stir up the haters). We had AM screens which varied the dot size on a uniform pattern to produce grey scale, or the better practice of FM screens which varied the frequency of a random dot pattern and thus did not produce the familiar screen beating artifacts that can be seen so often.