Cavik

Wow - this has been a challenging journey so far. I have used a point and shoot for 40 years and recently bought a Canon T6 to experience the joy of creating certain types of photos that I see others capturing but I have to say there is a big learning curve. Over the last couple months I have stalked this site collecting as much information as I could absorb and I have to say it has been a treasure chest. Between this site, YouTube and some online classes I am just now starting to feel like I am beginning to understand the basics of exposure, lens physics, camera settings, composition, etc. Believe me when I say that I know I have a LONG ways to go but it is nice to actually see some progress on my understanding of some of the basic elements. However, I now have a couple questions. First... I am currently learning about using an 18% gray card for determining correct exposure and I think I understand that this card is 50% black and 50% white mix which makes a great color for setting an exposure so that the histogram can be centered but why is it called an 18% gray if it is right in the middle between white and black? Second question is do any of you use this method of setting exposure or do you rely on the internal light meter in the camera? Is there an advantage to using a gray card? I really hope this post makes sense - like I said before... I think I am getting a handle on some concepts but being a newbie I might be way off and not know it. I pray that you will allow me a measure of grace until I can get up to speed.

User ID

Using the gray card's reading at face value will work only if
you accept whatever tones the subject matter winds up with.

Usually this is not a problem. But sometimes you look at the
playback and realize that your subject scene is not the usual
typical hodgepodge mix that the gray card simulates.

Very few photographers actually have good reason to use a
gray card as routine to their work, but if you grasp what it's
use represents, it's a fine piece of practical photo education.
You're indulging in an archaic method, and that is often the
best way to come to understand modern technologies. Like
the med students who dissect lower animals before moving
on to the human body and high tech medical practices.

When you're beyond the lesson it teaches, keep it for other
reasons. If you do your own printing, it has a different use
than simply determining camera settings for photos.

BTW, it's not covered in a pigment called "18% gray". It is
gray, and has a reflectivity of 18% compared to titanium
oxide white, which in itself does not reflect 100% of all the
light that strike it, or it would be a mirror :-)

Hope that settles the "18%" thing without gettng into a
long treatise on film/sensor response characteristics and
the nature of human visual perception ... do that later :-)


`

bsprague Loc: Lacey, WA, USA

1. A normal day in a normal world reflects 18% of the light falling on it. Therefore the card is designed to do the same.
2. I quit using a card when I stopped using film. That worked, but with digital it is so easy to bracket.
3. I see no reason or advantage to routinely using a card. It is one more complication and a thing to carry. Compare it against the palm of your hand. Is it far off?

Cavik

Thanks to both of you for your insights - they are appreciated.

photogeneralist Loc: Lopez Island Washington State

Unless you've been washing your hands in used diesel engine lube oil and regardless of your race, the palm of your hand reflects 1 stop more light than an 18% grey card. Make sure that your hand is in the same light that your scene is illuminated by, meter the palm of your hand then increase the EV setting on your camera to "overexpose" 1 stop from the meter's indicated setting. This is an oldtimer's trick. You didn't have to carry a greycard because most of us will have a palm with us at all times. But that's now useless information in the digital world with instant view screen display and histograms and overexposure blinkys in the viewfinder.

photogeneralist Loc: Lopez Island Washington State

Duplicate file, please delete, Thanks

Shutterbug57

Use the flip side to set a custom white balance (assuming that the flip side is white).

Gene51 Loc: Yonkers, NY, now in LSD (LowerSlowerDelaware)

This may help you to understand what a grey card is used for and how it is not exactly accurate.

https://marcschlueter.wordpress.com/2011/08/06/light-meters-grey-cards-and-the-ultimate-answer-its-12-not-18-and-42-is-totally-off/

But, to answer your second question, if you use a grey card, you can use the camera's metering, as long as you set it to spot meter mode, do not include anything else in the area that the meter is reading, and you can conveniently place the card in exactly the same light as your subject. As you can see, it may not always be convenient. Such an approach will not work if you are in a blind shooting wildlife, at a sports venue where you are sitting in shade while the players are on a sunlit field, a stage performance, etc etc etc.

With digital, the paramount concern is overexposing highlights. If you make that mistake, absolutely nothing will be recorded in those areas. So the goal is to expose the scene as brightly as possible without crossing that threshold. One successful approach is to simply measure the highlights where you want to retain detail, and add 1-1/3 to 2 stops additional exposure to the reading. The reason I qualify this with "want to retain detail" is that there are some situations where blown highlights are ok - night shots were streetlights car headlights and other features will be bright and without detail, or subjects with strong backlight, where the backlight will create a bright "halo" and that halo will be blown, or a seascape where the water is throwing very bright specular highlights.

Part of the skill in setting exposure in this manner is being able to evaluate the scene, and the reflectance of elements in the scene.

A google search of "zone system for photography" will yield a trove of helpful information.

Using a grey card is perfectly valid - even in scenes of great contrast. If you consider an image of three cats - a white one, a black one and a grey one - using a grey card would be like reading the grey cat and setting your exposure. The black cat is reflecting less light, so if you were to base your exposure on the black cat and use the reading without adjustment, the black cat would turn out grey, the grey cat would be very bright, and the white cat would be an unrecognizable white blob - and the opposite would happen if you set your exposure based on a reading of the white cat.

When you can place a grey card in the scene, and measure it's reflectance to set your camera, it is a perfectly valid, accurate means of establishing a good exposure. It will work 99% of the time - but only in those specific circumstances.

Silverman Loc: Michigan

I have never used a "Gray Card", and not sure I will ever use one.
Although, I did pick up a method of setting up my exposure in Manual mode, which was reffered to as the; "I Am Shooting" method.
1st set ISO
2nd set Aperture
3rd set Shutter Speed
When done your Camera meter should be set at "0".
I found this on U-Tube video from another professional Photographer.

rmalarz Loc: Tempe, Arizona

These might help a bit on the basics.
Exposure Series

Exposure and How It Works - A Beginner's Guide
http://www.uglyhedgehog.com/t-484554-1.html

More Exposure and How It Works - A Beginner's Guide
http://www.uglyhedgehog.com/t-484826-1.html

Finishing Up Exposure and How It Works - A Beginner's Guide
http://www.uglyhedgehog.com/t-485845-1.html
--Bob

NormanTheGr8 Loc: Racine, Wisconsin

In the field I use the white patch of fur on my dog usually works well

MikeT9

Excuse my possible ignorance regarding all those people going on about exposure and using a grey card. A grey card, which as someone says reflects 18% of light, is not used to calculate exposure but to correct inaccurate white balance which will alter the colours in the picture you are taking. If you are shooting in raw you can change the white balance to suit, the exposure has nothing to do with it. You can meter off your palm as much as you like to get the exposure correct but if, for example, you’ve got your camera white balance incorrectly set the colours will be incorrect. If you are shooting birds, using a grey card and taking a picture in the same light as the bird will enable you in post processing to get the correct colours in the bird.

rmalarz Loc: Tempe, Arizona

A gray card can be used to determine exposure. A good quality card will indicate Zone V which an exposure meter is reading for. However, the dynamic range of the scene may influence the outcome of using that exposure.
--Bob

JohnSwanda Loc: San Francisco

A grey card can be used for either exposure or custom white balance. They have been used for exposure before digital came along and WB became an issue. When you use a grey card for exposure (or the palm of your hand) you are measuring light falling on the subject rather than reflected off it, which can give more accurate exposure.

scubadoc Loc: Sarasota, FL

I have used an 18% grey card in the field in the following way: if I am doing a series of shots with the same lighting, I may include the card in the first shot. If I am shooting Raw with AWB, when I post process, I will set the color balance by placing the color picker on the card, which will usually give me the correct color balance for that entire series. Then just sync the series to that first image. It helps in tricky lighting situations.