March 29, 2011

How to use a Grey Card

Getting back to the origins of why I started this blog, here is a photography lesson

The importance of metering and how to use a grey card.

One of the keys to great photography is understanding exposure and knowing how to create a properly exposed photo.

The first thing we need to understand is that our cameras have built-in light meters, more to the point, they have 'reflected light' meters.  They measure the light that is bouncing off of the scene and then give us the exposure settings (shutter speed, aperture & ISO).  

The problem with this, is that the things we photograph will reflect different amounts light, which we see as different tones and colors.  The camera doesn't know what it's looking at, it just knows how much light is reflecting off of it.   

For this system to work, the cameras have to be programmed for a certain amount of light...we call this middle grey.  The camera assumes that the average reflectance of the scene will be the same tone as middle grey, so it gives you exposure settings that would work if your scene was actually middle grey.   Fortunately, this is often the case, which is why many of the photos you take, don't look too bad.  

However, when our scene (or the part that we meter on) isn't middle grey, we end up with under-exposed or over-exposed photos.  This is because the camera is still assuming that our scene is middle gray, so the exposure settings it recommends are likely going to be wrong.

In the example above, the scene is mostly bright white snow, which is a lot brighter than middle grey.  The camera doesn't know that it's seeing snow, just that it's bright.  Therefore, it recommended settings that caused the photo to be underexposed.  This is what you would get in any of the 'auto' modes on your camera.  I got this in Manual mode by adjusting the settings (shutter speed, aperture & ISO) until the 'needle' on the camera's meter/scale got to zero (...0...).

One of the best tools to ensure that you do get properly exposed photos, is a grey card.  They can be found in most photography shops for about $20.  The are specially made to reflect exactly middle grey....which is what the camera is expecting to meter off of.  

To use a grey card, you place the card under the same lighting conditions that you are shooting in (that your subject is in).  If your subject can hold the card, that's great.  You then meter off of the card.  To do this, you basically fill the frame with the grey card and see what exposure settings you camera is recommending.  

Now you need to lock your exposure at that exposure value.  With an SLR type camera, you can use Manual mode and adjust the settings (shutter speed, aperture & ISO), or you can engage exposure lock (check your user manual).  With a point & shoot type camera, you should be able to lock the exposure as well.  If you are using exposure lock, be sure not to accidentally re-meter the scene once you back up again.  That's why it's so much easier to just use manual mode.  
The exact combination of settings that you choose, will depend on your artistic goal, which is another lesson.

So now that you have locked in the settings that you got from metering on the grey card, back up and compose the shot how you like and take your photo.  

Do you see that my subject is now properly exposed?  Also notice how the snow actually looks white in the photo, like it does in 'real life'.  In this case, some of the snow is even blown out, which is because it's just that much brighter than proper exposure for my subject.  Given the choice between an underexposed photo or a bit of blown out snow, I'll choose the one that gives me a properly exposed subject.  

With my camera in manual mode, I now have proper exposure locked in.  So I can continue to shoot without having to re-meter for each shot.  Provided, of course, that the lighting conditions don't change.

So there you have it.  How to get proper exposure using a Grey Card.  This will work in any lighting situation, just keep in mind that if you change your lighting (shooting in another direction or moving to the shade etc), that you will have to re-meter to get new exposure settings. 


nikongirl616 said...

Thank you so much for this post.

Paul Garafola said...

In this example above, wouldn't the spot meter setting accomplish the same result? If not, then why? Thanks!

Rebecca said...

Very good information. Thanks for sharing.

Adirondackflytyer said... answer your question.."YES". Spot metering would work. But your camera will "meter" every progressive shot. Shooting in manual mode using a gray card will allow you many shots without "re-metering".

CasualCLICKS said...

Do you recommend saving the setting in "custom white balance'?

Unknown said...

Exposure from a young age to the realities of the world is a super-big thing. See the link below for more info.


Curtiscomeau said...

Fantastic post !
Your provided information is valuable for us.
Thanks for sharing.
Edmonton Professional Photographer