White Balance & Exposure for Dummies

[Jonathan Shaw]

I actually thought that grey was the best colour for white balance unless you want to use warm / cool cards?

Jon

[Peiter Jerzak]

Now I'm confused. I may be incorrect, but I thought Gray was for exposure readings (Amount of light) and White was for White Balance (Color Temp).

[Jeff Rhode]

Here is part of the Wikipedia def, of gray card :
"In addition to providing a means for measuring exposure, a gray card provides a reference for white balance. White balance, or color balance, refers to the setting that the camera uses to compensate for the illuminant color in the scene. Gray cards are useful for white balance since their reflectance is not as intense as that of a white object, which reduces the possibility of clipping, or exceeding the maximum possible reflectance value that the camera's sensor can record.
Gray cards can be used for in-camera white balance or post-processing white balance. Many digital cameras have a custom white balance feature. A photo of the gray card is taken and used to set white balace for a sequence of photos. For post-processing white balance, a photo of the gray card in the scene is taken, and the image processing software uses the data from the pixels in the gray card area of the photo to set the white balance point for the whole image."

As a note on using the sleeve of a white shirt, this is what is said :
"clothing washed in typical detergents contain fluorescent whitening agents, they tend to not be very spectrally neutral." However, it's better than nothing and if it works for you go for it.

[Phil Taylor]

Peiter Jerzak, your assumption is correct! Grey card for exposure, white card balance for temperature of color in the scene.

[Alan Craig]

Originally Posted by Allan Black

When you order an Expodisc for the A1, IMO get the 82mm. With step-down rings it'll cover your other lens. Check you're ordering the correct one, there are warm ones available, as I found out too late.

Cheers.

Allan Thanks for the advice but already ordered 72mm.

Alan

[Lloyd Coleman]

Gray or white can be used for white balance. The key is having something that does not have any color cast or tint. Gray cards are made to be completely neutral as are white cards that are made for white balance. The problem is that many people use anything white (sheet of paper, tee shirt, etc) that may have a color cast. You will notice that different sheets of paper can be different colors of white. This is how the warm cards work, they have a slight blue cast so the camera adds a little warm color to offset the blue cast.

[Jeff Mayne]

And if you take my advice and use the expodisc you will never have to worry about grey vs white. The filter takes the color of your light source and balances your camera to that color temp...

[Kees van Duijvenbode]

And how does that Expodisc work in practice? Do you have to screw and unscrew it every time you want to WB? If that's the case I donn't think it's very practical.

[Shiv Kumar]

Peiter,

From what research and testing I've done....

Yes a gray card is typically used to get the correct amount of exposure. In difficult light/color situations such as snow or black objects the reflective exposure meters on cameras (both still and video included) have a hard time determining the correct exposure.

So typically, your snow ends up looking gray and your black cat/dog ends up looking gray as well (or just not black). To help with such situations a gray card helps determine the correct exposure. If you take a photo of a gray card and look at the histogram you'll notice just a spike towards the middle of the scale. On Canon cameras this spike is normally 1/3 a stop under exposed. This difficulty in determining exposure using reflective meters is the same reason pros seem to use those ambient light meters rather than reflective, since different colors have differing reflectance.

Now I've tried using a gray card for white balancing purposes and compared it with a white card. I've got a card that is gray on one side and white on the other side. There is a definite difference between the two. The picture you get with the gray card seems to be somewhat warmer. At least that's the feeling I have.
The other difference comes from how one holds the white/gray card with respect to the light source and camera. If the light reflects directly into the camera things don’t quite turn out as expected. In fact I’ve had the hardest time white balancing at times. I’ve not tried the expo thingy but I’d say that ambient will work better than reflective.

On another note, when I’m outdoors and need to white balance (to be sure) I simply hit the White Balance button. I’m not pointed at anything white but the shot is a wide shot. The camera faithfully white balances.

Chris, I’ve looked at the DCS stuff many a times and even though I’m sure their stuff is great, their pricing is way too high. As a hobbyist I can’t bring myself to pay $600 for a few sheets of paper :) I wish some of their products were affordable. :)

[Jack Walker]

Originally Posted by Kees van Duijvenbode

And how does that Expodisc work in practice? Do you have to screw and unscrew it every time you want to WB? If that's the case I donn't think it's very practical.

Here's a video tutorial on using the ExpoDisc:
http://www.expoimaging.net/support/videotutorials.php
The links on the left will also take you to a faq and the instruction manual.

I have been looking at this awhile but didn't order one until yesterday. However, I am taking stills and videos in studios with bizarre colored walls and mixed lighting. It has been impossible to get a white balance that ever matches anything. I decided this would be my best bet.

From the video it appears the disc only has to be held over the lens, not actually attached (thus the suggestion to get one for the largest size lens you have, which in my case was 82mm for the Fuji lenses which will cover my 77nn DSLR lens and the Canon 72mm lens as well as smaller leneses). Then you can take a reference still in a DSLR or you can push the white balance button on a video camera. There is also a 4x4 square version I saw on the website that will go in a matte box.

By the way, if you want to try the technique (and maybe save the $100) some have written that two white coffee filters can be used in exactly the same way as the ExpoDisc.

However, even though seemingly expensive, the ExpoDisc seems to be fast, accurate, consistent and convenient--and for me this was worth the price.

With my DSLR, the Pentax K20D, I can adjust color offsets after I white balance. The ExpoDisc gives me a consistent white that I can then change an exact amount to what I may want, even in very different lighting situations. I suppose this would be similar to applying presents with the XH-A1. With the DSLR, even though I usually shoot RAW, the ExpoDisc should give me a consistent reference -- much better than trying to shoot a card in a mixed lighting situation.

[Shiv Kumar]

Oh one other thing I've notice. This applies to those of us who have a 35mm adapter (doesn't matter which one).

Each lens you use changes colors a bit so it becomes imperrative to white balance after you change lenses. Now I don't know the technical reasons behind this but I assume the glass and/or amount of glass has something to do with it.

[Brent Kolitz]

Originally Posted by Kees van Duijvenbode

And how does that Expodisc work in practice? Do you have to screw and unscrew it every time you want to WB? If that's the case I donn't think it's very practical.

Apparently you can just hold it right in front of the lens, as long as it covers all the glass.

But -- from what I see in their video, you have to move the camera to where the subject is, in order to use the Expodisc? If so, that might be OK for handheld shooting, but it seems incredibly inconvenient if your cam is on a tripod (particularly a big camera). Is this the case?

[Shiv Kumar]

Brent,

Yes this is the case. Essentially the camera has to see the light that is incident (falling) on the subject for it to be able to:
1. Act an an incident light meter
2. See the light and therefore allow for color correction.

But that is the nature of incident versus reflective meters anyway.

[Brent Kolitz]

Shiv,

Thanks for the confirmation. I can see this working into the flow alright with a D-SLR in the studio, but with a big video camera on a tripod, it's certainly a lot easier to run a balance card over to the subject, I'd have to say...

[Shiv Kumar]

Brent,

Yes, I guess different situations require different solutions. If color correction in post works great for you (meaning you've shot a card of some sort that you use as a reference in post) then you should stick with that I guess.

I've shot a few interview style videos and I guess if I really had to, I could dismount the camera from the tripod and take it over to where the subject(s) are and do a white balance. I don't know. I don't have one of these discs but the reason I've not bought one is I just didn't hear much of a buzz about it. Now I hear the buzz but the point you bring up....

I don't know, I guess its a matter is making it part of the checklist and then just doing it because :)