If they are different, the result will be different.
Not colourwise, but exposure wise.

I never use a grey card. I use auto WB, and when sometimes wb is wrong, I correct it in photoshop.

Are you using the gray card for white balance or for exposure readings? For white balance it likely won't matter. For exposure readings it will make a big difference.

In my estimation the gray card for 18% gray exposure readings is a little darker than medium gray. In Photoshop or other photo editor the RGB colors are 127,127,127. If your PC screen is calibrated you should be able to match the card and the screen.

Here we are:

All these years of buying and using Grey cards for white balance, and it's for exposure readings? Sorry but I must disagree.

I believe that people are saying that it's not only for white balance. When filming, I use my collapsible 18% grey card to set both white balance and exposure. Of course, I may need to fine-tune the exposure, but it gives me a very close starting point.

All of the data in your histogram should be bunched right up in the middle with 18% grey filling the frame completely.

All these years of buying and using Grey cards for white balance, and it's for exposure readings? Sorry but I must disagree.

The 18% gray card has been used decades before the invention of digital photography and the idea of white balance.
It has been invented to measure exposure.
After if you can use it for white balance too it is another story�

____

There's no way to correct mixed light temperature.

In digital photography it is not easy but not impossible, shooting different images with different WB and assembling them then in Photoshop.

With film photos it was another story.
Here for example I have done 10 or 11 different expositions (on the same sheet film) with different combinations of filters to correct lights with different color temperatures


(Sorry for the quality, it is an old XX century photo and the scan is not so good)

I dont understand how you would use it to set exposure can someone explain that also?

With a true 18% gray card you hold the card in the same plane as your subject and with the same light source. For a portrait hold vertical in front of the face with the card flat gray side oriented towards the camera normal shooting position. For a landscape maybe top tilted back a bit and standing in the same sun. With the camera close to the gray card, view only the card - don't cast your shadow on the card. Set your camera for manual control and exposure to 0ev for a non-strobe scene. With a DSLR in a strobe/studio scene, you can take a picture of just the gray card, as situated, and there should be a narrow spike in the histogram at dead center of the histogram representing the middle (18%) gray of the card. In manual mode again, adjust shutter, aperture, ISO to get the spike in the dead center. For studio strobes your shutter likely has to be 1/200 or slower for proper sync. If the gray card is not really 18% between black and white then all bets are off for correct exposure. The correct gray level on the card is required for this to work.

In my few studio occasions I do the gray card and histogram reading since I don't own a light meter that can capture studio strobes blinking. With the studio lights I also do the gray card for white balance since I'm a bit color blind to skin tones. With these two presets I can trust my output that otherwise I would personally have problems adjusting later with confidence.

Note that some very old 18% Gray cards were only made for exposure and may not be truly gray. A color cast will result if these are used for white balance. I'd think newer cards are OK.

When doing the real subject shooting, take an image with the gray card in it. The later you can also adjust that image to be the correct gray and then use those adjustments on the imagess without the card visible. This is my "fail-safe" backup for my color blindness problems. In Photoshop, adjust gray by numbers. If I got more serious I would invest in the color swatch panels and color adjust software to do this task.

A few references:
http://digital-photography-school.com/get-your-white-balance-right-in-seconds-using-grey-card
http://lifehacker.com/5659324/use-an-18-gray-card-for-better-color-balance-in-your-photos
http://www.lastoliteschoolofphotography.com/using-calibration-greycards
http://www.bhphotovideo.com/c/product/740518-REG/Datacolor_DC_SCK100_SpyderCheckr_Color_Calibration_Tool.html

Funny, I usually start with black first, a tire or grill or inside a wheel well. But as usual, it's kind of specific to what I like to shoot. 

Quote from: pixel8 on February 16, 2014, 01:14

Yes I am using it for the White Balance, I was told that no matter if its a light color grey or dark color grey its still a 18% grey and that it does not matter if its light or dark grey. I bought it from a local camera store but I was not sure if they guy knew what he was talking about so I thought I would check here.

I dont understand how you would use it to set exposure can someone explain that also?

There is black and white and grey in a picture.
It is sometimes scewed. But if it is not, you have a good oppertunity if you can set the WB on grey via photoshops levels.
Easy enough.. You have a photo. Look around and see if you can set the white, the grey or the black point.
I usually go for the white.

Yes it is a nice photo and besides good lighting it does have an attractive color balance.

Tharts a good photo, but maybe it would have been even better with mixed white balances?

There is black and white and grey in a picture.

Correction: there is black, white and grey in 'some' pictures, by no means all - many nature photos (for example) have none of these present.

NB: When reviewing images it's virtually impossible to remember if 'something grey' in a photo was 'warm' or 'cool', so setting your colour balance by a 'random something grey' in a photo can result in the rest of the photo going way off-kilter. It's really unlikely that any random grey object will be 127, 127, 127 or any other balance of RGB tones.

Funny, I usually start with black first, a tire or grill or inside a wheel well. But as usual, it's kind of specific to what I like to shoot. 

Quote from: JPSDK on February 16, 2014, 07:51

Quote from: pixel8 on February 16, 2014, 01:14

Yes I am using it for the White Balance, I was told that no matter if its a light color grey or dark color grey its still a 18% grey and that it does not matter if its light or dark grey. I bought it from a local camera store but I was not sure if they guy knew what he was talking about so I thought I would check here.

I dont understand how you would use it to set exposure can someone explain that also?

There is black and white and grey in a picture.
It is sometimes scewed. But if it is not, you have a good oppertunity if you can set the WB on grey via photoshops levels.
Easy enough.. You have a photo. Look around and see if you can set the white, the grey or the black point.
I usually go for the white.

Yes it is a nice photo and besides good lighting it does have an attractive color balance.

Quote from: JPSDK on February 16, 2014, 07:33

Tharts a good photo, but maybe it would have been even better with mixed white balances?

I'd bet in the old days you used an incident light meter and it had a crank on the side for winding it up. That's old.

We didn't use color balance with film because the film had it built in. You got what you bought, and same for ISO.

I'd bet in the old days you used an incident light meter and it had a crank on the side for winding it up. That's old.

Using an incident light meter is more or less like using a light meter with a built in grey card. Or maybe that's what you're saying.

My dad taught me to meter off the grass, normally.

I contemplated having my study painted 18% grey. I like it.

We didn't use color balance with film because the film had it built in. You got what you bought, and same for ISO.

But you would often still have to gel the lights if they were different temperatures.

With sheet film (4x5 & 8x10) in studio we would buy a case of film, shoot tests, run them through the lab and fine tune the color balance with wratten gel filters behind the lens. Depending how reliable the lab was you would be good for that case. Sometimes their chemistry would be off a bit and you would have adjust the filters to retain the same balance.
And every lab had their own color balance so it was best to stick with one pro lab and develop a good relationship with them.

We would do the same for roll film 120 mostly but you could do it with 35mm too, though usually the filters went in front of the lens on those cameras.
You could also do snip tests on a roll of film and adjust the development for either push or pull exposure.

All these would affect color balance.

PhotoBomb you didn't send it off to Sundance or Cook photo in IA? I mean back then we had those little yellow Fotomat booths all over the place? 

And since it was the "good old days" I'll explain for some of the younger members. If you took your film to the corner store, someone from one of these commercial processing places would come around every afternoon and pick up.

Some would go by truck and Cook was Mid-West would fly the film to Iowa. Depending on the process, and what they were running, you could get next day service or a few days. Eventually, B&W would take longer than color, because they didn't run it as often.

This pretty much ended with 1 Hour Photo in store processing. (Wolf, Black, Fox, whatever else, there were hundreds of them) But some of those places would bag the slides or two day stuff, and run what they needed at home.

If you wanted to know that you had fresh chemicals and good consistent quality control, you would take your film downtown or someplace that did professional processing. Something else that less and less important in the digital age with most places running computer controlled Fuji or Kodak machines now.

Definitely less problems and chance of losing everything, after you wait days to see the negatives. Now we can look at the image, exposure, highlights, and histogram, on the back of the camera. Nice!

So no, I do not long for the "bad old days". 

No I had to drive it up to A&I in Hollywood from Orange County. That sucked.