White balance question

[Grevolorio]

Hi everyone,
This is my first post to this forum even though I've been following it for a while. I've tried IR fotography with my Canon 10D and a 50mm 1.8 lens but I have problems with the focus, I can seem to focus properly regardless of what I do. I have an Oly C750UZ which I haven't tried for IR before, it's the next one to go. However, I got back my first digital camera, a Nikon Coolpix 775 that I had already shelved and it is great for IR, the thing I like the best is that I can actually see the image before pressing the shutter and I don't have to use LOOONNNGGGG shutter speeds as with my 10D.
Now, to my question: In your tutorial, you advise to get a white balance reading of a grass patch or the blue sky. Can I use a gray card instead?

TIA and keep the good work!!!
Respectfully, Gus

 

[teerex]

Hi Gus,

I guess you can use the gray card for CWB, but then post processed results would differ from the usual you see posted.

Reason why a patch of green grass is used for CWB is that the camera records that as "white". So with post processing all green (same tone as that used for CWB) will become white. That constitutes to the while leaves and foliage in IR post processed pictures.

Depending on the percentage of gray card you're using to set CWB. When shot, all gray tones captured will be post processed as white, thus giving different results.

As in normal colour photography, some people use a 18% gray card for CWB. This would give them a very slight off tone white in the colour photos.

These are as per my understanding of setting CWB.

Anyone would like to comment/correct me on my understanding.

 

[PandaOng]

From my understanding, the gray card is used to check for correct exposure. Mean to say you place your gray card on the subject, meter it and it will give you a accurate exposure.

The WB is more to adjust the overall color of your picture. Just like adding a 82 or 81 filter to correct the color.

I guess you are right regarding the balancing of color of foliage in order to get a 'white' green.