Issue with auto-focusing on gray card

Hello,

I recently bought Scott Kelby's PS4 book that came with a gray card so I decided to use it to set up custom white balance in camera.
My camera would not auto focus on the card when I zoomed in (with 55-250) to only have the card in frame. I switched to MF and was able to get it done but auto focus just would not lock in.

I am shooting RAW now so its not such a big deal as I can use that gray card to set WB as long as its in the frame (I hope I have that right) but just wanted to make sure my camera or lens is not "broken".
It very well could be me too, but thats another story.

You need contrast in order to focus.. There is no contrast on a gray card, so the camera can't focus. You have to put the lens in MF mode. This is normal.

A) You'll have poor luck getting AF on any single toned item (gray card, white wall, etc) due to the way that the AF system works. This is perfectly normal.

B) Focus is unnecessary for setting your white balance that way. Just make sure your exposure is correct and take the shot. I'll frequently shift the shot OOF for white balance just to have an even tone across the sample shot <shrug>

You will have to use MF as the AF needs a difference in contrast to work (black lines on a white background etc.) - put the card on a dark background and focus on the edge of the card and it will work for instance.

Thank you all for the info.
Now that I read your responses I remember reading something about the AF looking for contrast.
glad to hear my eqipment is working OK.

And you don't need to focus at all anyway, just to set white balance.

amfoto1 wrote in post #12780405
And you don't need to focus at all anyway, just to set white balance.

Bingo.

....it won't focus on a blue sky either......saved ya another thread....lol

Why don't you focus on the edge of the card, then move the camera a little into the center to meter?

Get a better grey card ..... Whibal. http://mtapesdesign.co​m/whibal/

Has a focusing centre.

James

I wouldnt get to crazy with custom WB. Setting a custom WB for every shoot is a pain in the rear. If your shooting people just have your model hold the card the first shot, then toss it to the side and then use a dropper tool to apply it to all the images.
If its a stationary objects you can do the same. There are plenty of playing card sized plastic cards you can throw in your pocket. Lastolite has a great large foldable. I use Forensic photo rulers.

Higgs Boson wrote in post #12780626
Why don't you focus on the edge of the card, then move the camera a little into the center to meter?

I will, now that I know what and how to do it.

Old Mechanic, I knew how it works with shooting people but was just wondering why camera wasnt auto focusing on it. thats how the thread came about.

all the responses here were very helpful, thank you kindly.

OldMechanic wrote in post #12780746
I wouldnt get to crazy with custom WB. Setting a custom WB for every shoot is a pain in the rear. If your shooting people just have your model hold the card the first shot, then toss it to the side and then use a dropper tool to apply it to all the images.
If its a stationary objects you can do the same. There are plenty of playing card sized plastic cards you can throw in your pocket. Lastolite has a great large foldable. I use Forensic photo rulers.

Great advice. I would be interesting to see how much it differed via setting the custom WB in camera & PP'ing it via the grey card shot.

SeanH wrote in post #12781218
Great advice. I would be interesting to see how much it differed via setting the custom WB in camera & PP'ing it via the grey card shot.

If you look in the camera manual at the instructions for setting a Custom WB (you can check the index for that term) then when it tells you to photograph the white "target" it would specify setting the lens to MF!

tonylong wrote in post #12781243
If you look in the camera manual at the instructions for setting a Custom WB (you can check the index for that term) then when it tells you to photograph the white "target" it would specify setting the lens to MF!

Thanks, but that wasn't what I was talking about. I've used a in camera custom WB many times shooting in stadiums.

SeanH wrote in post #12781320
Thanks, but that wasn't what I was talking about. I've used a in camera custom WB many times shooting in stadiums.

That's fine, I was just having fun reminding people to "Read The..Manual"!