Author Topic: Gray card and my new A55  (Read 3537 times)

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Offline 18series

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Gray card and my new A55
« on: October 08, 2011, 05:49:08 PM »
Okay, I quite new to this so don't stone me when you read this.  I tried to take a picture of a friends jewelry against a white background.  The white came out looking dingy or off white.  I've been reading that I need to use a gray card to offset this.  Is there anywhere I can go to get the sequence of steps to complete this?

Offline OldClicker

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Re: Gray card and my new A55
« Reply #1 on: October 08, 2011, 09:46:27 PM »
A gray card is used to set the white balance or color temperature if it is too yellow or blue.  Non-white whites means that it is under exposed. - Terry

Offline FarmerDave

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Re: Gray card and my new A55
« Reply #2 on: October 08, 2011, 10:26:06 PM »
I think for exposure all you have to do is once you got your lighting set up, put up a 18% gray card next to your main subject facing the same direction to the camera. AE lock on the card and recompose.
I came across this item at B&H and found it quite ingenious.

http://www.bhphotovideo.com/c/product/547261-REG/Pearstone_MFCC77G_Microfiber_Cleaning_Cloth.html

18% gray, cleaning and the other side has grippy dots.
« Last Edit: October 08, 2011, 11:00:11 PM by FarmerDave »

Offline Stef.

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Re: Gray card and my new A55
« Reply #3 on: October 08, 2011, 10:40:06 PM »
First of all...nobody stones here- we are all very nice people ;)

Grey card: two ways of using it:

1. Shoot in raw. Include in your first shot a 18% grey card (you can get these from any photographic shop and they are very cheap). The best way is to put it exactly where you will put the jewelry. Do not change the light after you have done this! Keep on shooting you object with the same light. Once done open up the image with the grey card plus if you want all the other images at the same time in your raw converter. Make sure "select all" is ticked. Take the wb tool and click on the grey card. This will adjust your wb.

2. Set a custom wb. Hereby set the camera to spot metering. Turn on all the lights. Go into your wb balance setting of your camera and turn the wheel until you reach "setting custom wb". Aim the camera at the grey card and take a picture. You will not actually take a picture but the camera sets a custom wb. You need to save this custom wb to a register. (The camera will ask you) Turn your wb to that registered wb and start shooting. Now do not change any lights! Also make sure that you change your metering back to something else than spot metering! The beauty of solution two is that it works with Jpegs as well. If you go with solution 1 then jpegs are not recommended.

Hope this helps?
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Offline chappo1

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Re: Gray card and my new A55
« Reply #4 on: October 08, 2011, 11:21:10 PM »
Okay, I quite new to this so don't stone me when you read this.  I tried to take a picture of a friends jewelry against a white background.  The white came out looking dingy or off white.  I've been reading that I need to use a gray card to offset this.  Is there anywhere I can go to get the sequence of steps to complete this?

I may be the one getting stoned but I think from, what I perceive you to be asking, that the "gray card" might need some explanation.
Our eyes adapt exponentially but a camera meter is linear and the makers have to set a reference point so they choose a mid gray.  Now the light meter in the camera assumes that what you are metering off is this gray.  It tuns white into gray and black into gray.  If you are shooting in the snow or at a white sand beach (or using a white background) you need to over-expose by 1 to two stops to get the perceived gray to be white.  (for black you underexpose in the same way). 
If you want to do a trial, set up your white background, your gray card and a black object and spot meter on each of them in shutter priority.  You will see the camera change the aperture by the one to two stops......john

“Time is a great teacher, but unfortunately it kills all its pupils."

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Offline 18series

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Re: Gray card and my new A55
« Reply #5 on: October 09, 2011, 12:23:57 PM »
Thanks  for all the input guys, I went out and purchased a gray card yesterday and will let you know it works or doesn't work out for me later on today.

Offline shamb

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Re: Gray card and my new A55
« Reply #6 on: October 11, 2011, 05:49:23 PM »
Probably too late for the OP, but if you have an old cereal box (cornflakes, etc) the inside grey cardboard makes a very good grey card (as long as it is not the waxed kind).

I did a few tests between a real grey card and the inside of a cornflakes packet, and there is no discernible difference in setting the white point for me. Also worth noting that a real grey card is set for 18% reflectivity, but as digital cameras don't actually use the 18% value (they tend to use a brighter value), its not actually critical anymore.