"77mm Pringle filter" :biggrin: The earlier Pringles' lids used to be made out of a semi-transparent white plastic and were exactly 77mm, the size of most of my lenses. Someone did tests of the Pringle lids vs Expodiscs and a lot of folks said that the Pringles lid had truer white balance.
I love it, use it all the time.
Which one is the Expodisc and which one is the Pringles???? click image for original sized version
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I've also used these with great success http://www.qpcard.se/BizPart.aspx?tabId=84&tci=137
They come in a foil pouch and are basically the same principle except they also give you a white point and black point in your initial photo as well, you can just make a simple curve and apply it to the rest of your series.
I have the pocket card as well and am happy with it. It's strange that it wouldn't give me correct white balance in the studio environment though. Ended up getting a standard gray card from the local print shop for $5 and that seems to work better for studio lights.
I use it. It has become an indispensable part of my kit. I have even clipped one to each of my cameras to make sure they go with me. Since I use Raw WB is no longer an issue..one thing less to think about.
Card works very well when you can get it into same light as the scene your photographing; not always possible, like from a boat or some distant landscapes. Being an engineer, I have artisitic issue as its use will balance the scene to neutral gray even if it's illuminated by a reddish rising or setting sun.