[argyllcms] Re: Some ambient measurements with the i1D3
- From: Stephen T <stwebvanuatu@xxxxxxxxxxxx>
- To: "argyllcms@xxxxxxxxxxxxx" <argyllcms@xxxxxxxxxxxxx>
- Date: Sat, 28 Jul 2012 18:15:34 -0700 (PDT)
I was referring to the colorimeter and not camera white balance.
The i1D3 did not measure as expected when pointed directly at the sun. I had
some bubble wrap close at hand and used that to attenuate the brightness of the
sun. The i1D3 then gave me 5000 K although the 6500 K test was off the daylight
locus. Maybe not a great idea.
ST.
________________________________
From: Ben Goren <ben@xxxxxxxxxxxxxxxx>
To: "argyllcms@xxxxxxxxxxxxx" <argyllcms@xxxxxxxxxxxxx>
Sent: Sunday, 29 July 2012 12:14 AM
Subject: [argyllcms] Re: Some ambient measurements with the i1D3
On Jul 27, 2012, at 11:48 PM, Stephen T <stwebvanuatu@xxxxxxxxxxxx> wrote:
I put four layers of clear bubble wrap over the diffuser to get sensible
readings.
>
I would be quite wary of the color cast the plastic might be imparting. Much
better -- much, much better -- would be a styrofoam coffee cup. Polystyrene has
as flat a spectrum as you're going to encounter in the real world, and the
thickness of most cups is such that they transmit just about much light as a
gray card reflects.
Indeed, if you have any expensive photographic white balance targets, I'd
suggest putting them all away and using a styrofoam cup instead. It's more
neutral, plus it lets you either simultaneously sample the light of different
parts of the scene (put it in the middle of the scene, and the curved sides
give you a nice gradient from each source to the next) or of the average of the
entire scene (put the cup over the lens).
Another excellent cheap alternative is Tyvek. It also has a flat spectrum, but
Tyvek is 98% reflective, whereas polystyrene is about 80% reflective. The
coffee cup is great for general-purpose photography because that's about the
reflectivity you want for in-scene white balance, because it's curved, because
it's cheap, and because you can find one anywhere. The Tyvek is good for copy
work or other instances where you want a flat white balance sample. It's also
cheap; you can get a whole pack of Tyvek envelopes at your local office supply
store for just a few dollars. Canon sells large format printer banner roll
media made of Tyvek; the front is coated with their Heavyweight Matte coating,
but the back is pure uncoated Tyvek (but only the front is printable). If
you've got a ColorChecker Passport, cut out a piece of Tyvek and place it over
the white balance target on the inside back cover.
Cheers,
b&
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