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Re: [OM] Spotmeters

Subject: Re: [OM] Spotmeters
From: Chuck Norcutt <chucknorcutt@xxxxxxxxxxxxxxxx>
Date: Mon, 23 Feb 2015 13:04:09 -0500
I don't consider a filtered image to be a raw file... at least not as the manufacturer intended it to be.

Chuck Norcutt


On 2/23/2015 11:34 AM, Ken Norton wrote:
      Yes it does.  We proved that back in the B&W thread where the RAW photos 
came out exactly the same regardless of the Wratten filter that was used.

Lens filters CAN and DO make a big difference if you are needing to do
correction to equalize the RGB sensels. This is very evident when you
do highlight or shadow recovery.

Most camera sensors do not saturate equally. And even if they did, you
still have an issue with derived colors. In really, all colors are
derived colors, no matter what colors they are. Huh?

Let's take a pure red. Photograph it. If you look at the actual data
stored in the raw file, you'll see the red sensels getting
measurements, but the green and blue sensels at or near zero. However,
once converted, the three sensels are combined and a fuzzy math
applied to the conversion and red is no longer red. The histogram you
are looking at is almost certainly not that of the red sensels, but of
the red channel of a combined RGB pixel.

Still think I'm smoking dope? Well, do this. Put a Red #25 filter on
the lens of your digital camera and take some test pictures. Be VERY
careful to meter the scene before you put the filter on and take an
unfiltered shot. Lock the exposure down, shoot it with the filter.
Now, let the meter do its thing and shoot it again. Have fun doing
some +2/-2 brackets. Open the files up in your favorite raw converter
and start looking at your histograms. In fact, why don't you try doing
a monochrome conversion.

That is what is happening with your lovely flowers.

"Mommy? Why are those red tulips turning yellow?"

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