> Yes, I was doing just that. Old school syndrome. The question now is
> how much underexposure should be applied, or just take a reading without the
> filter and then shoot with the filter and no adjustment?
Expose it exactly as you would with no filter. DO NOT add exposure.
However, I would "ETTR" (Expose to the right) as much as you dare.
That's hard to do without an external spot meter, though. Without the
ability to see the histogram of the RAW file, you're totally lost.
BTW, if you haven't done so already, download RawDigger. It will be
usable for 30 days or something like that before you need to pay for
it, but it is extremely revealing as to what is going on inside the
sauce pan.
>From a practical perspective, forget the lens filters entirely, when
shooting digital. From a research perspective, have at it.
There is a side to all this which is very good to know. When shooting
sunsets/sunrises or things that are very saturated in red, blue or
green, it's easy to overexpose one of the color channels. The problem
is that you'll never see it happen in the histograms unless the
histograms show you raw data. Unfortunately, NONE of the unhacked
cameras do that. And in the computer, basically RawShooter is the only
program that gives you this ability either.
When looking at the histograms in camera or in computer, they are
ALWAYS (except as above noted) post demosaic. Why is this important to
know? See this:
Triplet values used for demosiac:
R=128
G=128
B=128
Merge the three together and you get a mid-tone gray with an RGB value
of 128:128:128. The histograms show what you would expect.
Triplet values used for demosiac:
R=128
G=0
B=0
Merge the three together and you may end up with an RGB value of
43:0:0. The histograms will show the pixel value two stops low.
As the on-screen/lcd histogram is showing the value two stops low,
you'll be tempted to boost the camera exposure by two stops to
compensate. The problem with that is that you now are blowing the snot
out of the red sensels.
So, let's take this to the applied conclusion:
1. Shoot the scene with the lens filter with the proper exposure of an
UNFILTERED lens. If you are in sunny-16 conditions, shoot sunny-16. DO
NOT add exposure to compensate for the filter. (the resulting image
will LOOK underexposed)
2. During raw conversion, convert to 16-bit per channel.
3. Apply brightness and contrast adjustments post-conversion to bring
everything back up to full brightness range.
4. Enjoy.
Why is this important to know? Because when we shoot sunsets and other
fully saturated color scenes, the needs of the three-color array of
the sensor do not match the ways the metering and demosaicing works.
The metering uses tri-color mixing, which will result in scenes
getting over exposed. We see this all the time with sunsets or with
shooting roses and tulips. Stuff that is intense red. The red sensels
are clipping and you never even have a clue. Based on my own research
using the Red #25, I've confirmed my own observations that in order to
photograph a red rose or tulip, you need to underexpose by up to two
stops.
Yes, we fix it in post. But you've got to capture the bits first.
--
Ken Norton
ken@xxxxxxxxxxx
http://www.zone-10.com
--
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