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Re: [OM] ETTR with the Sekonic L-508

Subject: Re: [OM] ETTR with the Sekonic L-508
From: Ken Norton <ken@xxxxxxxxxxx>
Date: Thu, 13 Oct 2011 09:11:15 -0500
> The exposure is properly balanced over the RBG channels so less chance of
saturating the Red in giving adequate exposure to the Blue.  This means that
each channel is operating in the same exposure region of it's
"characteristic curve" - compare this with film.  The end result being that
the noise should be more equally distributed across RGB channels and I
expect this has some benefit in reducing noise reduction artifacts.


Thanks, Wayne. That was what I was trying to say, but was rather clumsy and
incomplete in my explanation.

By making the incoming image as "daylight balanced" as possible, we are able
to maximize the bit depth of all three color channels. When shooting in
tungsten lighting conditions, if we take the red and green channels up to
maximum clip point, the blue channel will be up to two stops down. This
reduces the dynamic range of the blue channel. So, during conversion, we'll
boost the blue channel to balance the scene, but there is no free lunch and
we'll either end up with more chroma noise or a noticeable loss of color
integrity in the shadows. Typically, we'll get that dreaded blue haze in the
shadows which is the bane of compact cameras.

In the case of the E-1, red/yellow clipping is a problem. Any attempt to
ETTR under non-daylight balanced lighting will almost certainly result in
clipping. Depending on the raw converter, this is either a nuisance or an
all-out picture-destroying trait. This is one reason why I've been an
advocate for shooting for final output, not for raw conversion. By using a
corrective filter on-lens, instead of correcting during conversion, we run
very little risk of asymmetrical clipping.

So, you ask, why isn't the Schnozz using an on-lens corrective filter?
Several reasons come to mind:

1. New filters for each size lens. The art of using a common size for all
lenses within a lens family is long since lost on the manufacturers. My OM
Zuikos are all 49 or 55mm, except for the super-teles. In the case of
digital, I've yet to experience any two lenses with the same filter size.

2. Flash. When it really matters (weddings, events, etc), I'm using flash to
control my lighting anyway.

3. Convenience. Lighting conditions can change rapidly during a wedding,
event, etc. shoot. "Fixing it in post" is much easier and faster than
interrupting the shooting flow by constantly needing to screw and unscrew
filters.

4. Color misbalance. Digital doesn't respond the same to mixed lighting as
film does. A filter corrects the blue-orange shift, but some digital cameras
have a blue-red shift. I still had to correct color balance in post.

I have found it quite interesting how my three digital cameras respond to
tungsten lighting. When correcting for white-balance, we get color shifts in
different portions of the tonal range. When adjusting WB for a known midtone
(gray card, Expodisc, etc), the A1 will get greenish shadows. The E-1 does
pretty well, but the L1 can take on a sickly look as the blue/orange vs
blue/red shift is not very friendly. (The Olympus PEN series is very good in
this regard when shooting in-camera JPEG).

I have just a few rolls left, but I think Fujifilm 800 NPZ did a very fine
job of handling color-correction for tungsten lighting. In fact, when it
comes to mixed tungsten/florescent lighting, Fujifilm's four-color layer
films simply ruled! Kodak's new Portra 400 is also very good. In my opinion,
either of these films handle mixed lighting better than any digital camera
I've seen. With digital, once you correct for skintones, the rest of the
scene goes to pot. With either of these two mentioned films, you can have
both looking good.

AG
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