20D or 5D

In message coh.net,
(Philip Homburg) wrote:

In article , wrote:
In message coh.net,
(Philip Homburg) wrote:
Maybe a 'fog mode' is a good option for a consumer camera, but normally,
you compensate for errors in exposure meter using the exposure compensation
setting. There is no point in adding artificially low ISO settings just for
cases where the camera tends to underexpose.

You've got it all wrong. The cameras are leaving plenty of headroom by
default; you lose "extra" headroom by pulling ISO 100 to 50; not working
reflectance. In fact, if you shoot in RAW, pulling one stop has about
the same headroom as an unpulled JPEG with a normal contrast setting, on
most cameras.

So, you are saying that Canon cameras can be overexposed by one stop at the
lowest ISO setting?

If you're using a grey card or incident meter, yes. If you're just
setting the EC to +1 and blindly pointing it at mixed sun/shade scenes,
then you will blow the RAW highlights on some images. Different models
vary in their headroom. My 10D has far more headroom than my 20D in the
RAW data at ISO 100 with both cameras metered externally and manually
(same f-stop and shutter speed). The 20D makes an exception to its
general linearity of RAW data in the "extra" highlights at ISO 100 only,
which is missing about 0.2 stops, which it compensates for by ramping
the top zone to make it reach 4095, while keeping the midtones and
shadows linear.

This seems to contradict the measurements of Roger N. Clark
(in http://clarkvision.com/imagedetail/dynamicrange2/)
who saturates the sensor of a 1D mk II at +0.3 stop.

I don't see any real Exposure Index vs RAW value data there, at various
ISOs. All his output seems to be gamma-adjusted and white-balanced,
which is quite an abstraction from the RAW data. If you apply just a
gamma adjustment to RAW data, everything is very dark; it is
conventional to clip away RAW highlight in each channel, based
relatively, between the channels, on white-balancing.

I'd have to have a 1D mkII in my own possession to see what it's really
all about. There is a dearth of knowledge about all this stuff, as
people tend to draw conclusions from abstractions like JPEGs and TIFFs.
I'd like to see a library of RAW data based on external metering of
standard targets like the Kodak grey wedge and the Gretag-MacBeth Color
checker, or even blackframes, but everyone seems to treat RAW data like
a black box that only Adobe, David Coffin, and Michael Tapes, and the
camera manufacturers have any business looking at.
--


John P Sheehy

In message , I,
wrote:

I don't see any real Exposure Index vs RAW value data there, at various
ISOs. All his output seems to be gamma-adjusted and white-balanced,
which is quite an abstraction from the RAW data. If you apply just a
gamma adjustment to RAW data, everything is very dark; it is
conventional to clip away RAW highlight in each channel, based
relatively, between the channels, on white-balancing.

Here's a visual example. This color checker was shot in manual mode
with the Sekonic Incident readings for ISO 100, with the 10D set to ISO
100, on my terrace in blue-sky shade (making the blue channel very
strong and the red channel very weak). The color channels of this RAW
data were interpolated to full-res before downsizing the image, to get
rid of the checker-board pattern in un-interpolated RAW data. The RAW
linear range 0 to 4095 is mapped to 0 to 255 in the JPEG, without gamma
correction. See how dark the white square is:

http://www.pbase.com/jps_photo/image/48272307

It has well over a stop of headroom. One I did last night in
incandescent like didn't clip with the incident meter set to ISO 32,
with the 10D set to ISO 100. The meter perhaps has a yellow or green
bias.
--


John P Sheehy

wrote:

In message , I,
wrote:


I don't see any real Exposure Index vs RAW value data there, at various
ISOs. All his output seems to be gamma-adjusted and white-balanced,
which is quite an abstraction from the RAW data. If you apply just a
gamma adjustment to RAW data, everything is very dark; it is
conventional to clip away RAW highlight in each channel, based
relatively, between the channels, on white-balancing.


Here's a visual example. This color checker was shot in manual mode
with the Sekonic Incident readings for ISO 100, with the 10D set to ISO
100, on my terrace in blue-sky shade (making the blue channel very
strong and the red channel very weak). The color channels of this RAW
data were interpolated to full-res before downsizing the image, to get
rid of the checker-board pattern in un-interpolated RAW data. The RAW
linear range 0 to 4095 is mapped to 0 to 255 in the JPEG, without gamma
correction. See how dark the white square is:

http://www.pbase.com/jps_photo/image/48272307

It has well over a stop of headroom. One I did last night in
incandescent like didn't clip with the incident meter set to ISO 32,
with the 10D set to ISO 100. The meter perhaps has a yellow or green
bias.

Can you find the "natural" (neutral gain) ISO of the sensor?


--
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-- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
-- [SI] gallery & rulz: http://www.pbase.com/shootin
-- e-meil: Remove FreeLunch.

In article , wrote:
In message , I,
Here's a visual example. This color checker was shot in manual mode
with the Sekonic Incident readings for ISO 100, with the 10D set to ISO
100, on my terrace in blue-sky shade (making the blue channel very
strong and the red channel very weak). The color channels of this RAW
data were interpolated to full-res before downsizing the image, to get
rid of the checker-board pattern in un-interpolated RAW data. The RAW
linear range 0 to 4095 is mapped to 0 to 255 in the JPEG, without gamma
correction. See how dark the white square is:

http://www.pbase.com/jps_photo/image/48272307

It has well over a stop of headroom. One I did last night in
incandescent like didn't clip with the incident meter set to ISO 32,
with the 10D set to ISO 100. The meter perhaps has a yellow or green
bias.

Before trying all kinds of weird color temperatures, it might be useful
to start with more common ones, such as D50.

I don't have absolutely no idea how a Sekonic lightmeter responds to overly
blue light.


--
That was it. Done. The faulty Monk was turned out into the desert where it
could believe what it liked, including the idea that it had been hard done
by. It was allowed to keep its horse, since horses were so cheap to make.
-- Douglas Adams in Dirk Gently's Holistic Detective Agency

In message ,
Alan Browne wrote:

Can you find the "natural" (neutral gain) ISO of the sensor?

Define it, and I will find it.
--


John P Sheehy

In message coh.net,
(Philip Homburg) wrote:


Before trying all kinds of weird color temperatures,

What is "weird" about daylight shade, or warm indoor lighting?

it might be useful
to start with more common ones, such as D50.

I've never heard that terminology before. Is that sunlight?

I don't have absolutely no idea how a Sekonic lightmeter responds to overly
blue light.

Am I the first to use one in shade?
--


John P Sheehy

In message coh.net,
(Philip Homburg) wrote:

I don't have absolutely no idea how a Sekonic lightmeter responds to overly
blue light.

The color of the white square in the JPEG is not the color of the light,
if that's what you thought. Real-world white objects in white light are
cyan to green in most CFA DSLRs.
--


John P Sheehy

In article , wrote:
In message coh.net,
(Philip Homburg) wrote:

I don't have absolutely no idea how a Sekonic lightmeter responds to overly
blue light.

The color of the white square in the JPEG is not the color of the light,
if that's what you thought. Real-world white objects in white light are
cyan to green in most CFA DSLRs.

It doesn't matter. It was specified that the shot was not taken in
normal daylight.


--
That was it. Done. The faulty Monk was turned out into the desert where it
could believe what it liked, including the idea that it had been hard done
by. It was allowed to keep its horse, since horses were so cheap to make.
-- Douglas Adams in Dirk Gently's Holistic Detective Agency

In article , wrote:
In message coh.net,
(Philip Homburg) wrote:
Before trying all kinds of weird color temperatures,

What is "weird" about daylight shade, or warm indoor lighting?

it might be useful
to start with more common ones, such as D50.

I've never heard that terminology before. Is that sunlight?

Yes, a reference 5000K sunlight.

I don't have absolutely no idea how a Sekonic lightmeter responds to overly
blue light.

Am I the first to use one in shade?

Probably not. But in the film world, you add a color conversion filter and
you add some stops for the loss of light. Usually it is smart to bracket
in those conditions. But you may get away with holding the CC filter in
front of your lightmeter's sensor.

ISO is defined at a specific color temperature (usually 5000K). In all other
situations (without CC filters) you may end up with completely different ISO
values.


--
That was it. Done. The faulty Monk was turned out into the desert where it
could believe what it liked, including the idea that it had been hard done
by. It was allowed to keep its horse, since horses were so cheap to make.
-- Douglas Adams in Dirk Gently's Holistic Detective Agency

In message coh.net,
(Philip Homburg) wrote:

In article , wrote:
In message coh.net,
(Philip Homburg) wrote:

I don't have absolutely no idea how a Sekonic lightmeter responds to overly
blue light.

The color of the white square in the JPEG is not the color of the light,
if that's what you thought. Real-world white objects in white light are
cyan to green in most CFA DSLRs.

It doesn't matter. It was specified that the shot was not taken in
normal daylight.

How much of a difference do you think that would make? Between my two
extremes (incandescent and shade), the ISOs as measured for
reflectance-only for the white square was perhaps ISO 30 vs 40, both far
from ISO 100.

I just tried it now with my 550EX flash, in manual mode, based on the
guide number; f/22 at 8.23 feet from flash to target with 105mm zoom.
The green channel predominates here, with blue at about 80% of the green
RAW values, and red at about 50%. The average green value in the white
square is about 1520. The blackpoint of the 10D at ISO 100 is about
126, so that leaves us 1494 RAW values for the 90% reflectance square
That would put 100% at 1660 above blackpoint. The 10D clips at ISO 100
anywhere from 3997 to 4005 or so (depending on pixel column), so the
maximum above blackpoint is about 3875. 1660/3875 = 0.43, or ISO 43, if
the standard is 100% reflectance. Now, I shot this in a white hallway
28" wide from 8.2 feet, so there is some extra light bouncing off the
walls, so the actual value is actually lower, although the practical
value in a narrow white hallway is about right.
--


John P Sheehy