Re: monitor/colorimeter bundles
Re: monitor/colorimeter bundles
- Subject: Re: monitor/colorimeter bundles
- From: Robin Myers <email@hidden>
- Date: Fri, 15 Feb 2008 06:04:18 -0800
On Feb 15, 2008, at 3:27 AM, Roger Breton wrote:
Hmm. Which instruments are "like the i1" in this regard? Does that
include the Spectrolino?
Good question. I'll admit I never tested the Spectrolino in this
regard.
Maybe someone else could comment? Until I find the time to try it,
personnally, that is, I wouldn't know. Maybe Mr. Myers has had some
experience with using the Spectrolino in emissive mode and could
comment?
Mr. Myers has extensively wrote sofware for the 'Lino -- and the
EyeOnePro,
too, of course.
Roger Breton
It has been many years since I used the Spectrolino for monitor
measurement and I do not remember how it fared with dim measurements.
For emissive lighting measurements I have run more recent studies.
Because since it does not have a cosine corrector, known as the
ambient filter with the i1 Pro, it is extremely sensitive to the
instrument's angle relative to the light source. Cosine correctors
also act as attenuators and without one the Spectrolino's sensor can
be easily over saturated. For that reason I use the i1 Pro in a
special rig I constructed to make emissive lighting measurements.
Back to monitor measurements. Whichever device you use for monitor
measurements, the usual way to get better data with dim signals is to
increase the integration time until a satisfactory signal to noise
ratio is achieved. This brings the signal above the shot noise (the
noise due to the random nature of light). There is a penalty for this,
the dark current noise is increased.
Before each set of emissive measurements the instrument will have the
user perform a calibration. For the i1 Pro this is accomplished in one
of two ways; for monitor measurements (without the ambient filter) the
calibration is performed by placing the instrument on the white tile,
for lighting measurements the calibration involves leaving the cap on
the ambient filter. In both cases the instrument's internal light
source is not activated, so the calibration is measuring the steady
state dark current noise, which will be subtracted from subsequent
measurements.
As the instrument is used for making monitor or lighting measurements,
the dark current noise level can change from the calibrated amount. A
number of factors can cause this; heat from electronics, monitor heat,
ambient room temperature changes, air moving over the instrument,
etcetera. This means that the more measurements made after the
calibration, the more likely the dark current value will change from
the calibrated amount, thus more error will appear in the dimmer patch
values.
There are ways to lessen this creeping error. Thermal chilling units
can be used inside the spectrometer to keep the sensor at a constant
temperature. A Photo Research PR-703 I used for several years had this
device. It also had a drying agent to remove the moisture condensing
from the chiller. The cost was also much higher than readers of this
list would pay.
Why a chiller and not a constant temperature heating element? The
reason is that the ability to detect small light amounts is increased
if the dark current noise is reduced. Astronomers use chillers for
their telescope sensors for just this reason. Sometimes resorting to
more exotic chilling methods such as liquid nitrogen.
Another way to lessen the dark current error would be to put a shutter
into the instrument and make a new dark current calibraton before each
emissive measurement. This would make monitor calibration a very slow
process. However, if the instrument is warming up considerably during
the monitor measuring sequence, this would lessen the dark current
error but the instrument might not be able to detect the dim monitor
signal.
A simpler method would be to put most of the dim patch measurement as
soon as possible after the dark calibration. I have not paid close
attention to the sequences used for calibrating monitors, but this
seems like a reasonable compromise.
There are other ways to improve the dim measurements that come to
mind, but I need to dash off now.
Robin Myers
_______________________________________________
Do not post admin requests to the list. They will be ignored.
Colorsync-users mailing list (email@hidden)
Help/Unsubscribe/Update your Subscription:
This email sent to email@hidden