Re: Densitometers and Spectrophotometers
Re: Densitometers and Spectrophotometers
- Subject: Re: Densitometers and Spectrophotometers
- From: Ray Maxwell <email@hidden>
- Date: Fri, 08 Feb 2008 20:07:02 -0800
Hi Mark,
Densitometers use filters that fade. Densitometers use an illuminate
that changes the spectral output with age. The spectral characteristics
of the sensor will change with age. The calibration chips used with
densitometers fade with time. Therefore densitometers that say they are
status T or I or E, etc. are not accurate after they have aged. The
calibration method and the design of the instrument cannot make accurate
measurements. They are fine for making relative measurements across a
press sheet. If you want to make density measurements that are accurate
and traceable to international standards, you need use a spectrophotometer.
A spectrophotometer is calibrated by using a special white reflector
that is very fade resistant. This white reflector is able to normalize
the illuminate and the spectral characteristics of the prism or grating
used in the spectrophotometer. Since the weighting factors for each
status T, I, E, and other filters are stored as digital numbers within
the instrument there is no possibility of fading or change. When I
worked with color scientists at Kodak, Imation, Dupont, and Fuji we
always used nothing but spectrophotometers and used a very involved
instrument meterology program so that we could accurately exchange
accurate density and Lab readings.
I remember that one of the color scientists at Imation told me that all
of their spectrophotometers were a hand picked and matched set of
instruments by Gretag Macbeth.
Ray Maxwell
email@hidden wrote:
In a message dated 08/02/2008 23:09:52 GMT Standard Time,
email@hidden writes:
I am not as happy with the repeatability of the Eye-One as I was with a
high end densitometer.
Matk sorry to butt in here - but doesn't a spectro calculate density
differently than a densitometer - or is that just an old wives tale
peter
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