Dear All
I was working with a Fotonowy MFT last year, and it showed some instability which seems to be related to the spectrometer. What it looked like was as follows:
- Place a clean 99% Spectralon standard under the beam.
- Auto focus.
- Run for two minutes.
- The dE00 graph for the white balance rose to about 0.1, the rate of change decreasing as time went on.
The unit was fully warmed up, and repeating the test five times with two different full-spectrum LEDs in changer the gave similar (although not identical) results..
I ran some 10 minute tests, and although the rate of change of the dE00 value continued to decrease after the first 2 minutes, it did not come to a constant value. I replaced the Spectralon reference with a power meter, and ran some more two minute tests. The actual power of the light source looked pretty constant, so I infer that the problem is with the spectrometer. I then ran tests on 50% and 2% reflectance standards, all of which showed similar instability - the 2% standard was a little worse.
Now, we all know that dE00 is not a meaningful measurement for the white reference - there is clearly a change here, but the magnitude is difficult to interpret. Nonetheless, this is the first time I have seen this size of instability in an MFT unit just looking at a white reference. Has anyone had any similar experiences, either with the Fotonowy or another unit?
JP
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JP Brown
Senior Conservator
Field Museum
Chicago
United States
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