[argyllcms] Re: Measuring spectral transmission of lenses (and filters, too)
- From: Jan-Peter Homann <homann@xxxxxxxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Fri, 27 May 2011 15:59:54 +0200
Hello Iliah,
I don´t know how if you are doing professional work in this area, but
may be camSPECS from Image Engineering, could deliver some very
interesting inside views for your work.
... from the vendor...
camSPECS is a fast and affordable solution to measure the spectral
response of a digital camera system (access to RAW image files
required). It contains the hardware and software tools, which are
necessary to perform the measurement.
The light source is a modified slide projector with a stabilized power
supply, a special filtering of the light source and a customized optical
system. A set of 39 narrow-band interference filters is used to generate
the narrow-band light. The slide transportation system of the projector
is used to move the filters one after another in front of the lamp.
Beside the interference filters are neutral density filters, which are
used as a brightness reference to correct for exposure variations.
Exposure data is used to correct for different exposure levels. So it is
possible to perform the measurement even with the camera set to
automatic exposure control.
.... from the vendor ....
http://www.image-engineering.de/index.php?option=com_content&view=article&id=73&Itemid=63
Best regards
Jan-Peter
Am 26.05.11 04:48, schrieb Iliah Borg:
Dear Listmembers,
For raw conversion, I need to decide if I'm going to use lens / filters (polarizing
filters are my primary concern) correction matrices over sensor "profiles" or
not. To make up my mind I need to take measurements of spectral transmissions of
different lenses and filters. Instrumentation I have is: i1Pro and
Spectrolino/SpectroscanT. I'm not sure I can use the lamp in SpectroscanT (if you know it
is possible please advise so), so I started with i1Pro.
From reading argyll/spotread documentation it seems that I can use emission
mode, measuring separately the light source as a backlit and the light from the
same source passing through the lens; than calculate the transmission dividing
the pairs of numbers for each wavelength. As far as I understand no ambient
light attachment is needed in this case.
Another option would be to use -t flag, however only DTP41T and SpectroScanT
are listed for this flag (with the option to use Spectroscan with a separate
backlit light). Does this mode works for i1Pro too? An attempt to run it with
i1Pro caused no error messages, however the results are different from those
obtained through spotread with -e flag (might be of course because in a quick
experiment the lens was not placed to the same position).
Any comments and advice would be highly appreciated.
On a side note, running spotread from Argyll CMS 1.3.3 with -p flag /projector
measurement mode/ (OS X 10.6.7) returned "unsupported for my i1Pro.
--
Iliah Borg
ib@xxxxxxxxxxx
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