[argyllcms] Re: Measuring spectral transmission of lenses (and filters, too)
- From: Iliah Borg <ib@xxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Fri, 27 May 2011 11:12:24 -0400
Dear Jan-Peter,
I do know of this solution. I actually built a very similar one (with a better
light source) couple of years ago, and nearly all generic camera profiles for
RPP are calculated using it. However, for lens profiling it is not a good one,
adding too much hassle to measure SPD for each filter and combining those. A
~$2000 monochromator might be an easier solution than, as now we are not
limited with sensor sensitivity to 9mkW radiation power ;) I'm actually looking
for a more straightforward solution, like a halogen lamp and a decent
spectrophotometer. Paying ~$10,000 for a spectroradiometer to support a free
raw converter seems a little excessive ;)
On May 27, 2011, at 9:59 AM, Jan-Peter Homann wrote:
> 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
>>
>>
>>
>>
>>
>
>
> --
> ---------- Please note the new adress --------------
>
> homann colormanagement --------- fon +49 30 611 075 18
> Jan-Peter Homann ------------ mobile +49 171 54 70 358
> Cotheniusstr. 3 -------- http://www.colormanagement.de
> 10407 Berlin -------- mailto:homann@xxxxxxxxxxxxxxxxxx
>
>
>
--
Iliah Borg
ib@xxxxxxxxxxx
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