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Polarization filter - test.
3. Change of the exposure
2007-04-25
It's easy to notice the difference between particular photos after the study of the photographs from the previous page.
The shortest exposure time is for the picture taken without the filter (1/1000s). It means that sometimes it's impossible
to take a still photo without the support of the tripod due to extended exposure time when we use the filter (pic. 7,
pic. 10 - 1/20s). The problem doesn't relate to the photos 3, 4, 5 because time with attached filter is so short
that there is no possibility to move the picture (1/250s)
Excepting the risk of the motion blur of photo with the extended exposure time this doesn't really matters
for us - the photographers. Even though the exposure time was changed the image on the photo taken with the
filter won't differ from the picture without the filter regarding to the appearance. Excepting the changes due to the image polarization.
The thing is, that such a photo won't be overexposed or underexposed (pic.6, pic.7, the diagram in the middle part of the histogram).
Mode - preselection of the aperture, depth of field set on f/10. In spite of change of the exposure time the
photographs are exposed correctly - the diagram in the middle part of the histogram.
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fot. 6 without the polarization filter - the camera set the shutter time on 1/60s.
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fot. 7 with the polarization filter - the camera set the shutter time on 1/20s..
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However, such effect we can expect taking the photo in the manual mode, when we set the correct exposure time for
the picture without the filter (pic. 8), but later we attach the polarization filter without change of the exposure time
(pic.9 the histogram graph shifted to the left). Because the filter darken the image the picture will be underexposed
if we don't extend exposure time or we don't open the aperture wider.
Mode - manual, the depth of field set on f/10 , the time is the same in both photos 1/60s. The
photo with filter is underexposed - the graph shifted to the left.
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fot. 8 without the polarization filter - the exposure parameters set manually (1/60, f/10) - the photo exposed correctly.
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fot. 9 with the polarization filter - the exposure parameters the same as in the picture without the filter (1/60, f/10) - the photo underexposed.
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Just inversely is in the case if we set the correct exposition with the attached polarization filter (pic.10) and then we remove it without
changing the parameters - the photo will be overexposed (pic. 11 histogram graph shifted to the right)
mode - manual, depth of field set on f/10 the time is the same in both photos 1/20s.
The picture without filter is overexposed - the graph shifted to the right.
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fot. 10 with the polarization filter - parameters set manually (1/20, f/10) - the photograph exposed correctly.
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fot. 11 without the polarization filter - the parameters the same as in the photo with the filter (1/20, f/10) - the photograph overexposed.
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For this reason we have to be aware we will be forced to remove the filter if we don't want to use the tripod or we can't do it.
It's necessary to remember the attach or remove of filter need change of exposure in case of manual mode. The camera in the
automatic mode, semi-automatic or topical will set such parameters that there won't be difference in the photograph's
exposure even if there was the change of exposure time. The only difference will be in the temperature of the colours
and in the contrast caused by the polarization of the image, if the conditions allow the polarization.
 
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