BetterPhoto Q&A
Category: Camera Filters

Photography Question 

Sreekanth
 

Lens Filters


Purchased a Polarizing (circular) filter for my 28-105 F/3.5-4 USM Canon lens mounted on a elan 7e body (58 mm lens diag). Noticed that the view is quite dark with the filter on (tried rotating the polarizer with no setting being as bright as without the filter). Question is... the Polarizer does call for some f-stop adjustment, but the point is, it robs so much light that even with all the f-stop/shutter-speed massaging. The image is still darn dark when viewed through the camera. I have not yet taken a picture since it will be dark as well. Also turning the polarizer around did not seem to show any major changes at what I was looking (which was at several objects... ranging for sky, to leaves, lawn, flowers etc, at around 45 mins before sun-set.) Besides the fact they were all generally darker with the filter. Some advise needed please. Thanks.


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August 04, 2003

 

Jon Close
  The polarizer cuts light transmission by about 2 stops, meaning that only 1/4 of the total light comes through. That is normal. The exposure adjustment is needed only when you use a separate hand-held meter. Using the camera's built-in through-the-lens light meter with the filter in place you do not need to make any exposure compensation for the filter.

Rotating the filter changes the polarizing effect (cut glare/reflections, saturate colors), but will not change the amount of light transmission.


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August 04, 2003

 

Maynard McKillen
  Dear Sreekanth:
Appearances can be deceiving. While the polarizer can make the viewfinder image appear darker, if you meter a scene correctly, the image will appear at a "normal" brightness level on your print or slide.
Polarizers are designed to reduce reflections from nonmetallic/nonspecular light sources. (Specular light sources include the sun, candles, many types of light bulbs and other "pinpoint" light sources.)
If you'd like to see how dramatic the polarizer effect can be, pick a sunny midmorning or midafternoon location, point the camera ninety degrees away from the sun, and rotate the polarizer. The sky should darken noticeably during a portion of the rotation. The sky is, of course, a nonmetallic/nonspecular light source. The effect is reduced as the angle between the camera and sun drops below ninety degrees, but shows varying levels from ninety to two hundred seventy degrees, and drops off again between two hundred seventy degrees and three hundred sixty degrees.
You wouldn't necessarily notice a great change in images of flowers, leaves and a lawn unless you moved in close to photograph shiny portions of each on a sunny day.
Polarizers are frequently used to reduce reflections from glass and from the surfaces of lakes, rivers and ponds: all four can be nonmetallic/nonspecular light sources (the water will be if it is placid, i.e., not roughed up by wind). If the sun is reflected in the water, it is not be eliminated, since it is a specular light souce.
Similarly, if you were outside and pointed your camera at a window, and noticed the sun and clouds reflected in the window, rotating the polarizer could eliminate the reflections of the clouds but not the sun. The clouds and sky are a nonspecular light source, but the sun, reflected from the window surface, is specular, so it would not be eliminated.
A google search under "circular polarizer" will yield scads of information, including more technical explanations of how polarizers work.


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August 05, 2003

 

Sreekanth
  Jon & Maynard... thanks for your feedback & suggestions.

when you say "metered properly"... I guess one way to do this is to remove the polarizer, figure out the right setting and then put polarizer back on... preserving the settings.... OR .... is this even required. Will the camera figure this one out and compensate accordingly... or I take what the camera tells me and move out 2 Exposure levels (comp'ing for the presence of polarizer)?

Please advise.


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August 06, 2003

 

Jon Close
  The exposure adjustment is needed only when you use a separate hand-held meter. Using the camera's built-in through-the-lens light meter with the filter in place you do not need to make any exposure compensation for the filter.

You can do what you suggest, meter with the filter off, set the exposure manually adding +2 exposure comensation, then attach the filter and shoot, but that's really unnecessary.


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August 06, 2003

 

Chris A. Floden
  I have a Canon 10D (Digital SLR) and use a Hoya circular polarizing filter. I have the same problem with dark images as you describe and also notice no effect when I rotate the orientation of the filter. I know that the camera is supposed to compensate for these filters, but mine does not. I wonder if this is unique to my Canon camera or the Hoya filter?


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September 07, 2003

 

Sreekanth
  Chris:

I have not yet taken any photos with the polarizer yet... so cannot comment more on this one.. as to how the photos actually turned out. My comments/questions were only based on what was presented to me "TTL". I would've quickly experimented if I had a digital media.

Also.. per feedback above... this effect (of polarizer) can be bset appreciated based on certain angles. I will get back to you once I follow this and 'actually' take a few pictures.

did you try out these suggestions and still have no improvement ?

Sreekanth


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September 08, 2003

 
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