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01/25/2006 01:15:57 PM · #1 |
What's the difference between a circular polarizing filter and a linear polarizing filter?
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01/25/2006 01:22:06 PM · #2 |
| the one thing I know is autofocus won't work with linear polarizer. it only works with circularP. |
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01/25/2006 01:32:53 PM · #3 |
about $50.
and.. what gaurawa said.
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01/25/2006 01:34:35 PM · #4 |
How often do YOU need autofocus when your using a polorizer?
T |
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01/25/2006 01:37:48 PM · #5 |
Originally posted by Niten:
How often do YOU need autofocus when your using a polorizer?
T |
Often, if you do outdoor portraits or beach bikini shots
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01/25/2006 01:51:56 PM · #6 |
Originally posted by gaurawa:
the one thing I know is autofocus won't work with linear polarizer. it only works with circularP. |
I think that depends on the lens. On some lenses the front barrel doesn't rotate and therefore a circular polarizer is not needed. The need for the circ. instead of linear polarizer on some auto focus lenses is that the front barrel rotates thus requiring the filter to be re-adjusted. If I am not correct on this I am sure someone will correct me. |
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01/25/2006 02:29:04 PM · #7 |
Originally posted by AllgoodPics:
Originally posted by gaurawa:
the one thing I know is autofocus won't work with linear polarizer. it only works with circularP. |
I think that depends on the lens. On some lenses the front barrel doesn't rotate and therefore a circular polarizer is not needed. The need for the circ. instead of linear polarizer on some auto focus lenses is that the front barrel rotates thus requiring the filter to be re-adjusted. If I am not correct on this I am sure someone will correct me. |
that does sound reasonable. I will have to check it myself. If its true, then I just paid more when I could do with linear polarizer as the lenses I have all do back-focus and front end doesn't rotate |
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01/25/2006 02:35:41 PM · #8 |
Wondered myself after reading this just yesterday (had to go back and find it for you).
Polarizes come in two types:
Circular -- for all types of cameras: required for beam splitting metering systems commonly found in auto-focus SLR's and in most curretn TTL Slr's.
Linear -- for older metering systems.
This info from Tiffen 55mm Linear Polarizer Glass Filter
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01/25/2006 02:40:07 PM · #9 |
Originally posted by AllgoodPics:
Originally posted by gaurawa:
the one thing I know is autofocus won't work with linear polarizer. it only works with circularP. |
I think that depends on the lens. On some lenses the front barrel doesn't rotate and therefore a circular polarizer is not needed. The need for the circ. instead of linear polarizer on some auto focus lenses is that the front barrel rotates thus requiring the filter to be re-adjusted. If I am not correct on this I am sure someone will correct me. |
It has nothing to do with the rotating barrel on the lens. That affects polarization by rotating the filter and changing how the light is polarized. A lens with a rotating barrel will basically change the polarization setting as it focuses.
From Camerapedia.org --
Linear polarizing filters seem to have a greater effect on the final image than circular polarizers do, and in spite of many misconceptions, you can use either type of filter on any camera. But there is a catch: if you use a linear polarizer on a modern camera, you may not be able to use your built-in metering, or autofocus, or possibly both.
Modern autofocus systems use mirrors that act as beam-splitters: most of the light is reflected to the viewfinder for metering and viewing, while the rest (typically 25%) is transmitted and then reflected by a secondary mirror to the autofocus sensor, which is in the camera body. With a polarizing filter attached, the ratio of reflected/transmitted light (fixed for non-polarized light) varies with the polarization plane orientation of polarized light, relative to the beam-splitter, causing the amount of light reaching the autofocus sensor to vary. This effect can be particularly troublesome if your front element moves with the lens, as it would cause the amount of light reaching the sensor to change while the lens focuses.
While you can see (rather easily) when your autofocus system has been confused by a linear polarizer, there isn't such an easy way of knowing whether or not the internal light metering system has been stumped. The same loss of light principles that affect the autofocus system can also affect a camera's built-in meter, and obviously this is never good. What use is a light meter if it receives the wrong amount of light?
In both situations, a circular polarizer corrects the problem. Having removed the effect of linear polarization, the light functions normally inside the camera, in the beam splitter, and reaching the autofocus and metering sensors properly. Therefore, for your convenience, you should use a circular polarizer if your camera has autofocus or built-in light metering features. However, if you focus manually, and use a hand-held light meter, you can use a linear polarizer on any camera you wish.
Message edited by author 2006-01-25 14:42:38. |
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01/29/2006 07:08:02 AM · #10 |
Originally posted by gaurawa:
the one thing I know is autofocus won't work with linear polarizer. it only works with circularP. |
That is not true. I have always used a linear polarizer and my AF has worked just fine with all the cameras I've had..
June
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01/29/2006 07:11:07 AM · #11 |
Originally posted by AllgoodPics:
Originally posted by gaurawa:
the one thing I know is autofocus won't work with linear polarizer. it only works with circularP. |
I think that depends on the lens. On some lenses the front barrel doesn't rotate and therefore a circular polarizer is not needed. The need for the circ. instead of linear polarizer on some auto focus lenses is that the front barrel rotates thus requiring the filter to be re-adjusted. If I am not correct on this I am sure someone will correct me. |
If you use a circular polizer on a lens that rotates you still have to readjust the filter once you are focused because rotating the filter changes the effect of it. That is the case with every filter you use that is either graduated or needs to be places in a specific way.
June
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