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Old June 14th, 2002, 08:26 PM   #1
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polarizer question

When I picked up my 3x lens today, there was also a used (but mint) heliopan polarizing filter, which I bought for $100.

It wasn't until I got home that I noticed that it said linear on the case.

Now I know I should have gotten a circular polarizer, but they had it mounted on an XL1 so I didn't think to check. Can this still be used to full effect? What bad things will happen if I use it? Should I just put it up for sale on Ebay?

Thanks
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Old June 14th, 2002, 11:40 PM   #2
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Hi,

The use of a linear polarizer may affect the auto focus and exposure. Sell it on ebay.

Jeff
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Old June 24th, 2002, 04:03 AM   #3
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I was in a photography shop at the weekend looking at filters. I've read numerous times on this site about getting a circular polariser for use outdoors.

When I asked the guy in the shop about it he was VERY adamant that I should NOT get a circular polarizer but that I should get a linear polarizer. Was he talking rubbish?
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Old June 24th, 2002, 06:18 AM   #4
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Justin,
I have had the same problems with "Photography" shops. All they usually know about, are still cameras. There is often a world of difference between the two, and polorizing lenses is one of those issues.
DO NOT BELIEVE ALL THEY TELL YOU!

I live in a less than major city, and nobody here has any idea what video is, and have never even heard of my XL1s. Therefore, I have to order all of my stuff, usually online. Again, in this case, DO NOT BELIEVE ALL THEY TELL YOU!

Ask here, buy where it is recommended.
Keith
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Old June 24th, 2002, 06:35 AM   #5
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The use of a linear polarizer will adversely effect your auto focus. The auto focus works by analyzing the contrast in the scene. If a scene is dark or poorly lit (low contrast) the auto focus is slow or it hunts for the proper focus. In properly lit or bright scenes the AF works well unless confused by solid objects or certain patterns. The AF will have a hard time focusing on a solid white wall because of the lack of contrast. The crystalline structure, or pattern, of the linear polarizer confuses the AF and can cause it to hunt for the focus.

Jeff
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Old June 24th, 2002, 08:53 AM   #6
 
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1. NEVER use auto-focus
2. the ONLY reason for a circular polarizer is for video cameras that have a rotating front element during focus(manual or otherwise). A linear polarizer will work just fine on an XL1(no rotating front element). Just turn that worthless auto-focus off.
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Old June 24th, 2002, 11:07 AM   #7
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Well, I must say I find my circular polarizer quite handy. I can just
turn the front ring towards the best setting without it screwing
off. When looking at a car window for example, I can rotate the
thing from transparent to "mirror" and anything in between.
Quite handy.

Some people need auto-focus bill. If your doing run and gun
it is pretty difficult to focus as well.
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Old June 24th, 2002, 08:27 PM   #8
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Light rays, from any source, contain wave fronts, which radiate in all directions at right angles to the direction of travel of the ray. Light falling on certain surfaces (shiny surfaces like water, glass, paint etc.) cut out all but those rays parallel to that surface, producing what is called polarized light. Polarizing filters contain tiny crystals all lined up in parellel (linear Polarizer). When turned perpendicular to the reflecting surface, they block out the unwanted, polarized, reflections, and pass the rest of the light. A polarizing filter is also useful in reducing the reflections from plants and other objects, resulting in better color saturation. It also acts as a ND filter by cutting the light by 2 1/2 stops.

Dull or matte surfaces like sand, paper, and bare metal DO NOT polarize light. Snow, ice and water do polarize light. The blue sky creates a band of polarized light at an angle of 90' to the sun. To locate the band in the sky point your index finger at the sun, with your thumb extended straight out (at a 90' angle) and it will point to the polarized band in the sky.

Cameras (still, digital and video) with metering and auto focusing systems that have a split beam or reflective glass surface between the filter and the meter (and AF sensor) will be adversely affected by a linear polarizer. In these cases a circular polarizer must be used. You can detect this condition by rotating the linear polarizer and checking to see if your exposure (aperature or shutter speed) changes by more than 1 stop as you rotate the filter. Turning the circular polarizer will produce no change in exposure. The linear polarizer affects focus as I mentioned earlier.

Jeff
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Old June 25th, 2002, 11:30 AM   #9
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There's more than a few inaccuracies on this thread!

The only autofocus affected by a linear polarizer is a split beam and not a contrast driven system.
Both circular and linear polarizers will be affected by the rotation of the filter.

A circular is a linear with a 1/4 wave retarder on the back of it. Both operate in exactly the same manner.

While there is no real reason to spend the extra on a circular most people err on the side of caution, either through ignorance or fear. I just called tiffen and the customer service rep said that only cameras that use a split beam or a video tap as found on some broadcast cameras would require a circular.

If we repeat here say enough it eventually is perceived as truth. As sure as I am about this and other topics I ALWAYS double check my facts before posting. It is enought to drive anyone nuts though. We have reps from Sony and Canon making the same mistake and swearing to it as gospel.

there is a paragraph on the circular vs linear at
http://www.tiffen.com/ultrapol.htm
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Old June 25th, 2002, 02:42 PM   #10
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Ah...
So...
Does this mean the linear polarizer I bought will work fine with my XL1? Should I keep it?
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Old June 25th, 2002, 02:51 PM   #11
 
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That's what I said. How many times do I gotta say it?
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Old June 25th, 2002, 02:54 PM   #12
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I would say so. That's one fine filter.
A circular will cost you double and for what end?
If you don't believe me try it out.
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Old June 25th, 2002, 02:58 PM   #13
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Oh I tried it out when I got it and it seemed to work fine.
You guys know a heck of a lot more than me about XL1's and such, so I would defer to your experience if everyone said to ditch it.
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Old June 25th, 2002, 03:22 PM   #14
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It is good to question standard answers, because that is how we can all learn. At the recent Canon Digital Solution Forum in Tampa last year I posed this same question to a Canon Rep. showing the XL1S. Is a circular polarizer required for the XL1? The Rep responded with well that's a good question let's ask one of the experts. He proceeded to round up a Japanese gentleman who was introduced to us as part of the Technical Service Team. Through an interpetor he was asked about linear and circular polarizers. What we were told through the interpetor was that a circular polarizer is recommended because the prism block and CCD block contain dichroic filters and a beam splitter and a linear polarizer could affect the performance of the camera. While I don't speak Japanese, his answer and my gut feelings (20+ years of experience) have me convinced to use a circular polarizer.
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Old June 25th, 2002, 04:39 PM   #15
 
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Dichroics pass or reflect light depending on the wavelength. A dichroic is used to reflect some of the incident light to the light meter, while the rest is passed on to the CCD. Now, the question is whether the dichroic is polarization sensitive or not. It depends on the polarizer. So, it would appear that in some cases, the light meter may or may not be affected by the polarizer. I never thought of using a light meter seperate and distinct from the CCD.

Interesting input...I never thought of it that way. Thanx.
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