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Old Jun 14, 2006, 9:35 PM   #1
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Ordered my *ist DL last Friday, and the Tiffen filter set arrived today. I've heard that some people received bad circular polarizers from them, so I wanted to check. How can I tell? I've spun both parts, looking through from both sides, but it doesn't change tint. But it is a circular polarizer, which I assume means it's a set of concentric micro-lines and may not work that way. Any suggestions? (And I looked for a filter forum, but couldn't find it).
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Old Jun 14, 2006, 11:02 PM   #2
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I assume that circular polarizers work the same way as linear ones (that's all I have). If so, how much change you notice depends on where the sun is in relationship to the filter. If you are standing with your back to the sun and twist the ring, you won't see much difference. If you stand with the sun on your shoulder (the camera will be at 90 degrees to the sun) and twist, you should see it get a bit darker or lighter. Another way to check is to point the camera to some shiny leaves that have glare from the sun. Turn the outer ring and see if it lesson's the glare.

I bought a circular polarizer at Best Buy (think it was a Conkin) and it didn't do much of anything. It wouldn't do much for the shine off of leaves, and didn't seem to make any difference with the sky. I don't know if that's because it was a lousy one or if it's because the circular polarizers work differently than linear ones.

Has anyone ever tried to use a linear polarizer with an AF lens on an *ist camera? My 2 AF lenses are 52 and my filters are all 49, so I haven't tried it.
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Old Jun 15, 2006, 5:50 AM   #3
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I am not sure about the Pentax digital SLRs but most previous film AF SLRs used a semi silvered mirror to direct some light to the AF sensor. Since this effectively polarized the light, a linear polarizer could cause the AF system to "go blind". Circular polarizers work in the same manner, photographically, but do not cause this effect.

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Old Jun 15, 2006, 11:07 AM   #4
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I recently bought Hoya cir-polarizing filter and have 2 questions.

1. Is it normal for all the pictures to come out underexposed?
2. Does each side of the filter have a different coating?

The reason I ask about the coating is that I can clean the 'outside' side fine and its perfectly clear and smear free.
However when I clean the inside it never comes clean, there is always smears.
I use the same cleaning cloth to clean my lenses/filters with no problems at all, just 1 side of this polarizing filter which is causing probems.
Any ideas?
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Old Jun 15, 2006, 11:46 AM   #5
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I hope one of the experts jumps in here, because I'm no expert on this, and have only used linear polarizers bought in the '80s.

However, in answer to your first question - my personal experience with linear polarizers has been that the camera won't meter wrong just because you use the polarizer. They always act as a ND filter, but my camera has always compensates the exposure. If you are shooting completely manual and not letting the camera meter, you could easily underexpose, but my DS has always compensated well (I always let the camera figure out the shutter speed).

The reason I asked about whether anyone had tried a linear polarizer with the *ist cameras is that I used to own an FZ30. There were a number of people who used linear polarizers with them, so however that camera focused wasn't affected. Just wondering if anyone had tried it.

I can't answer your second question about the coatings, because I'm clueless on this one. I would guess that it shouldn't work the way you descibe and that you have a bad filter, but I don't know that for a fact at all.
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Old Jun 15, 2006, 12:59 PM   #6
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I typically have to compensate by as much as 1 to 2 stops when I use a polarizer.
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Old Jun 15, 2006, 1:52 PM   #7
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mtngal

It was the semi reflective mirror of the AF film SLRs that caused the problem, it polarized the light. Adding a linear polarizer on top of that could result in cross polarization for the AF sensor, thus it was blind. Digicams such as the Panasonic do not use a mirror and use the sensor to autofocus (so I oversimplify), this means it is not affected by a polarizer of any type. I regularly used a linear polarizer with my Fuji S7000 since it was uneffected. See http://www.mir.com.my/rb/photography...axxum7k/AF.htmfor more information.

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Old Jun 15, 2006, 4:04 PM   #8
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Thanks for the answer - I actually tried an experiment before I read your response. If I understand this correctly, in AF filmcameras, they treated the mirrors to cut down on the reflection/glare off of it so that the AF mechanism could function better with plain lenses. If you introduce a polarized lens, they can cut out all the light - the polarizer blocks all light except for in one direction, then the mirror cuts the light from that direction which cuts out all light for the AF mechanism. So (if I have this right) if the mirror isn't treated a linear polarizer would work.

Before I read this, I tried an experiment. My Phoenix macro lens finally came in today (it was backordered). My hubby did get the AF version, and I'm glad he did, though I don't know how much I'll use the AF (not at all with the adaptor on it- it really has trouble). This lens has 49 threads, so I put on my polarizer (marked Hoya PL - no mention of cir on it, and I'm pretty sure this is the one I bought back in the early '80s) and used the AF to focus on some ground cover about 10 feet away. No problem - lock almost immediately.
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