[PDL]

Repeating UncleV's comments, circular polarizers were devised for digital sensors. snip...

Not true at all. I bought a circular polarizer for my first set of 35mm SLR's (Fujica) in the early 70's - long before digital was released. My first one was a Vivitar 49mm for the Fujica ESB lenses I owned and in the late 70's I bought one for my Vivitar 300mm (a TX model where I bought a Pentax K mount for it). I also bought two at 57mm for my Pentax Kit Lenses. I have used circular polarizers on nearly all of my camera bodies. I had one (read again 1) exposure issue with the kit lens while in NZ in 2006. Focus has never been an issue for me, either using AF on the Pentax cameras, including my SF-1, or the other models I use.

The Elitist - formerly known as PDL

[UncleVanya]

Not true at all. I bought a circular polarizer for my first set of 35mm SLR's (Fujica) in the early 70's - long before digital was released. My first one was a Vivitar 49mm for the Fujica ESB lenses I owned and in the late 70's I bought one for my Vivitar 300mm (a TX model where I bought a Pentax K mount for it). I also bought two at 57mm for my Pentax Kit Lenses. I have used circular polarizers on nearly all of my camera bodies. I had one (read again 1) exposure issue with the kit lens while in NZ in 2006. Focus has never been an issue for me, either using AF on the Pentax cameras, including my SF-1, or the other models I use.

The Elitist - formerly known as PDL

I'm not disputing you but as someone who took pictures since the early 1970s I never heard of circular polarizers until my pz -1 came out. I used gorgeous 52mm Nikon linear polarizers prior to that.

What was the occasion and how did you happen to get a circular vs linear polarizer at that time?

[PDL]

I was just out of High School and I had purchased my first true SLR (the Exa-Ihagge is not a "true" SLR ) in 1971. The polarizer was purchased in the mid 70's when I was dedicated to "Scientific" photography (see Field Photography and Handbook for Scientific Photography by Alfred A. Blaker). In college I majored in Anthropology (Archaeology/Physical Anthropology) with the hope of becoming a NG photographer in the end. However the circular polarizer was purchased to handle reflective objects and looking into water. I never saw a linear polarizing filter for sale in any of the photo shops I frequented. I did get polarizing sheets in my travels around Edmund Scientific and other such stuff.

Having worked in Archaeology labs and taken many, many slides of artifacts, circular polarizers are one of the tools in the chest. Circular polarizers give you the greatest flexibility as I see it. I remember reading about people using rotating polarizing filters in geologic thin section photomicrographic technique, stress analysis engineering (Scientific American cover January 1972) etc. etc..

The Elitist - formerly known as PDL

[philbaum]

All about Polarizers - Linear and Circular

If you have a partially reflecting mirror like modern DSLRs, this article indicates you need a circular polarizer.

But if you have a mirrorless, with no mirror :_), then you should be able to use a linear polarizer and save some bucks.
He doesn't say that specifically but after you read the article, you will see why.

[j0n4hpk]

Actually, I began hearing about the need for Circular Polarizing filters when I got my Pentax LX in the LXXXs (pun intended! ), because it's silicon photo diode exposure meter sensor will read wrongly with linear polarizing filters. I began getting them as needed since then.

[Kerrowdown]

hearing about the need for Circular Polarizing filters when I got my Pentax LX

You beat me to it... really screwed up meter readings otherwise.

[WPRESTO]

I remember reading about people using rotating polarizing filters in geologic thin section photomicrographic technique, stress analysis engineering (Scientific American cover January 1972) etc. etc..

The Elitist - formerly known as PDL

FYI: Polarized light has been used in petrography for a very long time. Some crystals will scatter or rotate polarized light in a characteristic way that enables identification of tiny mineral pieces in thin sections using a petrographic microscope. The latter is equipped with a calibrated rotating stage for measuring the degrees that polarized light is rotated. There are typically other kinds of filters that can be inserted. Some types of plastic, placed under stress or strain, will bend light that reveals, when viewed through a polarizing filter, the stress/strain lines within the plastic . In one application, a part is first made of such plastic, then forces are applied in the manner that the finished part will experience to determine where that part is most likely to fail, allowing modification of shape to deal optimally with those forces with minimal use of materials. Petrographic microscopes are still routinely used in geology, but I'm not sure about polarizing-under-stress/strain plastics in engineering since the advent of super-sensitive strain gauges and computer modeling.

[UncleVanya]

I was just out of High School and I had purchased my first true SLR (the Exa-Ihagge is not a "true" SLR ) in 1971. The polarizer was purchased in the mid 70's when I was dedicated to "Scientific" photography (see Field Photography and Handbook for Scientific Photography by Alfred A. Blaker). In college I majored in Anthropology (Archaeology/Physical Anthropology) with the hope of becoming a NG photographer in the end. However the circular polarizer was purchased to handle reflective objects and looking into water. I never saw a linear polarizing filter for sale in any of the photo shops I frequented. I did get polarizing sheets in my travels around Edmund Scientific and other such stuff.

Having worked in Archaeology labs and taken many, many slides of artifacts, circular polarizers are one of the tools in the chest. Circular polarizers give you the greatest flexibility as I see it. I remember reading about people using rotating polarizing filters in geologic thin section photomicrographic technique, stress analysis engineering (Scientific American cover January 1972) etc. etc..

The Elitist - formerly known as PDL

How did you know it was a circular not linear one? All of the photographic polarizers I ever saw in those days were round linear rotating filters. None were marked as such but that is what they were, later we learned how to test them to verify this when circular ones arrived.

Forgive me if I'm mistaken but it seems like you are confusing the shape of the filter with the type of polarization.

[PDL]

So the term Circular Polarizer printed on the side of the filter is wrong?

My bad --- Hey everybody - Vivitar LIES.

The Elitist - formerly known as PDL

[UncleVanya]

So the term Circular Polarizer printed on the side of the filter is wrong?

My bad --- Hey everybody - Vivitar LIES.

The Elitist - formerly known as PDL

You can be hard to converse with. I never said that. I asked how you knew and you failed to mention that. Further you stated that all of them were back in the day. Which is not my experience at all unless you mean round. It is easy to test.

[Digitalis]

please tell me the practical difference between these polariser types

The practical difference is that Linear polarisers transmit about 1/2 stop more light than the circular types.

[pathdoc]

The practical difference is that Linear polarisers transmit about 1/2 stop more light than the circular types.

Heh. Mere details. Dial in a correction and away you go.

[bdery]

If you have a partially reflecting mirror like modern DSLRs, this article indicates you need a circular polarizer.

Except if the mirror itself acts as a wave plate, which is pretty easy to do. And Pentax has been doing it for a while.

The practical difference is that Linear polarisers transmit about 1/2 stop more light than the circular types.

That is false, sorry.

Light transmission will be influenced by the choice of materials for the polarizer, the quality of the surfaces, their thickness, and several other factors. Not the fact that they are CP vs LP.

I use only linear for shooting with my K-3. Autofocus has no problems to point the target

[Not a Number]

I tested a linear polarizer on my K10D. While it did not through the AutoFocus off it would affect the exposure which would vary by rotating the filter a by about 1.5-2 EV.max.