How is an adjustable polarizer adjusted for maximum preformance? And is there a single lens Polarizer? What I mean is what do you see through an SLR when it is adjusted right. [ 03 March 2002, 21:01: Message edited by: Art ]
Hi Art, With a circular polarizing filter, as you turn it clockwise or counter-clockwise, you will see contrast vary. A good example for use is on a cloudy day. As you turn the filter, you see the details of the clouds more, or less enhanced. You may choose to take your shot at any point it looks good to you. I think it's the greatest filter in the bag, but I keep one on each of my lenses almost 100% of the time. I hope this helps!
Mark. Can the polarizer also be used on a bright sunny day? If so what do I look for through the SLR? And what is the cost of an adjustable polarizer the box says 67 mm and the lens is a 100-400 mm auto focus long lens f/4.5-6.7-f/22-32. [ 04 March 2002, 20:14: Message edited by: Art ]
Polarizers come in two flavors that I'm aware of. The original polarizers had a direction that they polarized the light. This meant that for best performance you ended up orienting the filter or twisting it "towards" the sun. They had an arrow on the ring of the filter to indicate which direction the filter was oriented or pointed. You could twist it around to get the effect that you wanted. As I understand it, the new circularly polarized filters have no orientation, so they don't need to be rotated. The filters act just like a set of polarized sunglasses. Whatever glare you could hope to cut down using polarized sunglasses, you'd also see using a filter. This is especially good photographing stuff with reflections, such as water, snow, and shiny cars. Less of a benefit photographing landscapes and plants. It typicall reduces the light by two f-stops. The size of the fillter is determined by the diameter of the lens, not its focal length. For instance, my 135 mm lens has a focal length of 135 mm, but takes a lens diameter of 62 mm. My 50 mm focal-length lens takes a lens diameter of 48 mm. They're a great filter. I recommend everyone have one to add to their arsenal of camera gadgets. Mark
Circular polarizer filters do twist but (IIRC) do not have a marking that denotes an 'orientation' - twisting circular polarizers will change the intensity of the polarizing effect. Choice of linear v circular is determined by your camera's focus and/or metering system - not by you I'll try to explain this the best I can. When light passes through the air it is reflected and or refracted in many different directions. The reason that the sky near the horizon appears whiter than the sky directly overhead is because the light has traveled though more air to get to you and is reflected in more directions. A polorizer filter will only allow light traveling in one direction through it. If you look through a polorizer and turn it, you will see the sky change from light blue, to very dark blue and back again to light blue. Now, when light bounces off a surface such as the hood of a car, water, or even the desert floor it will be oriented in only one direction and you (and your camera) will see that as a very bright glare. Polarized sunglasses are designed to not allow light reflected off the surface of the earth (water, road, etc) and Polorizer filters can be oriented to not allow light traveling an any one direction through - you can remove the glare off the water, or remove the reflection off of window glass. I can’t tell you technically what is different about a circular polarizer - but I can tell you some camera metering systems (many of Canons) and almost all auto-focusing systems can be tricked by linear polarizer filters. Circular polarizers are designed to not trick these light metering and focusing systems. I don't know how much 67mm polarizer filters cost. I would recommend stopping in or calling your local camera shop - they can tell you what type of polorizer you camera needs and they can also show you one so you can see what they are capable of.
