 Robyn Gwilt |
77mm Polarisers I've been browsing B&H tonight, as I'd like a 77mm Polariser for my L lenses, but the variance is pricing is quite big - ie USD29 - USD190 + . I enjoy landscape photography, but its certainly not my fulltime money spinner - my question is, would I really be sacrificing major quality if I went for about a USD40 polariser. Bearing in mind that they drop, get scratched etc - is it better to replace a mid-price one every so often, than weep at replacing a really expensive one because accidents happen? Whats a good ND or Warm up filter (we have very harsh light here in South Africa) I don't know that I can really see the difference between say an 81a or b or c? Thanks
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Alan N. Marcus |
Hi Robyn, I have no firsthand knowledge regarding brands of polarizing filters. So please consider this marginal technical advice. The key attribute of a filter besides filtering is, optical flatness. It is more difficult to make a flat then to make a lens. An optical flat is exactly that -- flat -- all surfaces and all surfaces all parallel. It is easy to test a filter for flatness, just hold it in such a manner that the shiny polished glass becomes a mirror. Look at the reflected images of regular geometric shapes. I look at lines on the ceiling like the grid of a drop ceiling or the square waffle shape of a florescent fixture cover lens. As you gaze, wiggle the filter in your hand. If the filter is not flat you will see the reflected image wave and zigzag. Test both sides. Now hold the filter about ½ meter from your eye and look at a telephone or power pole. Look at the pole and wires as you rotate and wobble the filter. A good flat will give a steady view, a poor flat will cause the image to wobble and straight lines will appear curved. How a polarizer works: Think of the filter as a disk ruled with parallel straight microscopic lines. It functions like a jump rope stretched crosswise through a picket fence. One picket is missing and the rope transverses through this narrow slot. Now the rope can be plucked like a guitar string, but only in one direction i.e. up and down. A polarizing filter only allows light waves orientated with the ruled lines to transverse, all other waves are rejected. The polarizer darkens sky and increases saturation without changing color balance. The polarizer subdues reflections stemming from non-conductive surfaces like glass and paint. Water is basically a non-conductor so the polarizer reveals objects just below the surface. Polarizer’s work best with cross lighting. They are the most valuable filter used in color photography and they penetrate haze just like a UV filter. The filter mounting must allow the user to rotate the filter for effect. A coated filter transmits about 8% more light than a non-coated filter. Coating reduces internal reflections in an optical system. Important because a filter adds additional reflective surfaces. Reflections contribute to flare which can devastate an image. Two types of polarizing filters: Circular is two filters sandwiched together. First one is linier and filters out light rays not orientated with the filter. Second filter scrambles the rays so they exit with random orientations of vibration i.e. un-polarized. Some complex camera metering and focusing mechanisms use polarization in their optical systems. These mechanisms will be foiled by a linier polarizer. Does your camera need a circular? It’s a crap shoot. Will an expensive filter preformed better than a cheep one? I hope so! Will you see a difference? Probably not unless you are making giant over the mantle prints. Alan Marcus
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Robyn Gwilt |
Shoo Alan, you should work for Google or Wikipedia :) Thanks a mil - as always very informative! I tend to agree with your last sentence - that unless I'm making giant prints....... :)
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John P. Sandstedt |
Hi Robyn - There really isn't too much difference so long as you stay with the majors. I have polarizers from Hoya, Tiffen and B&W. But, if you go with the thin filters there are no threads onthe outside and so there's no stacking [for me a pain. Also, it's much more difficult to make adjustments while using a flower lens hood.
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Robyn Gwilt |
Thanks John - wasn't sure about B&W - don't think we get that brand here in SA. I agree re the petal hood - drives me mad!! I also noticed the 'thin' ones on B&H and wondered about that. Thanks both you and Alan :) Re my last sentence - what is a good ND grad filter - I'm really not sure of the difference - what is a soft vs hard grad? Thanks
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Alan N. Marcus |
HiRobyn, A natural density filter is one that reduces light energy. These are gray in color thus the term natural often abbreviated as “ND”. They are commonly used in optical systems to reduce exposure when stopping down the lens aperture is not an option. As an example, in portraiture one desires a wide aperture to minimizes depth-of-field. The scene is brightly lit and thus would normally overexpose. Exposing light is high speed flash so shutter control is not an option. Thus ND filter is imposed to reduce exposure while aperture remains untouched. ND’s are generally labeled using the density units. This unit is the industry standard. 0.00 clear glass A graduated ND commonly sold. The gray density material is made of gelatin dyed and sandwiched between two flats. Used to modify and perhaps enhance a blue-sky vista. The dye is not uniform but feathers top to bottom. It must be positioned further away from the lens for best effect, thus the background is filtered foreground is only lightly filtered. Hard vs. soft defines the degree of shading. A filter made of gelatin is common. Pure gelatin is dyed; ladled into a bath of cold water. Gelatin hardens and is scooped up from below using a square wire frame. Gelatin air dries. Only the center portion is usable and its optically flat. Finished filter is lacquered for protection. Result is high grade filter to be used in an optical path. All CC filters made this way (color correction). Lower grade is acetate base and must be used in lamphouse i.e. not in optical path. Alan Marcus
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Robyn Gwilt |
Thanks Alan - so if I got a polariser, I could maybe use it (when shooting water esp), in combo with an ND filter - say 0.30 medium, and that would be very effective - alternatvely using it on its own, would still be enough to notice the difference? Very often they're referred to as 81a or 81b - what does that mean? Tks
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Robyn Gwilt |
Then there is the Polariser with a warming filer built in - but wow its expensive - will cost me the same as my Light meter!!! http://www.bhphotovideo.com/c/product/181581-REG/B_W_65042853_77mm_Warm_Circular_Polarizer.html
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Robyn Gwilt |
Sorry guys, but any comments on this offer of a starter kit from B& H http://www.bhphotovideo.com/c/product/408020-REG/Hoya_GIK77GB_77_mm_Introductory_Filter.html Or just go for the polariser? To me this sounds like quite a nice deal? Thanks
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Alan N. Marcus |
The master filter maker was Frederick Wratten 1840- 1926. His company based in the UK was purchased by Kodak. Early filters were water solutions sandwiched between glass. Gelatin filters were dyed and sandwiched between glass. Mr. Wratten cataloged filters and assigned catalog numbers. 81’s are warming filters (conversion filters) to warm up bluish scenes. 81 is mildest followed by A - B – C 81 converts 3300°K to 3200°K
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Alan N. Marcus |
The Kelvin scale of temperature is embraced because it starts with absolute zero about -459 F° thus the scale has no negative numbers. Embraced by the lighting engineers it is the de facto standard used to specify color radiating from an artificial ligh source. Roughly the actual temperature of the glowing filament of an electric light bulb, stated in Kelvin units is approximately the color of output. Thus a normal service lamp operates at about 2800°K. Studio lamps are over volted meaning the are run at a higher than rated voltage to get more light as a coinsurance the light is bluer than standard service lamps. Studio (photo lamps) are either 3200°K or 3400°K while daylight at noon is about 6400 °K. Like glowing metal, as a lamp filament gets hotter it radiates less red and more blue. Hence the name Color Temperature. Film is made in batches. Some batches are adjusted for daylight others for tungsten illuminate. A modern digital can White Balance eliminating the need for the photographer to carry around a sack full of correction filters.
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John P. Sandstedt |
Alan - You forget to mention that the polarizer was invented by Dr. Edwin Land before he started the Polaroid Corporation. He held all the key patents and sold licenses to camera and lens makers. Robyn - If I had the cash I would only buy B+W filters, including the Kaesermann polarizer. The warming polarizer you describe is called the Moose Filter - it's a combination of a polarizer and an 812 filter. It cost less than the KAesermann. It's problem for me: it warms! And, maybe you'll want to impose no color impact on your image. I often use my polarizer and add a Tiffen ENhancing Filter to improve reds and oranges in our Fall foliage season. I also use a red 25A filter to get some great effects. You have to be careful how many filters you stack - usually two is the max. Robyn, I believe you use either a Canon XTi or 30D. I have a 72 mm Tiffen thin polarizer I bought for my Tamron 28-200 mm zoom lens. It's supposed to minimize vignetting. If I use it with any other lens it must be the last filter in the stack and I use a stepping ring to make the jump from 67 to 72 mm and, of course it has no threads. A minor annoyance. With my 30D and 17-85 mm IS zoom [at 17 mm = 28 mm traditional,] I get vignetting with this combination [Stepping ring to 72 mm polarizer.] I started a thread about this phenomenon and Jon Close wrote that he also didn't understand the vignetting either, especially since I'm using a stepping ring and thin polarizer. So, I have to keep this issue in mind when shooting wide angle shoot or try to correct the problem using the anti-vignetting tool in CS2.
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Alan N. Marcus |
A tip of the hat to John S, as always he hits the target and scores bull’s eye’s.
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Robyn Gwilt |
Thanks very much both of you - you're both very knowledgeable and informative, as always - much appreciated. Just remember that whatever the dollar price is, I have to multiply by roughly 7!! So price becomes an issue as USD199, becomes R1393.00, and then I need to add on another USD80 (R560.00), which becomes seriously expensive!! Thanks anyway - off to the coast for the weekend - so will look again for any other comments on Monday :) Regards
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