Quick Tip - The Circular Polarizing (CP) Filter

Water Lily

The Circular Polarizing (CP) filter is a simple tool that should be in every photographer’s bag.  And, if you are a serious amateur photographer, or pro, you most likely have one in your bag already.   This unique filter is attached to the front of the lens and can be used to remove unwanted reflections, enhance colors and create dramatic skies.  This Quick Tip is about how and when to use this filter.

Without getting too technical, every object outdoors reflects light from the sky more or less diffused and largely polarized. Often some objects can appear to have a bluish cast and be dull in photographs.  The main functions of the polarizing filter include: enhancing the color of a subject by blocking this ‘blue veil’ of light from the sky; and to control reflections.  The subject that you are shooting will display maximum  polarization at right angles to the sun’s position.

For the purpose of this Quick Tip, there are two types of polarizing filters – linear and circular.  A circular polarizing (CP) filter is for use with all cameras with beam splitters in the light paths of their TTL exposure meter and with autofocus lenses. A Linear polarization filter is for SLRs and rangefinder cameras without beam splitters in their light paths.  Circular polarization has the same pictorial effect as linear polarization, but allows for proper exposure metering and/or autofocus distance settings. Since most of us today use DSLRs (digital single lens reflex cameras), for this Quick Tip I will focus on the CP filter which is a tad more expensive, but is more universal in use than the linear filter.

The CP filter, which consists of two parts, is used by rotating one part of filter to absorb polarized light perpendicular to the lens as other part remains fixed.  Remember that the subject that you are shooting will display maximum  polarization at right angles to the sun’s position.  When the filter is rotated by 90º from its normal reflection-reducing position, it can even appear to increase the relative intensity of reflections on water, glass, lacquer and plastic materials up to a factor of 2.  At 180 degrees, with the sun right behind you, polarization is almost non-existent and the filter will not yield the same results.

White-spotted jellyfish

As previously mentioned, one of the most common uses of the CP filter is to  increase the saturation of the true color and create dramatic deep blue skies with bright contrasting clouds.  Another common use is to control reflections.

Both of these effects can often be seen when using polarized sun glasses.  When wearing polarized sunglasses, as you look at the sky and tilt your head, you will notice how the sky pops at certain angles – this happens when you are perpendicular to the polarized light. If you look at certain surfaces (that are reflecting polarized light) you will notice that the reflections can be removed depending on how you position your sunglasses.

As seem to the left, CP filters cane be very used with great success when shooting through aquarium glass.  The CP filter, by helping to reduce reflections from the glass, will make your photographs of marine life look clearer and their colors more saturated.

CP filters are not just for color photography.  In Black and White photography, CP filters can greatly increase the contrast and make white clouds stand out dramatically from an intensely darken sky.

There are a few things to consider when using a CP filter:

Filter Thickness and Vignetting

Since CP filters consist of two parts, one of which must be rotated, the combination can tend to be thick.  The added thickness of the frames to the edge of a wide-angle lens may cause vignetting.   The wider the coverage of the lens, the more noticeable the vignette.  When using a wide-angle lens, it is important to purchase ‘thin’ CP filters which are specially designed for that purpose.  I tend to purchase the thinnest filter, (that is threaded on both ends), that is available.

Wide-Angle Lenses

In addition to possible vignette, there is also the issue that parts of the sky that are not at a 90-degree to the sun will react differently to the polarizer.  The end result can be a most unnatural graduation of color. It is important to keep this in mind when you have a wide-angle lens on your camera.

Installation / Removal

Many folks will have added a UV filter for protection attached to their lens – and then attach the CP filter on top of that.  Not only will this add to the vignette effect but by adding yet another layer of glass between you and the subject can cause ‘ghosting’ (light reflections) and somewhat degraded image quality.  But for some, it may also introduce a challenge in separating the CP filter from the UV filter – remember part of the CP filter rotates.  It is suggested to remove any existing filters and use the CP filter alone.  There is no need to have UV filter plus a CP filter at the same time.

Loss of light

A CP filter reduces incoming light by an average of 1.5 stops.  Although not a deal breaker, this needs to be taken into consideration when making your exposures.

Quality

As with all filters, since I am adding another element between my lens and the subject, I do not want to degrade my image in any way.  For this reason, I always go with higher quality filters, such as from B+W, Cokin and Hoya.  Many pro lenses (f/2.8) use the same size 77mm filters – which can save you quite a bit by not needing to have multiple CP filters.  The better quality CP filters cost  $100 – $300 and often have special coatings to enhance the transmission of light, be designed to reduce internal reflections, be harder than regular glass and be threaded on the end to accept lens caps.  And, yes – you do pay for those features.

For me, if I invest over $1000 in a quality lens, I am certainly not going to put a low-cost filter between it and the subject. And, since the filter will fit multiple lenses, the extra investment can be worth it in the long run.  Sometimes you do get what you pay for (but do shop around for the best deal).

Now for the opening shot.  The location was the lily ponds at Longwood Gardens in Pennsylvania.  These ponds have wonderful water lilies floating in ink-black water that helps offset their beauty.

As always – I planned my shot. Where possible, I walk around and look for the best angles to bring out the subject. I look for lighting angles, background distractions and the overall composition before I take that first shot.  Yes, I am the guy that walks around making a rectangle with his fingers like a viewfinder.

For this shot, as you can imagine from my discussion above, I used a CP filter.  I positioned myself at an angle so that as I turned the CP filter I was able to ‘fine tune’  just the reflections I wanted to capture.

I ‘spot metered’ on the brightest part of the plant to avoid clipping (burning out white areas) and wanted to take advantage of the wonderful natural light. I took several test shots and reviewed my histograms for proper exposure. (White spikes to the right of the histogram meant parts of the image would be burned out with no detail.) I also shot RAW so I could make any fine EV adjustments in Post Processing if necessary.

Lastly I waited for a breeze to create ripples in the water to add a touch of texture. And that’s it.  What you see is what I saw.  It is the photographer’s desire to capture the shot correctly in the camera rather than to use a lot of Post Processing tricks.  [The camera was a Nikon D700 with 70-200 f/2.8 lens@200mm.  Settings: ISO 200, 1/640, f/5.6.  Tripod mounted using a manual trigger release.]

Polarizing filters can be used in a number of situations – have fun and see how one can improve your shots. 

All shots were taken with a Nikon D700 or D800 using a 70-200 f/2.8 or 24-70 f/2.8 and Schnieder Optics  B+W  77mm XS-Pro Digital MRC Nano Kaesemman CP Filter. All shots are taken from myImagez.com.