Archive for the ‘CPL’ Tag

Friday Foto Talk – Using a Circular Polarizer, Part III   11 comments

Lizard tracks from the previous night in Death Valley, California.

This is the final of three parts on the circular polarizer.  In Part II we looked at how you can use the filter in order to maximize its benefits while handling most of its drawbacks.  There is more of that kind of advice in this post, along with some practical tips that apply to any screw-on filter.

EFFECTS OF A CPL & HOW TO HANDLE THEM

  • A circular polarizer appears to change the colors in some images.  Mostly it’s the blues you’ll notice, but it can also saturate and brighten the warm tones.  A good CPL will not cause much of a color shift per se.  It’s more of an apparent effect and doesn’t happen in all images.  But in any case if you’re shooting RAW it’s easy to warm (or cool) things a bit using the white balance sliders in your editing program.  You can also get a polarizer with built-in warming.
Dramatic skies plus a polarizer make for a nice chance to shoot from a low point of view in the Nevada desert.

Dramatic skies plus a polarizer make for a nice chance to shoot from a low point of view in the Nevada desert.

  • You may end up with uneven-looking blues in the sky when using a polarizer.  It’s one of the main problems I run into when shooting landscapes with this filter.  Patches of darker and paler blues, while they do occur naturally in parts of the sky, can be exaggerated with a CPL, making things look unnatural.  If you’re using a wide-angle lens this effect is pretty obvious and hard to avoid.  All you can do is rotate the CPL less and/or change composition.  Try pointing the lens at a different angle to the sun and include less sky overall.  If you’re using a lens with a longer focal length, pointing at right angles to the sun should give you an even effect no matter how much you rotate the CPL.
In this shot at Great Sand Dunes, Colorado, you can see the obvious effect in the sky from using a CPL.

In this shot at Great Sand Dunes, Colorado, you can see the obvious effect in the sky from using a CPL with a wide-angle lens (18 mm.).  It’s a hard thing to correct on the computer.

  • Although a CPL often amps up your colors just the right amount, it can also hinder natural color saturation in some instances.  For example, I’ve found in frontlight (sun is behind you shining on the subject), and with fall colors, using a polarizer will often take away a little vibrance.  If it’s cloudy and the leaves are wet it may do the opposite, blocking reflections and allowing colors to come through as described in Part II.  But be careful about using the CPL when shooting colorful subjects, especially in frontlight.
The Colorado Rockies.

The Colorado Rockies.

AVOIDING MARRIAGE BETWEEN LENS & FILTER

  • Last but not least, let’s not forget about your threads.  No, I’m not talking about clothes!  It’s quite easy to tighten the filter too much on your lens.  Then you can’t get it back off!  A CPL is worse than other filters because you’re always rotating the filter element to adjust it, maybe tightening it even more.

 

  • Prevention is the key.  Getting a good filter with brass instead of aluminum threads will help.  And of course, try not to tighten it too much.  When you rotate the outer ring to adjust filter strength, occasionally go the opposite way (left).  Just don’t do this much or you may rotate the filter right off your lens and drop it.  Mostly rotate the same way you screw the filter on, to the right.
I avoided using a CPL here because it wouldn't do much except increase the possibility of flaring.

I avoided using a CPL on this blooming desert gold in Death Valley because it wouldn’t do much except increase the possibility of flaring.

  •  More prevention:  Keep your filter clean and lubricate.   Use a hand-blower to get rid of little pieces of grit that try to get in between the rings.  Also, occasionally lube the filter threads with silicone spray.  Go outside away from your gear and spray the silicone into a small cup or bottle cap.  Then use a Q-tip to carefully apply the lube to the threads and along the seam where the CPL rotates, avoiding the glass.  Don’t use too much!  Then screw the filter on and off your lens, rotating it back and forth a few times to spread the silicone evenly.

 

  • If you get a filter stuck you can try a couple things.  One or two fat rubber bands, like the kind on broccoli at the grocery, allow you to better grip the filter and perhaps the lens.  Try not to pinch.  Spread your fingers and use even pressure all around the filter.  If a filter is really stuck, try this:  Get some of that tacky rubber material made for lining drawers & shelves.  Cut a couple flat squares and on a table lay your filter flat on one of the squares.  Spread the other square flat and tightly onto the filter’s outer ring.  Using your palm or fingers evenly spaced around the rim, gently and evenly press down while twisting to the left.

Thanks for reading.  Enjoy your weekend!

No polarizer required for this image of the desert mountains near Beatty, Nevada.

No polarizer was necessary for this image of desert mountains near Beatty, Nevada.

Friday Foto Talk: Using a Circular Polarizer, Part II   11 comments

Recently-flooded wash in Death Valley, California.

Recently-flooded wash in Death Valley, California.

Last week I got all technical about how circular polarizers (CPLs) work.  Of course you don’t necessarily need to know all that to shoot with them.  But it certainly doesn’t hurt.  The more you know about how CPLs work the better able you are to extend the situations in which you use them.  You can more competently go beyond landscape photography, which is where they’re primarily used (and where I’ll focus this tutorial).

Now let’s get into the meat of things and learn how to employ these great filters in your photography.  As usual it’s a good news/bad news story.  We’ll start with the bad.

Staying in Death Valley, this dramatic side-light didn't really need a CPL.  I used one but dialed down the strength a bit.

Staying in Death Valley, this dramatic side-light didn’t really need a CPL. I used one but dialed down the strength a bit.

DOWNSIDES & HOW TO MINIMIZE THEM

  • First off, it’s a filter, the kind you screw on to the end of the lens.  This adds another layer of glass between your subject and your sensor or film.  That introduces a chance for flaws in the way light is transmitted, at least in theory.

 

  • But as long as the filter isn’t cheap and you keep it fairly clean, it should yield perfectly sharp images just as when you’re not using a filter.  I’m not the type of photographer who puts a lot of stock in the idea of an imperfect image.  If I can’t detect any fall-off in quality then it’s simple: the benefits of using the filter outweigh any theoretical considerations.

Arches National Park, Utah. I used a CPL, maximizing “punch”, mostly in the sky.

  • Again because it’s a filter, a CPL will increase the possibility of flaring: those often annoying but sometimes interesting bright colorful spots that show up in your pictures when you shoot toward a strong light source like the sun.  But you can control flares by keeping your filter and lens clean, by using a hood, and of course by not pointing directly toward the light source.

 

  • Sometimes you have no choice, your photo demands pointing it toward the sun.  Then you simply roll the dice and keep shooting until you get flares that are easy enough to remove on the computer.
Washington's Olympic Peninsula at Lake Quinalt. These are the kinds of flares that aren't too hard to clone out on the computer.

Washington’s Olympic Peninsula at Lake Quinalt. These are the kinds of flares that aren’t too hard to clone out on the computer.

UPSIDES & HOW TO MAXIMIZE THEM

  • So you know a CPL filter reduces reflections.  But this may or may not be what you want.  In the case of mountains reflected in a lake, you’ll want to be careful to rotate it just the right amount to maximize the color and light in your reflection.  If you rotate it fully you’ll begin to see what is underneath the water, if it’s shallow enough.  In the case of wet rocks or plants, you may want to use it fully to help bring out the color of the rocks or greenery.
For this hot spring, I wanted to see the subtle colors of the algae growing along the little falls, plus I wanted smooth water. Cutting reflections and lengthening exposures is a great two for one when using a CPL.

For this hot spring, I wanted to see the subtle colors of the algae growing along the little falls, plus I wanted smooth water. Cutting reflections and lengthening exposures is a great two for one when using a CPL.

 

  • A CPL also reduces the total amount of light reaching your lens.  Some models reduce the light only slightly (called “high-transmission” CPLs), but most block between one and two stops of light.  In a way this is a downside because it can hurt you when you’re hand-holding the camera and need a fast shutter speed.  You may need to raise ISO.  But it can help too.  For example when you’re on a tripod and want to lengthen shutter speed, say to blur a waterfall (see above photo), a CPL can provide just the right light-blocking strength.

 

 

Without a circular polarizer.

Without a circular polarizer.

  • A circular polarizer will darken and tend to saturate colors a little, especially the blues in a sky.  When there are white clouds it increases the contrast between blue sky and cloud, quite a lot if you’re shooting at a right angle to the sun.  A typical landscape shot with a CPL has more “punch”, or mid-tone contrast.  The photos above and below, which are deliberately sort of “average”, show the difference.
Same scene as above with a CPL.

Same scene as above with a CPL.

  • As the pair of shots above show, a CPL can do nice things for colors, especially when you consider that when shooting RAW your images often come out looking flatter and more washed out than the real scene was.  But as you can also see, contrast is increased over the RAW image as well.  That’s why a CPL can often be used to great effect when you’re shooting for black and white.  Try it.

 

A polarizer can lend black and white images a little more drama: Panamint Valley dune field, Death Valley N.P., California.

Okay that’s it for now.  Next time we’ll conclude with more guidance on using CPLs, along with tips on maintaining them.  Happy weekend everyone!

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Friday Foto Talk: Using a Circular Polarizer, Part I   2 comments

Soap-tree yucca growing on the dunes of White Sands National Monument, New Mexico glow in the bright morning sun

The circular polarizer (or CPL) is a must-have for any landscape photographer.  This handy filter can be used in many different situations, but like any piece of photo gear it helps greatly to know exactly what it does and what its benefits and downsides are.  This is the first of two parts.

WHAT A CPL IS & HOW TO USE IT

  • A circular polarizer is a filter that screws on to the threaded front end of your lens.  It has two pieces of glass sandwiched together.  So it also has two rings for you to grip.  If you grip the ring closest to the threads you will be able to screw the filter on and back off your lens.
  • Once it’s on (not too tight!), grasp the ring furthest from the threads to rotate the front piece of glass relative to the other (now fixed in place).  This is the way you adjust the filter’s strength.  It goes from minimum to maximum effect with 90 degrees of rotation, then back to minimum if you continue rotating all the way to 180 degrees.
I used a polarizer for this shot in Death Valley recently because I wanted to maximize the effects of the side-light and show the texture in the land.

I used a polarizer for this shot in Death Valley recently because I wanted to maximize the effects of side-light to show the texture in this awesome alluvial fan, visible in the lower part of the image.

HOW A CPL WORKS

  • The CPL filter works by polarizing light in a couple different ways.  When light is reflected it becomes polarized to one degree or another.  Light rays can be thought of as vibrating waves.  When emitted by some source (like the sun), the light waves vibrate in all directions.  When light hits a reflective surface and bounces off it, the waves vibrate mostly in one direction, parallel to the reflecting surface.  The light has become linearly (or plane-) polarized.

 

 

Light reflected from a lake becomes polarized.

Light reflected from a lake becomes polarized.

 

  • A circular polarizer works by first polarizing the light linearly, then turning it into circularly polarized light.  In the case of the plane-polarized reflected light above, the front glass element of the CPL acts as if it has slits, either allowing the polarized rays through or (partly or fully) blocking them.
  • The rear glass element, the 2nd one the light passes through, takes that linearly polarized light and polarizes it further, but this time circularly.  If you think of the linearly polarized light as a line on a graph, with both horizontal and vertical (X and Y) components, the CPL is blocking one component (vertical, for example) more than the other.  It turns it into a vibrating wave that sort of spirals.  The light that finally reaches your lens is now circularly polarized!

 

Diagram of a circular polarizer in action. Click on image to go to source website.

Diagram of a circular polarizer in action. Click on image to go to source website.

  • As described above, you adjust a CPL by rotating the front glass element.  This increases or decreases the degree of circular polarization.  And if you have reflected light, off a lake or river for example, rotating the filter also changes how much of that plane-polarized light you’re blocking.  Again, think of that front glass element as having ‘slits’, which when crossed at an angle to reflected light will prevent some of that naturally polarized light from getting through.

Yellowstone’s Lone Star geyser erupts.

  • By the way, that crossing of the slits to plane-polarized light is called cross-polarization, and it’s how polarized sunglasses work.  Their “slits” are fixed in a vertical position, enabling them to block the plane-polarized light reflected off of water, roadways and other horizontal surfaces.  Look at the reflection off a vertical store window  with your sunglasses on and you’ll see they allow that light right on through.

I used a polarizing filter at this pool in Ash Meadows Wildlife Refuge, Nevada in order to show some of the detail under the water.

BASIC FIELD USE

  • Again the effect increases as you rotate the moveable (outer) ring.  In the case of light reflected off water or glass, rotating the filter to its max. position (90 degrees from minimum) will cut the reflection dramatically.
  • And for similar reasons, as you point the camera close to right angles (90 degrees) with the sun or other light source, the polarization effect increase dramatically as you rotate the filter to its max. position.

Those are just the two basic ways to use a circular polarizer in the field.  There are quite a number of other, more subtle ways to use a CPL in photography.  And next time we’ll look at using the filter to improve your images, all the while emphasizing its strengths and dodging the inevitable drawbacks.  Have a great weekend and happy shooting!

The barren, channeled nature of a Death Valley alluvial fan is highlighted by strong side-light. I used a CPL but not set to its max setting.

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