Graduated Neutral Density (GND) filters are a landscape photographer’s best friend.  They are absolutely necessary.  If you have not used them, GND filters will be scary at first and hard to understand.  Do not be intimidated.  Use them.  Learn them.  Your photos will be greatly improved.  Trust me.

Lee, a photographic filter company, has a fantastic website (www.leefilters.com) which explains and demonstrates many of its filter products.  I highly recommend you visit this site.  Read everything and watch all the videos.

You’ve seen the problem before when you expose for a subject in a dark foreground and there’s a bright sky in the background.  Your subject will be properly exposed, but your background will be grossly overexposed, or “blown out”.  Had you exposed on the sky, your result would have been exactly opposite, i.e., sky properly exposed and your subject grossly underexposed.

Within reasonable bounds, the human eye does not have this problem.  You can look at the scene just described and see a properly exposed subject and a properly exposed sky – your camera sensor cannot.  This is where the GND filter comes in.

The GND filter will help reduce the light-to-dark difference of a photo and thereby bring it to within the working contrast range of your camera’s sensor.

A very common application is the dark foreground and bright sky conditions mentioned above.  A GND filter will be positioned in front of your lens such that it will reduce the brightness of the sky just enough to bring the bright to dark difference of the photo to within the range of your sensor.  Eureka!  No more bright blow outs.

This is demonstrated with the following photos.

Similar to ND filters, GND filters come in varying strengths, e.g., 1 stop, 2-stop, 3-stop, etc.  There are partial stops too just like ND filters.  And as you would think, you will use a higher strength filter for larger light-to-dark differences.

There are two ways to determine what strength of GND filter to use, 1) trial and error, and 2) calculation.  For the calculation method, spot meter a point in the foreground and repeat the same for the background.  Subtract the two exposures and the difference is the GND filter strength.  Place this filter on the lens and let the camera expose on the foreground spot.  The result should be good, but check your replay and histogram.

Here’s an example to demonstrate this technique.  You are shooting a seascape where your camera says the foreground exposure is f/13 at 1/60 sec, and the background exposure is f/13 at 1/500 sec.  Subtract the number of f/stops between these two exposures.  You have used Aperture Priority so all you need to worry about is shutter speed.  Easy.  Half of 1/500 s is 1/250 s, half of 1/250 s is 1/125 s, and half of 1/125 s is 1/60 s.  The difference is therefore three whole f/stops, and you will use a 3-stop GND filter.

If you’ve investigated Lee’s website, you’ll see that in addition to varying strength, there are also “hard” and “soft” edge GND filters.  These are shown below.

The hard edge filter is used when the light-to-dark difference is straight and well defined – such as in our example above.  The soft edge filter is used in all other applications, i.e., light-to-dark difference is not straight and not well defined.  We’ve included an example application of a soft edge filter below.

Show a non-straight and poorly defined light-to-dark example photo.  Then show placement of a soft edge GND filter.  Show at an angle.

You’ll see in the example above that the GND filter has been rotated to better fit the light-to-dark difference.

So far okay, right?  Well, don’t get too over confident.  We haven’t addressed the hard part yet – proper placement of the GND filter.  All your efforts and good intentions will be wasted if you have not properly positioned the GND filter.  As a matter of fact, a poorly placed GND filter cannot even be partially good.  It will always be bad.  See the two examples below.

Show two photos, one GND too high and one too low.

Large aperture

DOF button

Can we show an example?