Using Neutral Density Filters

Pond Brook Falls 67seconds, 6 Stop ND

   

10 Stop ND

It is a common saying that, “To a man with a hammer everything looks like a nail”.  Over the last few days, everything has looked like an opportunity to use my new Neutral Density Filters and I have been having a great time. 

Over the years I have used various filters when I wanted to reduce the light reaching my camera’s sensor.  Most often this has been when I was trying to slow my exposure of flowing water to get that soft, cotton candy look, which I love.  I routinely use my polarizer which, with the right direction of light can knock of one or two stops as well as cutting the reflections on the rocks.  With low light, a

Chesterfiled Gorge Cascade, 79 Seconds

polarizer may be all I need to get the exposure down to 0.5 to one second, which creates a nice soft look without obscuring all the detail in the water.  If I need to block more light, my next step has been to use my gradient neutral density filters.  I have a nice set of Cokin filters, which are designed to block the light in a portion of the scene.  Most commonly this is helpful to reduce the contrast between a bright sky and a foreground which is shadow, but the portion of the filter which has the maximum darkening effect is usually large enough to cover the entire lens.  It is an awkward arrangement but, in a pinch, it can work like a fixed neutral density filter.

These have been my light reduction work-arounds, they can work but are difficult and, despite my best efforts, at most I can reduce the light by 3-5 stops, not the 6 – 10 stops that can really change a scene.  Obviously, I needed a set of fixed ND filters that would be easy to use and provide a wide range of light reduction options.  Oh, and they need to be high quality and low price.  Easy.

Ashuelot Falls 46 Seconds, 6 stop ND

Finding a Reason to Stop at 2Filter.com

That brings us to earlier this week.  Susan and I were heading home from a tour of possible wedding party venues for my daughter (YEH), and happened to be passing the unobtrusive offices of 2Filter.com in Gilsum New Hampshire.  2Filter.com is a great on-Line source for photographic filters, but it is not a retail store.  The first time I made an order, I scared the hell out of the people in the office when, upon being asked for my shipping address, I announced that I would be dropping by to pick it up.  Since then I have enjoyed a friendly relationship with the owner and his helpful staff.  On this day, I had to come up with a reason to stop at the office and ND filters came immediately to mind.  With the help of the staff,  I came away with a set of Fixed NDs [3,6 and 10 stops), and also a Clear-Night Filter for my astrophotography. 

Ashuelot River Park, 45 Second 10 Stop ND

When buying filters, you want to get multicoated glass filters with thin but sturdy rings.  The thin rings are important to avoid vignetting especially if the filters are stacked.  My kit of Haida fixed ND filters met my criterion and for a fair price.  It was then time to go out and play.

So what situations call for the significant reduction of light making it to your sensor?

1)   Flowing Water

Pond Brook Cascade
1/60th second Polarizer

The use of long exposures to make flowing water appear like a gossamer veil is one of the most commonly used pieces of photographic magic.  Water never actually looks like cotton candy, but it is just one way to capture the feel of waterfalls and streams.  Different slow shutter speeds create different renderings, but on bright days, even with a polarizing filter, it can be difficult to slow the shutter sufficiently.  Neutral density filters allow long exposure even in the brightest sunlight.

60 Seconds, 6 stop ND

 For waterfalls, I typically use shutter speeds from 0.5 to one second, but I have been having fun experimenting with my new NDs for much longer exposures. My camera only goes to exposures of 30 seconds, but with the bulb setting I have captured my flowing water up to a minute or more.  Definitely a different look and feel.

2)   Moving Clouds

Chesterfield Town Hall

Technically just another kind of flowing water, using ND filters to capture moving clouds can lead to interesting effects.  The optimal shutter speed depends on the density of the clouds, how fast they are moving across the sky and, of course, personal preference.  I am excited about getting the chance to experiment with angry, fast moving clouds, but, as of this writing the weather has been too damn nice.  Over this weekend I caught puffy clouds flying by ther Chesterfield Town Hall.

71 Seconds, 10 Stop ND

3)   Video Shutter Control

It is generally understood that video has a more natural, “cinematic” appearance with a shutter speed  of 1/50^th – 1/60^th of a second, which is roughly twice the usual frame rate.  This can be difficult to achieve when filming on bright days, and neutral density filters are routinely used to block the light sufficiently to allow the optimal shutter.

4)   Bright Light Shallow Depth of Field, Especially Portraiture

Portraits are always difficult on sunny days.  The stark shadows, the squinting and the flat colors often present insurmountable challenges.  Reflectors and fill flash can help, but the bright light may also make it impossible to open the aperture sufficiently to get a nice soft focused Bokeh behind your subject.   Many of the newer DSLRs have faster shutter speeds that may be used to avoid this problem, but cutting the light with an ND can also permits a wider aperture.

5)   Long Exposure Crowd Control

Portland Alley

   Over the years I have occasionally been able to use long exposures to remove unwanted people or vehicles from a scene.  With a long shutter moving subjects may not be in one spot long enough to register on the sensor.  

30 Second Exposure

  A few years ago, I used this technique on a night shot of a busy alley in Portland Maine.  A 30 second exposure was long enough to remove all but the idle smokers from the scene.  For the dark alley, all needed was f/22 and an ISO of 100 to allow the 30 second exposure, but for shots in brighter light a neutral density filter would be needed. 

Maine Street Keene, NH

Earlier this week I set up on Keene’s busy Maine street in bright midday sunshine.  Traffic was heavy, but I magically removed most of the cars a 10 stop ND, f/22 and an 8 minute exposure.  I couldn’t remove all the evidence of bright car lights.  This technique will work better when used to remove people (who don’t have headlights) strolling by, and when the motion is perpendicular to the cameras view.

8 Minutes, 10 Stop ND

Neutral Density Lessons

These are just a few uses for fixed Neutral Density Filters.  I am sure more can be suggested.  I have only been playing with my NDs for a couple of weeks and can hardly be considered an expert in their use, but I have learned a few things from my experiences so far.

Stacking

First NDs can be stacked either with themselves or with other filters.  When NDs are stacked there is a wide range of effects than can be achieved. A 3 stop and a 10 stop can be stacked to reduce exposure by 13 stops.  Although it would be unlikely to be necessary, stacking all three filters from my new kit, I could reduce the light by 19 stops!  With that I could hit the shutter and come back in several days to review the results. 

Stickney Falls, Dummerston Vt, 93 Seconds

For my waterfall pictures I like to use a polarizer to reduce the reflections off the rocks and a polarizer can be stacked with an ND.  The polarizer reduces the exposure by an additional stop or two.  With more powerful NDs which essentially eliminate the light,  I must adjust the polarizer as well as the composition and focus before I add the ND.  Care needs to be taken to avoid moving the Polarizer ring as the ND filter is screwed in place.

The other important issue with stacking any filters is to watch for vignetting.  This is more of a problem when thick filter rings are stacked and when using wider angle lenses. 

Focusing and Composing

63 seconds, Chesterfield Gorge

Even with relatively weak ND filters, it can be difficult to compose and focus in the viewfinder.  One approach is to focus before the filter is added, but I found that even with moderate amounts of light reduction, I could use Live View to focus and to adjust the effects of a polarizer on the LCD.  With the 10 stop filter, everything was completely black and I had to make my adjustments before adding the filter.  Of course, cameras vary, and experimentation will usually be necessary.

Exposure

Maintaining the same exposure after adding a ND filter is simply a mater of compensating for the number of stops.  Since aperture adjustments are limited, I tend to keep the f-stop fixed and compensate with changes in the shutter speed, but it can get confusing when trying to count out ten stops on the shutter adjustment. 

Happily, there are several easy Apps, available in the iTunes App Store, that make this adjustment easy.  I settled on free one (typical) called the “Long Exposure Calculator”.   You start by finding the correct exposure without the ND.  For my waterfall pictures, this means the correct exposure with the polarizer in place.  This “Base Shutter Speed” is entered into the App and, when the filter density is dialed in, the correct filtered shutter speed appears on the bottom.  Simple, and if the shutter is greater than 30 seconds, a timer pops up to count down the appropriate amount of time. This works great, but if the light changes some adjustment may be required.

Long Exposure Calculator

I’ve been having great fun with my NDs.  One of the remarkable things about photography is how even relatively inexpensive pieces of kit can open exciting new ways of seeing our world.  Go have some fun.

Evening Stickney Brook Falls, Dummerston Vt : 60 sec 6 Stop ND