Tag Archives: neutral density

Bracketing vs. Graduated ND Filters

Cocoa Beach Pier, Technique, , ,

I’d long ago answered this question, but a comment from Frank B. about this image caused me to reconsider some things.

Cocoa Beach Pier before dawnCocoa Beach Pier before dawn

Fair warning:  This post is a little deep into the weeds.  Feel free to look at the photo and move on if it isn’t your thing.  But I think it’s an appropriate subject, since part of the blog’s purpose is “… and how to photograph them.”

What are we talking about?

Bracketing means taking multiple photos of a scene, each with different camera settings (see this Wikipedia entry).  In this case, I made three photos at different exposures so I could capture the entire dynamic range from super dark under the pier to super bright above the clouds.  Making just a single exposure would’ve risked losing detail in the shadows or highlights (or both).

You can also use a Graduated Neutral Density Filter (GND) – an optical filter you add in front of your lens to reduce light in the bright part of the frame (see this Wikipedia entry).  Typically they have a 2 or 3 stop reduction that transitions into clear.

I’d long ago experimented with GNDs and decided not to use them.  I can  mostly reproduce their effect in static scenes by bracketing and then blending the resulting frames in post-processing.  For landscape images bracketing is an easier solution in the field and gives me more control and a better final result.  You can read about one example of my technique in this post (from back in 2011).

But then … Frank left a comment:

… amazing how the clouds remain sharp compared to the water given the time of exposure

And my reply:

Frank, this is a 3 frame, hi-res exposure bracket hand blended in Photoshop. The bottom portion was at f/5 for 25 seconds. The top was at f/5 for 3.2 seconds. So that and distance is why the clouds are sharp compared to the water.

The way I made this image resulted in a huge difference in shutter speed between the water at the bottom and the clouds at the top.  And using the Olympus Hi-Res mode exaggerated the shutter speed differences since it combines 8 separate captures to create each hi-res output file.

If I’d used a GND the shutter speed would be constant throughout the frame and the blur in the clouds would’ve matched the blur in the water.  In this particular case,  bracketing exposure by varying aperture instead of shutter speed would also make the motion blur consistent.  I’ve never done that since it seemed like it would lead to other issues (inconsistent focus / depth of field).  It’s something to think about and maybe try in the future for a setting where consistent motion blur is important.

Thanks for the question Frank!  Photography is fascinating.  There is so much to think about and still left to learn.

And thanks to everyone else for stopping by and reading my blog (especially if you read all the way through!). Now – go make some photos!

©2019, Ed Rosack. All rights reserved

Long Exposure with Variable Neutral Density Filters

Cocoa, Technique, , , , ,

A friend wants to make long exposure photos on an upcoming trip. I recommended using a Variable Neutral Density Filter (VND) and offered to let them try mine.  So  we headed over to the Cocoa Beach Pier last Friday to test them out on some ocean waves.

Cruising homeCruising home. VND, ƒ/11, 35 mm, 0.3sec, ISO 100

VNDs are made from two polarizing filters – one’s fixed and the other rotates. You use the rotating one to vary the amount of light that’s blocked (typically between 1 or 2 and 6 or 8 stops).  I like them because they give you precise and easy control over how much light hits your sensor.  If you reduce light on the sensor, you can use a slower shutter speed or a wider aperture for a given scene.  They’re good to have when you photograph waterfalls (slow shutter to blur / smooth water) or in bright light (to shoot with a wider aperture and blur backgrounds).

Here’s my approach for smoothing water:

  1. Mount the camera on a tripod and trigger it with a remote or the self timer.
  2. Set ISO (usually for best quality). Don’t use auto ISO.  We want the  camera to vary shutter speed instead of changing ISO when the VND rotates.
  3. I use Aperture Priority mode and select the F-stop (for depth of field, image quality etc.).
  4. Compose with the VND filter at its minimum value (brightest setting).
  5. In bright light, you can use auto focus.  In dim light, you may need to  manual focus so the camera’s auto focus doesn’t hunt when you  darken the VND.
  6. Now, slowly turn / darken the VND until your shutter speed reaches the value you want.  You’ll need to experiment to find what looks best to you, but for water try between .25 and 1 second.
  7. If you can’t get a slow enough shutter, you can close down your aperture, or lower your ISO.

Some things to watch out for:

  • Like much in photography (and life!), you can find very expensive VNDs and very cheap ones. I’ve had good luck with name brand ones in the middle price range.  Don’t buy the cheap ones!  They may not be optically flat or coated, and might introduce color shift problems.  You’ll probably pay more for thinner ones too, which will reduce chances of vignetting.
  • Definitely look for VNDs with coatings to help prevent reflections / flare.  You’re adding four more air/glass interfaces to the front of your lens and you can’t use a lens hood, so coatings will improve performance.
  • Since these filters can be expensive, I recommend buying only one, sized to fit the biggest diameter lens you’ll use it with.  I have a 77mm VND and step down rings to mount it on my smaller lenses.
  • Some VNDs can be rotated too far and will show an ugly cross-shaped anomaly.  If yours does this, watch for it and back off until it disappears.  Some are made with a stop so you can’t rotate them too far.
  • Check your results as you go.  It’s easy to over expose highlights in moving water, so you may need to dial in some negative exposure composition.  Also, if the light getting through is too dim, your camera’s meter may not work well.  In that case you’ll have to change to manual exposure and adjust accordingly.
  • Make several exposures at different shutter speeds so you’ll have distinct looks to choose from when you get home.

Golden beachGolden beach. VND, ƒ/8.0, 26 mm eq., 0.8sec, ISO 200

That’s it – simple, right?  Do you use VNDs?  If so, let me know where I can view your long exposure photos.  And if you have any hints of your own, please share in a comment for everyone.

You can click on these images to see a larger version on Flickr. Thanks for stopping by and reading my blog. Now – go make some photos!

©2019, Ed Rosack. All rights reserved