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.
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:
- Mount the camera on a tripod and trigger it with a remote or the self timer.
- 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.
- I use Aperture Priority mode and select the F-stop (for depth of field, image quality etc.).
- Compose with the VND filter at its minimum value (brightest setting).
- 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.
- 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.
- 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.
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