“ND” refers to “Neutral Density” filters. These are varying densities of gray, designed to block varying amounts of light in order to have long exposures during the daylight. Normally, having an exposure time of 4 seconds or so would just give you a blank white image; that amount of time in sunlight would just saturate the camera’s CCD. ND filters are designed to counter that.
The two most prevalent types of images taken with ND filters are those of running, foaming water (it gives the water a misty, dream-like look) and public attractions like monuments (long exposures mean that the people milling around never stay in one place long enough to register on the image).
You can find an excellent article on using ND filters here. That same article also discusses a different way to get the same result–by using two polarizing filters, a circular one attached to the lens, and a linear one attached to that filter. That gives one a bit more flexibility than a standard ND filter, which is usually a single strength.
So having read the article, I decided to try my hand at it. My camera is a Nikon D70, and my lens is a Quantaray 18-200 zoom. The filters are Kenko (linear) and Promaster (circular). Of course, all of the shots below were taken using a tripod. I couldn’t think of any local monuments, and I also couldn’t remember any areas with interesting running water, but I chose the latter nonetheless. None of the shots below have been enhanced in any way.
The above was taken with the camera on Auto. Exposure 1/125, F/5.6. Below is the same area, also at F/5.6 but with an exposure time of 4 seconds.
In addition to making bubbly water mist-like, it can also smooth water surfaces. Below, an “Auto” shot at F/5.6 and 1/125.
The same shot (slightly reframed, mostly via zoom) at 4 seconds, and F/32.
The reason for the reframing was (I think) something to do with the angle of the light. Because when I tried to do the ND shot with the original framing (20 seconds at F/11) I got this–
–which is, in its own way, quite lovely but not really what I wanted. Even messing with it in PhotoShop* didn’t really get me what I wanted.
So, it’s definitely not an exact science. Which is one of the nice things about digital cameras–mistakes don’t cost you anything, and in fact are a good learning experience.
A few more examples below.
6 seconds at F/9:
20 seconds at F/16:
20 seconds at F/18 (slightly tweaked in PhotoShop for exposure):
15 seconds at F/20:
Now, to find some waterfalls…
Thank you as always for stopping by.
*The folks referenced in the link above make a really nice image editor called Zoner Photo Studio. It has a lot of the same functionality as PhotoShop but is a lot less expensive. It’s well worth checking out; alas, I’m pretty well wedded to PhotoShop for the foreseeable future…but I do have a copy of Zoner. Who knows what might happen in the future?