How properly expose a long exposure in daylight?

Question

I was shooting some lake waves with some nice color in them, and I wanted to do a long exposure to smooth out the wave and color, similar to the effect you see from a long exposure of whitewater or a waterfall.

However, the image was way too overexposed, even at 1/2 a second (f/20, 100 ISO):

I went to the camera store and asked them. The guy at the offered two solutions:

1. Shoot an HDR shot, either in camera, or compose one in photoshop.
2. Get a variable nuetral density filter.

However I wonder, is there a way to make a very small aperture in a lens-cap, ala a poor-man's pinhole camera, that would reduce light sufficiently to properly expose a very long timelapse?

Are there other methods available?

Answer 1

You are spot on! Use a sewing needle heated in a candle flame and carefully pierce the lens cap. Make a trial exposure and enlarge the hole if needed. Keep in mind that a tiny pinhole will induce diffraction that degrades. Also, a pinhole has super depth-of-field. Anyway, experimentation leads to discovery.

Answer 2

Some techniques to take "long" exposure shots:

1. Neutral density filters. Good neutral density filters tend to be priced consistently with other good photographic equipment. Inexpensive neutral density filters may or may not provide satisfactory results.

2. Wait for the light to change to lower intensity around dusk. Soonest predictable change in the light, but potentially a short shooting window.

3. Get up early and use the lower intensity light around dawn. Another reasonable alternative. Requires more planning than dusk since it is longer from the mid-day.

4. Shoot by moonlight. Probably requires more planning than dawn or dusk since good moonlight is only possible a few days a month. On the other hand, moonlight provides long shooting windows.

5. Use a pinhole lens and live with the effects of diffraction. They are available for purchase at low prices relative to most good photography gear. There are instructions on the internet for making a pinhole lens from a lens cap.

In short, much of the difficulty can be addressed with technically with a budget that some people may find reasonable. Alternatively, the problem can be addressed with planning and commitment to obtaining the shot. Or both.

In any event, you will probably need a tripod.

Answer 3

Another method, buried in the comments, is to shoot a series of photos and to average them afterwards using an image editing program: https://patdavid.net/2013/09/faking-nd-filter-for-long-exposure.html

Answer 4

When you compose your shot to photograph the lake waves, your meter takes a light reading and sets (probably) a short exposure time. Now if you choose to manually set a much longer exposure time in order to blur the waves, by definition you are going to overexpose your image. In other words, you can't get the benefit of the longer exposure time (blurred movement) without also getting the drawback (vastly increased levels of light hitting the camera sensor).

If you want a long exposure, then you must decrease light hitting the sensor in some other way. You have correctly assumed that using a smaller aperture is one way to do this, but I would suggest (and it has been hinted at, both in the question and in the comments) that you will get the most satisfactory results with a neutral density filter. (Note, it doesn't have to be a variable neutral density filter; a normal neutral density filter will work.)

(Another solution is to decrease the ISO setting, which allows you to use a longer shutter speed, but I imagine you have already hit the limit here.)

If you choose the ND filter route, then the question arises of how strong a ND filter to use. Let's assume you are photographing the lake on a sunny day. The scene might meter at EV 15. That would equate to an exposure in the region of 1/125 sec @ f/16 @ ISO 100. I'm not sure what kind of blur effect you want to achieve, but let's assume you want to use a shutter speed of 8 seconds. Therefore, you would need a 10-stop ND filter. Maybe 8 seconds is not what you want. If you want a longer shutter speed, then you need to wait for a less bright day/time. If you want a shorter shutter speed, you can open your aperture and/or increase your ISO setting in order to expose the scene adequately.