Working with Long Exposures

I’ve recently added two post with long exposure seascapes, one from Torrey Pines State Beach (the photo below is from that set), the other from the Point Loma tidal pools (just yesterday). What astonished me was the high “yield” of keepers or rather, images I consider worth showing for the moment, in relation to the total amount of photos made during the outing.

At Point Loma, we spent about three hours photographing, and I came home with 8 unique frames (I capture more individual frames because I test exposure and composition before I make a long exposure), 6 of which are contained in the post (the other two were detail/abstract photos that didn’t really work out). I’m quite happy with the results. I guess long exposures and the time it takes to make them helps focus and awareness, and reduces the amount of photos that contain a lot of “maybe” from the beginning. I hope to be able to carry that mindset over to other photos as well, not just long exposures. :)

More information about how I photograph long exposures is provided below the image, for those of my readers who are interested in the more technical background.

Black & white photo from Torrey Pines State Beach, San Diego, CA by Alexander S. Kunz
Flat Rock & Cliff, Torrey Pines State Beach, San Diego, CA.

When I first became interested in long exposure photography I waited until after sunset to get conditions that would allow for exposure times of 30 seconds or more. Needless to say, that was not exactly the most fulfilling approach – dawn and dusk are relatively short here in Southern California (20-30 minutes), which doesn’t exactly leave a lot of time to try and experiment. I was lucky to get 2-3 images at one time.

My approach has changed, of course. Today, I do not wait until after sunset. Instead, I’m using a 6-stop and/or a 10-stop neutral density filter, often in combination with a polarizer (which adds another 2-3 stops).

I found that best conditions for long exposures are actually overcast days (not just because cloud movement looks really cool too when it’s blurred by a long exposure), and luckily, we get a good dose of them here in the form of the (otherwise dreaded) marine layer – a coastal fog that moves in over night, burns off during the day, and reappears in the evening (ruining people’s sunset photos, haha).

On overcast mornings and afternoons, there’s enough light to make it easy to set up the camera. In the 30-60 or so minutes before sunset, and after sunrise, the light is still not as strong and you can get some really long exposure times with ND filters.

There are a couple of challenges with long exposures, and I want to describe the methods that I have developed to comfortably work around them in my workflow. And needless to say: there are a number of different approaches to tackle these challenges, depending on the equipment used, personal preferences, and whatnot. My methods may not be the most efficient, or easiest, or most straightforward for anyone else but me. I just like to share them – for the sake of sharing. :)

The two most obvious obstacles are composition and metering. Obviously, I compose (and focus) without the filter on – with a 10-stop ND, you hardly see anything in the viewfinder. Live view might work even with the filter on, depending on the type of camera you use (for example, I’ve heard that Canon has better gain than Nikon). With the 10-stop filter, it’s definitely a no-go, but I can use it on the D800 with the 6-stop filter if I open up the lens.

Personally, I have removed the AF activation from the shutter button for the longest time, and only use AF-ON to activate the AF (this is often called “back button auto-focus”). If you’re activating your AF with the shutter button, you may want to switch the camera to manual focus once you have your composition and focus before you’re putting the filters in place (otherwise, the camera will try to re-focus, and may not be able to do so with the filters on).

I’m using screw-in filters (the round type; B&W ND filters from Schneider Kreuznach), and it is a bit bothersome to attach and detach them to and from the lens for every new composition. Using a XUME adapter may make that a bit easier (I haven’t tried these, but a friend who does is quite fond of them). Round filters also eliminate any light leaks between the filter and the lens. When you’re using square filters (Lee, Cokin, Singh-Ray, HiTech, etc.) you have to fiddle with the filters holders and may have to take care of light leaks, but in return it’s much easier to add/remove the filter. And if you want to use a graduated filter, there’s really no way around using square filters.*

When I first began working with long exposures, I also metered without the filter and then either did the math, or used an app on my phone to calculate the correct exposure. I can honestly say that this was the biggest nuisance, as it often left me with exposures that were simply “off” – it’s not exactly motivating to find out that your exposure time was way too short after waiting for 2 minutes (and the extra 2 minutes for the noise-reduction/dark-frame subtraction to finish)…

So I don’t do that anymore. Because no matter how precise your calculations – they often do not match the “filter reality”: a 10-stop filter might not be exactly 10 stops, but maybe 9.5 or 10.5 stops – and at the exposure times I’m aiming at here, 1/2 stop can be quite a difference – if you’re at 2 minutes and need 1/2 stop more, that’s one more minute. Isn’t it nicer to just wait a little longer for an exposure to finish than having to repeat the whole exercise?

So what am I doing instead? I put the filter in place once I have my composition and focus, and set the camera to a really high ISO (depending on the situation, that could be ISO6400, for example – 6 stops faster than ISO100) and do a test exposure – hey, it’s digital, lets utilize its advantages, shall we? Important at that point: cover the viewfinder, or the meter readings will be way off. And I mean WAY off. :)

For the test exposure, I aim at relatively short exposure times (maybe one second or so, depends on the situation) because I only look at my histograms. With a 10-stop filter it may be useful to open up the aperture a bit as well (which means I might be using f/4 for my test exposure, instead of f/11 for the final photo, you get the idea).

Most of the time, I find that I can add an extra stop to the exposure with the filter versus the one without a filter. This may have to do with the strong vignetting that the round filter introduces (see photo above), so your mileage may vary depending on the type of filter you’re using. And you have to be careful with breaking ocean waves: the white wash is rather bright, so you may want to watch your camera’s exposure meter a little bit to see how it changes as the waves roll in, and set it to the shortest time it indicates. Again, better to get it right at the first attempt than having to repeat the whole ordeal because of blown out highlights.

Once I have the best exposure setting, I first set the target aperture (if I had to change it for metering my test exposure), then just lower the ISO and watch the exposure time reading from the camera. Eventually, I reach the 30 second limit of the camera that way and have to switch to “Bulb” mode – but from that point on, the math is usually fairly easy. If I’m at ISO800 and the camera shows me a 20 second exposure time, then the next stop (ISO400) is 40 seconds, ISO200 is 80 seconds, and ISO100 (the base ISO of the D800) is 160 seconds, or 2 minutes and 40 seconds. Easy enough even for a math dork like me. :)

The advantage of this method for me is that I can NEVER forget to lower the ISO after metering. Been there, done that. 12 minute exposure at ISO6400 instead of ISO200. Quite a lovely result, really. ;-)

The darker it gets though the more difficult things become, and the more important test exposures become. For the 80 second exposure below (made in bright desert daylight), I had to stack the 10-stop and 6-stop filters, and the camera’s meter reading was way off (2 stops). With my high ISO test exposure method and checking the histograms, I was able to manually find the correct exposure settings easily, nevertheless.

Space, a desert photograph by Alexander S. Kunz
View of East Butte Borrego Mountain from West Butte Borrego Mountain, near Ocotillo Wells, CA. February 2013.

One of the problems that I haven’t found a working solution for is using the polarizer, or rather, seeing when it is actually reducing glare. I’m using a thin mount polarizer to minimize vignetting on the wide end of both the 16-35/4 and the 24-120/4 so it has to be the last filter when stacking, and in combination with a 10-stop ND, it’s quite hard to see when it’s rotated to the right position. I’m using a bigger eye-piece on the camera (it’s actually made for people wearing glasses) and if I look into the viewfinder for a couple of seconds while covering my other eye with my hand I’m able to sometimes see a little bit of the polarizer’s effect, depending on the situation.

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