42 second shutter speed (different subject)

Disappearing Act and Long Exposures

A while back, I posted a couple of long exposures on Facebook (see the post here) and asked if people could tell which one had been exposed for 1/30 of a second vs 29 seconds. It was a little confusing because the shot with the higher exposure value (that is, it was brighter) was the one with the 1/30 of a second exposure.

I thought I would explain the purpose of the exercise and talk a bit about how I achieved super long exposure times (shutter speeds) in bright sunlight.

First, if you know nothing about how a given exposure value was achieved other than the shutter speed, you cannot draw a conclusion about whether a brighter image has a longer shutter speed than the darker image. As a reminder, there are 3 settings that determine exposure: aperture, ISO, and shutter speed. The same exposure can be achieved with vastly different shutter speeds by adjusting the ISO and aperture to offset the difference.

So, if all you know is the shutter speed, what differences can you see that will tell you which had the longer exposure time? From an artistic perspective, we choose shutter speed based on whether we want to show or freeze motion. “Showing motion” means motion blur becomes visible in an image. So, our first test is “how much motion blur do we see?”

However, with this particular subject, the clouds are not moving quickly. The clouds are our best clue as to how long the shutter was open. But the clouds moved slowly enough that the difference in motion blur between the 1/30 of a second exposure and the 29 second exposure is relatively subtle. When you compare the 1/60 of a second exposure to the 77 second exposure the difference becomes far more obvious.

Likewise, moving water is usually a great clue as to how long an exposure is. As the exposure gets longer, fewer ripples in the river show.

The third difference you might notice if you look very closely is that the highway that curves around the river has no cars on it in any of the images with a 29 second or longer exposure time (shutter speed).

This happens to be one of the cool reasons to do super-long exposures. It’s a way of removing traffic and crowds from a scene. “But WAIT!” you ask, “What happened to slow shutters showing motion blur?”

Disappearing objects are the extreme of motion blur. The moving objects don’t reflect enough light relative to the total light signal to register as part of an image. This is a big difference in how cameras “see” vs how we see. We do not have a time factor that increases or decreases the exposure of what we look at. A camera, however, continues to gather light, exposing the image for the length of time the shutter is open in a quantity determined by the aperture size. How much light is needed to get a given exposure is then determined by the ISO.

So, why does this make moving objects disappear? Well, let’s look at the trees in our long exposure examples. They’re very dark. They reflect back less light than the river next to them. But they are sitting still, standing in one place, reflecting back that little bit of light in the same location for the duration of the open shutter. It’s enough to register a dark image of a tree. By comparison, the cars on the freeway are driving through the frame. They reflect only a little more light than the trees, but only for a split second in each point along their trajectory–the accumulative effect of the open shutter is lost on them. They would have to be very bright to register in the image–which is how you create light trails when cars have their lights on.

So, the bottom line is that if you can get your shutter slow enough that moving objects can’t reflect enough light to show up in the image, you can make them disappear.

The next question is, of course, how do you get a super slow shutter in daylight? We can stop down the aperture as much as possible (to the point before diffraction causes our images to fall apart, but that’s another subject) and we can turn our ISO as low as it will go, but at 7:52PM in July (more than an hour before sunset), that only got me a 1/30 of a second shutter speed.

All of the example images have the same aperture and ISO settings. Having reached the limits of my camera’s ability to control exposure, my only other option to get a slower shutter was to block some of the light reaching my camera’s sensor. To do this, I used a Heliopan 10-stop neutral density filter.

So what is a Neutral Density (ND) filter? From a technical perspective, an ND filter is called “neutral” because it is designed to block all colors of light equally. In other words, the color of the light should not be affected by an ND filter, just less light should make it through the lens.

That said, 10-stop ND filters reduce the light that reaches your sensor by 1000x. Many result in a color shift. In the case of the Heliopan, it’s a red shift. The good news is that it is something easily corrected via white balance settings in the case of the Heliopan (not true of all ND filters). I personally like the color shift in these examples and didn’t bother to correct it–it was like sunset came early.

To get the identical exposure with a 10-stop ND filter, if you are changing only the shutter speed, you would need to multiple the shutter speed by 1000. So, 1/30 becomes  33.33 seconds. If you really want this shutter speed, you need to use the bulb setting on your camera with a remote and time how long the shutter has been open. I did successively longer exposures using the Bulb setting to see what I liked best.

Neutral Density filters give you more control over light. They let you use much slower shutter speeds or allow you to open up your aperture significantly in brightly lit conditions where this isn’t otherwise possible.

If you like playing with motion or shallow depth of field in bright light, neutral density filters are a great option to explore.

The water cannons at night at Coolidge Landing in downtown Chattanooga, TN

Lesson 108 (All Cameras): Long Exposures

Note for iPhoneographers: the SlowShutter app will allow you apply this information to the iPhone, although stabilizing the iPhone (even in an iPhone tripod) can be challenging.  See Lesson 101.

When I teach beginning photography workshops, one of the things I spend a lot of time working with students on is the relationship between exposure and artistic expression.  Shutter speed is one of the big ways in which we control both exposure and motion showing in our images.

Slow shutter speeds leave the shutter open for longer periods of time, allowing more light to reach our sensors for exposure.  They also allow any motion in the subject to blur.  Most of us strive for tack sharp images, so why would we ever use long shutter speeds?

First, sometimes you have to use a slow (long) shutter speed if you’re shooting in low-light conditions.  Second, allowing motion to blur can create some cool artistic effects.  And third, if you need lots of depth of field, you’re going to need a small aperture.  The age-old analogy for the relationship between the shutter speed and the aperture size is to think of a water faucet.  How long you turn the water on is like your shutter speed.  How wide you open the valve is like your aperture.  If you turn a water faucet on wide open for a split second, you can get the same amount of water as if you turn the water on at a trickle but let it run for a much longer time.  That’s how aperture and shutter speed work together to control the total volume of light that will reach your sensor and why using a small aperture usually means a slower shutter.

Let’s start with an example that was both low-light and a small aperture, but with no motion:

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This example was shot at twilight with a 1 second exposure at f/18.  F/18 is a small aperture opening and 1 second is a slow shutter speed.  By using a tripod and a 2-second delay on the shooting mode, I was able to keep the camera still and avoid introducing motion blur.  I got the exposure I wanted and kept everything from the rail in the foreground to the building in the background sharp.

Now let’s take a look at what happens if you don’t keep your camera still:

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In this example, I literally picked up my camera/tripod and moved it in about the last second of a 25 second exposure.  Because the building in the background is so much dimmer than the lights going up the path, the building did not blur while the lights, being so bright, created trails across the image.

Now let’s talk about using long shutter speeds to show motion in the subject itself.  Waterfalls are a popular subject for this technique.  By putting the camera on a tripod again, everything in the image that is still remains sharp but the moving water blurs to a soft “flow” through the image, visually communicating the movement of the water.

Compare this image (shot at ⅙ of a second) to the one after it (shot at 1/320 of a second):

The fast (1/320) shutter speed freezes the splashes of water while the slower shutter speed (⅙) allows the water to blur into softness.  Which one you prefer is a matter of taste (in this case, I like the faster shutter speed better, but that’s partly because it’s slightly less exposed and has less flare from the sun).

Now let’s look at an example of low-light, moving water, and lots of depth of field:

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This was a 20 second exposure shot at f/16.  The small aperture not only provides more depth of field, but it also turns the lights on the bridge into stars.  The slow shutter allows the water coming out of the water cannons to blur into soft streams.  Also notice the surface of the river–the splashes and ripples have also smoothed out into soft lines.

There are many more fun things you can do with a long exposure, but I’ll save those for future posts.  🙂

This is not an iPhone shot, but it's a better example of light trails.

iPhoneography Lesson 101: Slow Shutter App and a Highway Bridge

I introduced the Slow Shutter app several posts ago, but this time, I dug out my iPhone tripod and found a view of a highway bridge over a river so I could demonstrate this app creating light trails.

3GSphoto of 5S

First and foremost, this requires a tripod.  Here is a shot taken with an iPhone 3GS of my iPhone 5S in its nice little tripod courtesy of Photojojo (they have crazy accessories for iPhoneography that will make you feel like you’re buying Barbie photography gear).  The one I have came with a telephoto attachment and works fine on flat surfaces, but if I had no interest in the telephoto attachment, I would go for the $15 Gorillapod.  Just something to keep in mind for the post-Christmas shopping frenzy.  🙂

If you decide to buy something, Photojojo is offering $5 off to both you (if it’s your first-time order) and me if you use this link to go to the website:  http://photojojo.com/r/afvu–a win-win deal!

To create the Slow Shutter images, I used an 8 sec exposure under the light trails settings.  Below, find the two steps required to set this up plus what to do after you shoot:

Once you get your camera set up and going, you can keep adding to the exposure.  In this example, I did a series of 4, 8-second exposures over top of each other before saving the final image.  The key is not to move the iPhone at all when you do this.  Any vibration from tapping the phone or in the tripod it’s sitting on shows up in the image.  The problem I experienced was that I couldn’t tap the screen firmly enough without moving it to get the camera to focus on the subject, leaving me with soft focus on the distant bridge.  Here are two images on the tripod, both with soft focus:

All-in-all, I’d have to say that Slow shutter is a great idea, but probably not a useful app if you just want to pull the camera out of your pocket and start shooting.  In case you’re curious what it would do if you just hand held the iPhone, here’s the best I could do hand-holding:

Your Assignment:  Do you have an interest in being able to capture light trails at night?  Is it worth it to you to have a tripod for your iPhone to capture such images?  If so, Slow Shutter is a great app to experiment with.  We’ll also take a look at using Slow Shutter with panning in future lessons.  In the meantime, give it a try with cars driving by and see if you can get the results you’re seeking.

 

 

 

30 second exposure where foreground boats were very brightly lit

Lesson 91: Use a Tripod

Long ago, in Lessons 25 and 34, we talked about holding your iPhone to maximize stability and even using a tripod, particularly for using a telephoto attachment lens with your iPhone.  Well, if ever there was a time to use a tripod with your iPhone, it’s with the Slow Shutter app.

Because I was on a shoot with my DSLR on a tripod, I was able to capture some cool light trails to share with you in the gallery.  However, I was without the tripod for my iPhone, so the best I could do was to prop the phone up on a rock wall and try to hold it still, resulting in this:

15 second exposure while trying to balance the iPhone on a rock
15 second exposure while trying to balance the iPhone on a rock

Let’s talk about what happens when you use a slow shutter.  “Slow” means the shutter will stay open for a long time (relatively speaking) before it closes again.  When we use a “fast” shutter, the shutter only stays open a fraction of a second.  The shorter the duration the shutter remains open, the less the subject can move in that fraction of time, so the less blur you will get.

When the shutter stays open for a very long time, like in these images (shot with 15 and 30 second shutter speeds), as the subject moves, the shutter is still open, so it records the moving image.  If you’re moving around, you get a complete mess.  Or, you can get some fun art if you’re particularly talented at moving your phone around.

I mentioned in lesson 90 that you can use Slow Shutter to get light trails, such as cars driving by at night.  Since I don’t have examples of that yet, thought I would go ahead and share the light trails from a lighted boat parade even though they were taken with my DSLR.  Don’t worry–I will eventually get light trails with the Slow Shutter app!

Your Assignment:  Find a location where you have a clear view of a street where cars drive by on a regular basis.  Go after dark–this is a great time of year for this assignment in the Northern hemisphere with the early sunset.

Either use an actual iPhone tripod or come up with a way to prop your iPhone so it will not move.  You need to be able to completely let go of the phone or your movement will jiggle it.  Set your exposure time for about 15 seconds–this depends on how much traffic is going by.  You can do 30 seconds if you have a long line of cars that keep passing or fewer seconds if all lights pass through the frame in less than 15 seconds.

Are you able to get a nice, sharp light trail from the headlights and tail lights of the cars?