Photography

Photographing Waterfalls: 1000-fold Exposure Range

2011/02/27 By Rob Leave a Comment

When photographing a waterfall (or other forms of moving, turbulent water), the choice of shutter speed determines whether you get a stop-action view of every droplet in motion, or whether you get a smooth, time-averaged view of the currents. What is the best shutter speed to use with waterfalls? I had the opportunity last year to do an experiment, an attempt to answer that question. Of course, there is no single “best” shutter speed. It is a mater of taste and creative vision. But the experiment was useful nonetheless, since it resulted in a visual catalog of how a waterfall looks over a thousand-fold range of shutter speeds.

These pictures were all taken at Niagara Falls, with a Pentax K-7 DSLR, with a Tamron 28-75mm zoom lens at 28mm. There are 21 shots, taken at 1/2 stop shutter speed increments, from 1/6000th of a second to 1/6th of a second. In order to ensure the same exposures while varying the shutter speed I made compensatory adjustments to the aperture and the ISO settings. (With a neutral density filter one could extend this to shutter speeds 2-stops slower.) Post-processing was limited to white balance and cropping.

So what did this tell me? With shutter speed down to around 1/60th of a second, the waterfall looks pretty much the same. From there down to 1/20th of a second you get gradual softening, and at the slowest shutter speeds you get effects ranging from painterly to otherworldly. My favorite is 1/10th of a second.

I suspect the important factors here are:

The speed of the water
The distance of the camera from the water
The focal length of the lens

These combine to determine, from the perspective of the camera sensor, the speed at which the water’s image moves, in pixels/second. If the image is moving at 1 pixel/second, then shutter speeds faster than 1 second will show no blur. But a shutter speed of 15 seconds will show a blur over 15 pixels. I bet if I took the original 1/6000 second shot, loaded it in Photoshop and applied a motion blur until it looked as close as possible to the water in the 1/6 second exposure, I could work backwards to determine the speed of the water.

Shutter Speed	Photograph
1/6000 second
1/4000 second
1/3000 second
1/2000 second
1/1500 second
1/1000 second
1/750 second
1/500 second
1/350 second
1/250 second
1/180 second
1/125 second
1/90 second
1/60 second
1/45 second
1/30 second
1/20 second
1/15 second
1/10 second
1/8 second
1/6 second

How to photograph an asteroid

2010/02/22 By Rob Leave a Comment

Over the years, I’ve seen Mercury, Venus, Mars, Jupiter and Saturn with my naked eyes. And I’ve seen Uranus and Neptune through a telescope. But I’ve never seen an asteroid until last night, when I photographed the 2nd largest minor planet, Vesta.

Vesta is currently near opposition, meaning as seen from the Earth, Vesta and the Sun are 180 degrees apart. This makes Vesta well-placed for observation all-night long, and also means that it is around as bright as it ever gets. So if you are eager to see an asteroid, give it a try some clear night in February or March.

The first step is to find the constellation Leo. Where exactly Leo is from your location will depend on your latitude. But generally, if you are in mid-northern latitudes, a good start is to look to the south-east around 10pm. If you are running Linux, give KStars a try to simulate what the sky will look like. Once you’ve found where Leo is, take a look at this chart showing the location of Vesta [PDF] over the next few months.

Since Vesta is now around magnitude 6.8, it is too faint to see with the naked eye. But it should be visible with even the smallest telescope or binoculars. Compare what you see with the chart. Don’t expect to see any disk or features. It will look just like a star. If you want to be sure, make a sketch of the location of the stars you see in the area, and compare it a night or two later. If it is Vesta, you should see it noticeably move from night to night.

Instead of using binoculars or a telescope, I decided to photograph Vesta. With some trial and error I found a technique that worked rather well.

Obviously, you need a camera that can record the faint stars without so much noise that it overwhelms them. I don’t think a little compact digital camera will work well here. It is all about light gathering ability of the lens. The little lenses in a compact camera will not work well here. But a DSLR can work well, especially if you have a fast lens. Use the fastest (lowest f-ratio) that you have. If the lens is too “soft” at its wide open setting, you can also try stopping it down a stop.
The focal length of the lens is not that important. A big telephoto lens is not going to help here. You are not going to be able to make Vesta look any bigger than just a pin point of light. At the other extreme, if you use a wide-angle lens, your image scale might not allow you to resolve individual stars well. You want something in the “normal” range, not telephoto, not wide angle.
You will need to take a longer exposure, several seconds long, so a tripod is a must, to hold the camera steady. You also want to use a cable release or remote trigger to avoid camera shake. If you know how to set the mirror-up lock on your camera, that can help as well.
You want to take as long of an exposure as you can while avoiding the star images streaking (from the earth’s rotation). This will depend on the local length of your lens and the resolution of your camera. Try exposures in the range of 2-30 seconds.
You will want to set the ISO speed as high as you can without the noise level getting too high. What is too high? Use your judgment. At some point the noise overwhelms the star images.
If you are in a suburban location, you may find that the light pollution causes the image to “fog up”. If so, reduce the ISO speed or decrease the exposure.

In my case, I used a Pentax K20D at ISO 800 with a 50mm f/1.4 lens and a 4-second exposure. The results are as above, which I’ve annotated, as well as a the blown up details When I compared to the chart the extra “star” was obvious. It doesn’t look like much, but that is Vesta, nearly 600km in diameter, orbiting somewhere between the orbits of Mars and Jupiter.

Good luck!

Shooting Daffodils

2009/04/21 By Rob 2 Comments

I like daffodils. I’ve been planting a couple hundred additional bulbs each fall, so that now I have a lovely spring-time display, right around this time.

In past years I would walk through the garden and take a photo here and there, mainly while standing, shooting straight down, not paying particular attention to the lighting or the composition. Flower “mug shots” I’d call them. Then last year, I started doing macro (close-up) photography. Although the results were technically adequate — sharp, detailed closeups — they were…well… rather dull, symmetrical and artless.

This year I’ve decided to try something different. I realized that a flower can be posed like a person. I guess that is obvious in retrospect, but it never occurred to me before that the poses of classical portraiture, like the 2/3 view, over-the-shoulder, profile view, etc., apply to flowers as well as people. And you don’t need to show all of the flower. A close up of part of it can also be interesting.

I’ve also worked to improve my technique, shooting with a tripod and remote trigger, using the McClamp to steady and isolate the blossoms in the field, using small erapertures to get greater depth of field, locking the mirror up before shooting to reduce any residual camera shake, shooting on days and at times where harsh shadows can be avoided, etc.

Here are three examples, intimate portraits, all shot on location in my garden. You can view more on my Flickr page.

China Impressions

2008/11/24 By Rob 5 Comments

While in Beijing for the OpenOffice.org Conference (concerning which I owe you all a report), I was able to spend a little time playing the tourist. I thought I’d share some of the picture I “took”. Each of these images is an HDR image, based on 3-5 source images of the same scene, with different exposures, combined using Photomatrix software.

Although HDR techniques can be used to create realistic-looking (or nearly so) images, in these cases I intentionally step beyond literal reality and attempt an impressionist portrayal of the scene. Jet lag, no doubt, played a small part in my impressions…

First up we have a view of the terrain at Badaling, the popular section of the Great Wall near Beijing. It was a lot colder here than it was in the city, and I was woefully under-dressed. The skies were dull and gray. Standard advice in this situation is to show as little sky as possible. Otherwise you’ll get a dull, ugly, featureless swath of grey. Instead, focus on the landscape and avoid the sky. For low dynamic range photographs, this may be the case, since you cannot bring out any detail in the clouds, but with HDR you can have detail in the clouds as well as the mountains.

I might work on this shot a little more. I think re-cropping it into more equal thirds of sky, background mountains and foreground hills might work well.

Another view at Badaling. It started snowing shortly after this shot was taken.

This is the Boat of Purity and Ease, better known as the Marble Boat, famously restored by the Empress Cixi with funds that were intended for the imperial navy.

The challenge here was that the boat had vivid detail on the exterior, as well as interior details. Expose for the exterior and the interior would be underexposed, but if you expose for the interior, the exterior would be blown out. But if you combine three exposures with HDR, you can get detail all around.

This is the Seventeen-Arch Bridge at the Summer Palace. Don Harbison and I were eying this bridge for much of our visit that day, trying to figure out the ideal vantage point and time for “the shot”. It came around 5:30 that afternoon, as the sun was setting, viewing the bridge from a little strip that juts into Kunming Lake.

At the top of Longevity Hill is the Tower of Buddhist Incense (Foxiangge). This is not a posed picture. In fact, I don’t know who the subject in this photo is, but she looked so relaxed and content that I could not help but quietly steal a few pictures. Some shots take an hour to plan and compose. Others are chance and take advantage of a 10 second window of opportunity. This was of the latter variety.

This picture needs some work in Photoshop to remove the distracting cable going down the column.

This is the Bronze Ox, cast in 1755, looking back to the Tower of Buddhist Incense. I like the ripple of sunlight on the neck. But there is some serious fringing artifacts going on here, under the ears and horns. This shot can certainly be improved on. I keep it as a reminder that I need to return to Beijing and take more and better photographs.

Don’t shoot until you see their eyes

2008/10/21 By Rob 3 Comments

September 18th, 2008
Great Spangled Fritillary (Speyeria cybele)
Pentax K10D with 100mm macro, 1/350 at f/5.6

When I was a child, I did as children do, and chased butterflies in the fields. Forty years later the fascination, if not the boundless energy, still remains.

Is there any logic to the flight of a butterfly? It certainly is not a straight line. Are they following a physically determined path of least action, surfing unseen micro eddies or vortices in the air to conserve their energy? Or are they showing their overflowing exuberance, feasting in a field of flowers, unable to make (and adhere to) a single choice? I know, as child, I was disposed to the latter, perhaps explaining my fondness for butterfly chasing.

In any case I’m older and wiser today. I don’t chase butterflies. I photograph them. Indeed, chasing and photographing are at cross purposes and nearly incompatible. Photographing butterflies is a patient, quiet task. The technique is straightforward and consists of three easy steps:

Go sit among the flowers.
Don’t move.
Wait.

Let the butterflies come to you. As Ptolemy crumbled before the Copernican revolution, this critical change in perspective makes all the difference. Give it a try!