Shutter Speed for Photographing Raindrops

HOW TO PHOTOGRAPH RAIN – STOP MOTION – WITHOUT FLASH – and, ‘Neglecting Air Resistance’ hehehehe

I get the question – OFTEN – How to Photograph Rain?

This is really a question that takes two sciences into account – Physics and Photography.

Now I get to say the famous Physics statement:  “Neglecting air resistance, and all those other pesky things that slow down stuff…”

“It depends on the size and weight of the raindrop how fast it falls: the heavier, the faster.

At sea level, a large raindrop about 5 millimeters across (house-fly size) falls at the rate of 9 meters per second (20 miles per hour).

Drizzle drops (less than 0.5 mm across, i.e., salt-grain size) fall at 2 meters per second (4.5 mph).

A raindrop starts falling and then picks up speed because of gravity.

Simultaneously, the drag of the surrounding air slows the drop’s fall. The two forces balance when the air resistance just equals the weight of the raindrop.

Then the drop reaches its terminal velocity and falls at that speed until it hits the ground.

This simple view neglects updrafts, downdrafts, and other complications.

[Source:  http://answers.yahoo.com/question/index?qid=20080721133907AA88bh4 ]

So, let’s say that our raindrops are big raindrops and they fall at 20mph (9 meters per second).

Now, as a photographer, I want to know what Shutter Speed I need to use to stop those raindrops in Stop Motion.  By knowing what shutter speed will create stop motion images, I can also know what shutter speeds I can use to create blurring effects.

We need to know the formula to figure out Motion Blur – that formula is:

MOTION BLUR = OBJECT VELOCITY X SHUTTER SPEED

Let’s say that the raindrop falls at 9 meters per second, or, 9,000 mm per second, and you set the shutter speed of your camera at 1/250th of a second.

MOTION BLUR = 9,000 mm per second x .004 of a second

Then, the MOTION BLUR would be 36 mm.

Let’s increase the Shutter Speed to 1/1,000 of a second.

MOTION BLUR = 9,000 mm per second x .001 of a second

MOTION BLUR = 9 mm.

At 1/1,000 of a second, there is still 9mm of MOTION BLUR.

OK, we are still not there.  Let’s increase the Shutter Speed to 1/1,500th of a second.

MOTION BLUR = 9,000 mm per sec x 1/1500th of a sec, or

MOTION BLUR = 9,000 mm per sec x .0007 of a second.

That would give us a MOTION BLUR of 6 mm!  Still NOT at Stop Motion:  Let’s increase the Shutter Speed to 1/2,000th of a second.

MOTION BLUR = 9,000 mm per sec x 1/2000th of a sec, or

MOTION BLUR = 9,000 mm per sec x .0005 of a second.

Using a Shutter Speed of 1/2000th of a second, the MOTION BLUR is, 4.5 mm of MOTION BLUR.

How Frick’en Fast does the Shutter Speed need to be (without using flash), to create a STOP MOTION IMAGE of RAIN?

Let’s continue, shall we…

How about if we really go wild and try 1/5,000th of a second shutter speed:  That would be .0002 of a second.

MOTION BLUR = 9,000 mm per sec. x .0002 of a second

Considering a big raindrop traveling at 9,000 mm per second, and using a Shutter Speed of 1/5,000th of a second, the MOTION BLUR is still at 1.8 mm.

We are going to go totally wild now, and say we are using a 1/9,000th of a second Shutter Speed.

MOTION BLUR = 9,000 mm per second x .000111 of a second, thus,

MOTION BLUR = .999 of a mm.

Could you live with 1mm of motion blur in your rain photography?  Yes?  No?  Maybe?  If not, then what is it going to take to get that damned rain to stop moving?

1/12,000th of a second Shutter Speed?  Let’s give it a try.

MOTION BLUR = 9,000 mm per second x .0000833 of a second.

MOTION BLUR at .0000833 of a second would equal, 0.7497 of a mm.

This is getting ridiculous!

HOW ABOUT, 1/25,000th of a second Shutter Speed?

MOTION BLUR = 9,000 mm per second x .00004 of a second.

**MOTION BLUR, at 0.00004 of a second Shutter Speed, still equals 0.36 of a mm.**

Shall we do 1/100,000th of a second Shutter Speed? Why not…

MOTION BLUR = 9,000 mm per second x 0.00001 of a second.

The MOTION BLUR of a big raindrop falling at 9,000 mm per second, and using a Shutter Speed of 1/100,000th of a second, is 0.09 of a mm.  That may be about as close as I want to continue going, to find the STOP ACTION Shutter Speed needed to capture a big raindrop that falls at 9,000 mm per second.

You can attempt to use ultra-fast flash with high-speed shutter settings to stop rain in motion, but that is another Physics and Photography story.

Does that answer the question about “How to photograph rain?” – I’m not sure if it does because it depends on what effect you wish to get – stop action or blur motion.  If you use flash, you can illuminate rain drops better to give that sense of stop motion.  However, if you are depending on capturing raindrops using ambient light (diffused cloudy sunlight), then you will need a heck of a fast shutter speed.  If the equation, BLUR MOTION = Distance Traveled per Second x Shutter Speed, is accurate, then, to stop that big raindrop traveling at 9,000 mm per second, will need, approximately, a 1/100,000th of a second Shutter Speed to get near STOP MOTION images.

Perhaps a camera like this would do the trick to take Rain Photographs, http://www.optronis.com/produkte/high-speedkamerascr/cr4000x2.html

We are Forgetting What May be the Most Difficult Thing about Photographing Rain!

Rain is WET – Really Wet!  To photograph rain properly, I hate to tell you, but you will need to get out there in the rain and photograph it.  You can expect to get wet, and your equipment is also likely to get wet.

And, to get macro shots of rain is even messier!  You need to get pretty close to your small subject to get decent captures.  Of course, you can use a longer focal length macro lens and stand back a bit, but not too much.  Rain is small, really small. When rain hits the ground (or any object, it explodes and get everything around it wet, including the front element of your lens.

It is pretty hard to capture good rain drop photographs between wiping the front element of your lens.

If you are a one-man-show, the difficulties multiply:  Now, you need to focus on your subject, keep your camera secure, steady, ready, and dry, all the while, timing your shots to attempt capturing raindrops as they fall from the sky at 9,000 mm per second.

You may be holding an umbrella in one hand, and focusing and clicking the shutter button in the other hand.  Oh, and don’t forget, wiping the front of the lens, and camera body, of rain water.

Photographing rain out in the “wild” is no easy task.

That’s not to say, don’t do it, do it, give it a shot!  Have fun with it, but attempt to keep your equipment as dry as possible because water and electronic gadgets don’t mix very well.

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