Friday, December 15, 2017

Back To Basics: Shutter Speed

Continuing on from previous entries What the ISO? and Aperture Labs we're going to look today at shutter speed, specifically as it applies to night shooting.
So what is a shutter? Well, Gavin over at the amazing YouTube channel The Slow Mo Guys did a  video showing it better than I could. Seriously, it's amazing. I'll wait for you to watch.


Welcome back. So now that you know what a shutter is, and what it looks like, let's do another one of those fancy animations showing a sequence of pictures taken with different shutter speeds. In this case it's a static object. We'll look at the effect of the shutter on moving objects some other time.

As you can see from the series of images above as we expose the sensor for more and more time, we get a brighter image. The more astute reader may also notice that the amount of noise in the image is relatively consistent regardless of the exposure. So what lessons can we take away from these two observations?

First, to shoot an image at night, or when we're in a dimly lit environment, we can increase the amount of time the sensor is exposed to get an image that is bright enough to see.

Second, the added light comes with no (significant) additional noise. For complex reasons this isn't entirely true*, but its close enough for our puropses.

So what's the drawback? Well as Gavin explained, a long exposure will cause additional motion blur. For extremely fast moving objects, you may capture an image that shows two completely different events at the same time. But there's one more problem. The motion doesn't necessarily have to be caused by something in front of the lens. In fact the camera shaking can ruin the picture.

As a general rule, anything slower than 1/60th of a second needs a tripod. This is something that I'd recommend testing out for yourself. If you have particularly steady hands, you may be able to manage exposures as slow as 1/10th or 1/20th. If you have shaky hands, you may need to limit hand shooting to 1/100th of a second.

In later installments, we'll look into the effects of shutter speed with moving subjects. If there's something you'd like to see, or something here that's left you scratching your head, let me know and I'll try to clarify it. In the mean time, have fun and keep shooting.

* We'll talk about diffraction spikes and signal-to-noise ratios in different blog posts.

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