Sunday, August 15, 2004

Adjust speed for focal length

Let's discuss focal length requirements before we approach Exposure Value (EV) changes as needed to shoot night and indoor sports.

Use proper support to ensure a stable image. However, also set the shutter speed to facilitate a sharp image with the lens used.

The rule for stable image quality is: use a shutter speed faster than the focal length of the lens. On zoom lenses, set the speed for the maximum focal length (200mm for an 80~200mm zoom, 35mm for a 17~35mm zoom). For simplicity, I'll give whole-stop examples. Third stops could be an obvious choice for those using professional cameras with fractional settings. Use the rule above to find the correct third stop for the lens focal length.

35mm = 1/60
100mm = 1/125
200mm = 1/250
300mm = 1/500
600mm = 1/1000

A shutter speed slower than the suggested speed requires major stabilization of the lens (tripod) or excellent breath and body control.

The resulting shutter speed is considered the minimum shooting shutter speed with each lens for assignments. PJs need to make EV adjustments to ensure the minimum speed, minimum film ISO and appropriate aperture setting.

Enough for now,


tristanh said...

So, if I were to take a shot with a 50mm lens, and used say a 1/16 shutter speed, I'd likely get blurring on the subject, or would that depend on lighting and fstop as well?

Mark M. Hancock said...

It depends on your support. On a good tripod, you can shoot stable objects with hour-long exposures. Hand held, you're likely to get blur.
If you have enough light or ISO speed to increase the shutter speed to more than 1/60th, it's the best option.