Tuesday, November 16, 2010

Step by Step : Shooting Video with the DSLR

Controlling Exposure

One of a series of posts aimed to help still photographers produce better videos with their DSLRs.

So, now that we have the camera all set up and the neutral picture style dialed in, let's go out and shoot.

Remember, with video, it's best to have everything on manual so select your frame rate (24, 30 or 60p) and your white balance setting. Choose your iso, aperture and a shutter speed, keeping in mind that for the smoothest, natural look, you should keep the shutter speed at twice your frame rate in what is referred to as the 180 degree shutter rule. You also need to keep the aperture constant in a video sequence. For example, you are panning a scene…you don't want the aperture to change during your pan. The viewer will notice the depth of field changing as you pan - not good. Also if there are extreme shutter speed changes, even these will be noticed, especially with movement. So, auto exposure is not recommended.

With video, you need to change the exposure manually and the best way to do this is with a variable neutral density filter. What a variable ND filter does is allow you to rotate it's filter ring (similar to a polarizer) and dial down or up the amount of light hitting the sensor. It becomes like your aperture in that it controls the light, but unlike the aperture, your depth of field remains constant. With this, you can control your exposure, keeping the same aperture and shutter speed, despite the changes in the ambient light and you can do it smoothly while shooting if need be.

A variable neutral density filter can be somewhat expensive, costing anywhere from around $125. to nearly $400. depending on the manufacturer, but to me, they are worth every penny. They usually give you up to 8 stops reduction in light which will allow you to shoot wide open apertures in full sun for that coveted shallow depth of field that seems to be all the rage these days. When purchasing a filter, buy the filter that will fit your largest diameter lens and use a step up ring for the smaller lenses.

Of course you could skip the expense of a variable ND and go with a few less expensive standard ND filters. They work perfectly fine, in fact, they are usually optically better than a variable ND. Only drawback with these is that as the light changes, you need to stop shooting and switch filters or change your aperture.

For more info about the 180 Degree Shutter Rule, check out Tyler Ginter's excellent post. He can explain it much better than I can.

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