New to DSLRs? A Beginner's Guide to Exposure and an Explanation of Lens Diffraction
Exposure is one of the most important aspects of shooting with DSLRs. If you’re new to shooting with digital cameras, it can be a bit overwhelming to fully understand all of the terminology and the options for controlling the exposure of the image. Film is pretty straightforward, where the film speed (or ISO, ASA, etc.) does not change. Shooting pictures is a bit more complicated, as the film speed can change, so you’ve got aperture, shutter speed, and ISO as three different settings to affect exposure. Shooting video is a bit different, as the shutter speed of DSLRs will typically not go below 1/30 of a second. We’ve got two videos explaining exposure and control, with the first being a beginner’s guide to overall exposure, and the second explaining what happens as you stop down your lens.
The Three Basics of Exposure and Photography from Matthew Gore:
Taking into considerations all of the factors that affect exposure is important. We must constantly be thinking about what we’d like our image to look like and how the camera settings will get us there. The guide is geared towards still photography, but the same factors apply to video, except of course, for shutter speed, which should stay between 1/30 and 1/60 of a second for proper looking motion. If you’re shooting 24fps, 1/50 is the “correct” shutter speed and if you’re shooting 30fps, 1/60 should be your setting. These will render normal looking motion for the given frame rates. Setting the shutter below these will give you more motion blur and ghosting, and setting above will give a more staccato and stroby feel.
There are certain times when you’ll be outside and your ISO is already at the lowest setting (usually 100 or 200), and the shutter is set at 1/50 or 1/60 for normal motion, but the image is overexposed. You’ve got two options, raise the f-stop, or raise the shutter. In some cases you’ll have to do both if you don’t have any neutral density filters to cut down light, but raising the f-stop too high (usually f/8 and above), may yield less than ideal sharpness in your videos. The embedded video below explains the repercussions for setting the f-stop too high, which exacerbates an effect know as lens diffraction:
The link to the D800 samples can be found here. If you want to get the most out of your lenses, you’ll need to know their diffraction point with your specific camera to get the sharpest images possible. Many professional cinematographers like staying between f/2.8 and f/5.6, as these are usually the sweet spot for lens performance and controlling depth of field (too shallow and they make it difficult for the assistant camera person to keep focus). Though there are certainly times when professionals will be shooting lenses wide open (f/1.3 – f/1.8), they are using much more expensive lenses that perform better than many DSLR lenses. So if you want the best performance from your DSLR lenses, stopping down 2-3 f-stops will usually get you to the “sweet spot” of the lens, and give you the most sharpness, while avoiding lens diffraction.
Once you’re ready to start editing your material, here’s a good resource to get you started.
[via Film School Channel on Vimeo]