SLR video cameras and the newer large sensor video camcorders, are often used with photography lenses -- which provide outstanding optics at amazing cost savings compared to lenses specifically designed for film/video. A superb photography lens may cost $2,000; about 1/10 of what a good cinema lens or servo zoom ENG style lens costs.
However, if you think you're going to get $20,000 worth of function for $2,000 I have some bridges and swampland I'd like to sell you. Every time a new camcorder is released we have 30 people who want to rent the lens Famous Video Guy used when he made the demo videos for the manufacturer because his footage was incredible. They forget that Famous Video Guy also had 8 techs, 6 manufacturer's reps, and a sound crew on the set and spent two weeks shooting multiple takes, making sure all the weaknesses were minimized and the strengths emphasized.
When someone tries to reproduce that look on a real world budget with a limited crew they're disappointed that the lenses they chose didn't work like they assumed they would. Photo lenses aren't video lenses, don't behave like video lenses, do things differently than video lenses. Like any good tool, they can be extremely effective when used properly. But if you don't take the differences into account when planning equipment for a shoot they'll be just as effective as using a sledgehammer for computer repair. So in an effort to prevent assumptions (because we all know what assume means) we put together a little reality checklist.
You'll notice that the word photo(graphy) is underlined every time it precedes the word lens. We added extra emphasis here. Photo lenses are not video lenses. They can be used for video if you work around their limitations.
- There are no wide aperture 10x photo zooms. If you need one lens and wide aperture, you need a $20-40k video zoom.
- Less expensive photo zooms are variable aperture. That is they may be f/3.5 at the wide end, but maximum aperture may be f6.3 at the long end.
- Photo zooms are NOT parfocal. If you zoom, you will have to refocus when you get where you are going. If you plan to zoom AND maintain focus, you will need an amazingly gifted assistant. (There are a very few exceptions listed in "This article".)
- Many photo zooms telescope when zooming. As in the lens can get 3 times as long zoomed in as it was when zoomed out. Support equipment must take this into account.
- Most photo lenses have electronic aperture control. You will need to select a lens or adapter that allows manual control if you want it.
- If your camera supports electronic aperture control, realize this is noisy. You do not want to use a camera's internal microphone if you are using electronic apertures.
- If your camera has electronic aperture control, realize this does what it wants, not always what you want. If you change from f2.0 to f/2.8 it may do go to f/16 or f/1.4 on the way there. Yelling at the camera doesn't help. Yelling at us doesn't help. Yelling at the lens doesn't help. It's like the changing of the tides: you have no influence on it.
- On those lenses that have mechanical aperture rings, they will click at given stops. They are not smooth and continuous like video lenses.
- Photo lenses breathe. If you change focus you will usually change image size slightly.
- Focusing throw on photo lenses is very abrupt. A video lens may turn 360 degrees during focusing. Photo lenses generally turn 120 degrees at most.
- Critical focusing is less accurate on photo lenses. And don't ever try to use the distance scale. They are wildly inaccurate.
- Autofocus is not critically accurate. When shooting SLR video autofocus microadjustment must be set up before the shoot if you want critically sharp focus. But if you really want accurate focus you'd best pull it manually. Not an issue at f/5.6 usually, but usually an issue at f/2.0
- When autofocus is available with an adapter (certain Panasonic and Sony cameras) it will be very slow and often inaccurate. There is often a tendency for the lens to "hunt" for focus.
- Electronic photo lenses are noisy. Electronic aperture control, focus motors, and image stabilization systems all make interesting buzzy sounds. If you use an in-camera mic they will ruin your audio (on-camera shotguns are often, but not always, OK).
- f/stop is not T/stop. An f/2.0 lens is probably close to a T3.0 lens, maybe a bit faster. Depending on the manufacturer the f/stop rating is either a rough estimate or a boldfaced lie.
Some General Recommendations
If you've read this and are thinking "well now I don't know what to do" good! We may have prevented you from wasting an entire shoot. We'll give a few quick, general suggestions:
- Don't plan on using in-camera audio if you're using any of the lens electronics (stabilization, autofocus, electronic aperture). A camera mounted shotgun mic may be enough isolation, but not always.
- If you can use prime lenses, that's best. If you must have a zoom realize you'll need to repull focus after zooming. Staying in focus during a slow zoom with a photo lens requires amazing skill and practice.
- Use only f/2.8 fixed aperture zooms. Variable aperture zooms are extremely difficult and usually of lesser image quality.
- Manual aperture control is usually best (Older Zeiss and Nikon lenses have manual apertures). Adapters with manual aperture control are available even for some electronic aperture lenses (Zeiss, Nikon, and Sony).
- Unless you've shot the specific lens and camera combination before, allow yourself at least a full day of practice. I guarantee you Famous Video Guy (or his staff) did.
If you have questions about lens selection, please send us an email at firstname.lastname@example.org We'd much rather figure out what's best on the front end than hear about how the lens didn't do what you assumed it would after your shoot.