Auto-focus is great for photographers, but not for capturing moving subjects. What you need is a trained eye, a steady hand, and a good follow focus.
When you take a look at the best cinema lenses money can buy, auto-focus is nowhere to be found. All the motors, image stabilization and fancy electronics of our DSLR lenses are by and large firmly part of the photographic world. Their cross-over and use in video is simply a result of the fact so many of us shoot video on what is fundamentally, photographic equipment.
Auto-focus is a concept that doesn’t even exist for most seasoned professional cinematographers. The idea that you would not have direct, tactile, hands-on control over the most critical aspect of your image just doesn’t make a lot of sense.
How Does It Work?
A follow focus is simply a mechanical geared device which translates rotational movement of a knob on one or both sides of the camera to a drive gear engaged with a geared focus barrel on the lens.
Cinema lenses have permanently geared focus and iris rings and additionally cinema zoom lenses have a geared zoom ring. A temporary gear ring can be installed on suitable photographic lenses also.
Manual Focus Lenses
Some lenses are more suited to follow focus use than others. A follow focus system works with manual focus lenses that have a direct mechanical drive from the focus barrel on the lens. This includes all cinema lenses, and some, but not all photographic lenses.
When looking at electronic DSLR or mirrorless camera system lenses, there are some lenses with a direct mechanical manual focus mechanism, these can be used with a follow focus system.
However, some DLSR and mirrorless camera system lenses use electronic focus only, and feature a “fly-by-wire” manual mode where movements on the focus barrel of the lens are translated digitally to control the focus motor. This is generally not going to work with a follow focus system.
With cinema lenses the positions of the geared rings do not change, this is something to keep in mind with some photographic lenses… the lens barrel itself may extend and contract changing its position relative to a follow focus drive gear. These lenses also make the use of a matte box difficult, or impossible depending on the amount of movement.
Choosing a Follow Focus
Here’s some quick tips to keep in mind when you are looking for a follow focus.
- Budget – A follow focus can range between a couple hundred dollars and a couple thousand dollars. As is the case with matte boxes… you do get what you pay for. Some camera accessories are fine to choose based on budget alone but a follow focus and a matte box are two items worth spending decent money on (same goes for tripods incidentally).
- Backlash – Some cheaper follow focus units will have noticeable play or backlash in the gearing. This results in a degree of dead movement where rotation of the knob does not translate to the lens immediately, and a change in direction requires this slack to be taken up in the gearing. In a purely professional sense there is zero tolerance for any play in the gearing, but at lower price points it may be unavoidable, so make sure it is minimal.
- Try Before You Buy – It’s one thing to read product reviews online, it’s another thing altogether to get your own hands on something. Here at UBMS for instance, you are encouraged to get hands-on in our showroom.
Materials and Build Quality
Camera accessories take a lot of abuse, and need to serve you for a long time. Cameras change all the time, but a good follow focus, as with a good matte box is universal and should last you well beyond any camera. Make sure the build quality is solid, this doesn’t have to mean heavy, but invest in quality once, and you won’t have to waste money later on replacing it.