Using SpyderLensCal for Video Focus Control

Datacolor’s SpyderCheckr is used to check the auto-focus on still cameras, and to micro-adjust the auto-focus on cameras with micro-adjustment controls in their in-camera menu. However, there are other uses for LensCal. This article describes how to use it to assist with focus setting in video, TV, and cinema capture workflows.

SpyderLensCal showing Depth and Center of Focus

Videography is based on manual focus methods, but SpyderLensCal can still be useful for video capture. Lets start by considering how focusing is done with a video camera. Video focus is manual, and occurs by rotating the focus ring on the camera lens, or manipulating a “follow” device connected to the focus ring.

Geared Ring added to a DSLR Lens, Follow Gear on Far Side

The results of these adjustments are viewed on the LCD on the back of the camera, or on a portable video reference display screen attached to the camera framework. These screen range from small to tiny, so it can be difficult to determine focus on such screens. It is possible to zoom the view on the camera-back display, and sometimes on the reference display, to enlarge a small part of the screen to more effectively check focus. A larger video reference display is sometimes used as well, either in real time, or with a delay, but these screens are not available to the cameraman adjusting the focus controls.

Reference Display mounted on a Camera

Here’s how one or more SpyderLensCal units can improve the accuracy of focus with a video camera. Lets envision a shot where the camera remains stationary, no pan, no zoom, but the focus moves from a glass with lipstick on it in the foreground of the shot, to the face of a woman wearing the same color lipstick in the middle ground. This configuration simplifies the description, as other adjustments to the lens or camera are not needed in this scenario.

To determine the ideal focus for the beginning of the shot, a LensCal is placed on the table next to the glass, and its target plane is aligned with the surface on the glass with the lipstick stain. The camera is is then focussed on the LensCal target, and can be checked, either at full size on a large remote reference display, or by zooming in on the small target bullseye and sloped scale on the camera LCD. The sweet spot in the intentionally shallow focal range will register on the LensCal scale, and the sharpness of the focus will be clear on the target. Adjustments can be made as needed. This position can then be marked on the follow-focus device, or noted on the focus ring. Cinema lenses, with their longer throw, will increase the level of precision possible.

Next a LensCal unit on a light stand beside the actress in the middle ground will be focused on, repeating the process of checking the focus, and marking the correct location. An advanced follow-focus tool with hard stops available at each end would make this process even simpler. Now both LensCal units are removed from the set, and the shot is made, using the start and finish references to assure accurate focus at each end. This technique can also be used for single focus shots, but is particularly useful when there are multiple functions occurring in the shot; being able to remove two variables allows the cameraman to “focus” on the other functions.

So, don’t leave your SpyderLensCal in the dark when shooting video, get it out and put it to use checking the focus on your shallow-focus shots, and improve the sharpness of your video.

Credits: C. David Tobie, Copyright 2013. Website: Return to Blog’s Main Page

Published by cdtobie

This blog covers a range of issues of interest to photographers and those involved in the digital photographic workflow, digital tools and platforms, and fine art output.

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