One of the camera questions I get most often is, “What size lens do I need for this distance?”
The first thing I need to know is the camera's sensor size. Then I need to know what you want the shot to look like.
A camera positioned one hundred feet from the stage could be covering the whole stage, a panel discussion, or a tight shot of one presenter. Those are three different framing requirements from the same position.
My starting point is the camera, the distance, and the shot. Once we have those, we can make a useful lens calculation instead of guessing.
Start with the shot the camera needs to deliver
Before I compare lenses, I want to know the tightest and widest shots that camera needs to cover.
Is it providing a close presenter shot for image magnification, or IMAG? Does it need to pull back for a panel? Will it also be responsible for a full-stage view?
A reference picture or a quick framing sketch helps. “We need to see the presenter from the waist up, with room for movement” tells me more than “we need a long lens.”
When you describe the frame, include the headroom and movement space. A six-foot-tall frame means the entire image covers six feet vertically at the subject position. It does not mean the presenter has to be six feet tall.
That distinction matters when you put the numbers into a calculator.
Confirm the camera model and active sensor area
Sensor size is the first piece of information I ask for because it changes the relationship between focal length and framing.
For a 2/3-inch broadcast camera, I would start with the appropriate sensor format in the calculator. But I would not assume every professional camera has that sensor size. Give me the exact camera model and the mode you plan to use, especially if that mode crops the image.
The Points in Focus calculator includes a 16:9 2/3-inch/B4 format using 9.6 × 5.4 mm dimensions. I use the 5.4 mm sensor height for the planning examples in this article.
If your camera's active image area is different, the answer changes. Confirm that information before treating any example here as a lens recommendation for your package.
Measure the distance to the presenter position
I need the distance from the actual camera position to the actual subject position. The overall room length does not give us that by itself.
Mark the lectern, the front and back limits of the presenter's movement, and any other presentation area the camera needs to cover. If the camera is off to one side, use its viewing distance to the subject.
I would also ask whether that camera position is confirmed. Seating, sightlines, access requirements, and room-layout changes can all affect where the camera ends up.
If the position moves, run the numbers again. The lens that fits the original drawing may not cover the same shots from the revised location.
A simple camera lens distance formula
A useful first estimate at typical stage distances is:
Focal length in mm ≈ sensor dimension in mm × subject distance ÷ desired frame dimension
Use sensor height with frame height, or sensor width with frame width. The subject distance and frame dimension need to use the same units.
Example: A presenter shot from 100 feet
Using a 5.4 mm active sensor height, a camera one hundred feet away, and a six-foot-tall frame:
5.4 × 100 ÷ 6 = approximately 90 mm.
Now keep the camera in the same place, but tighten the frame to three feet vertically:
5.4 × 100 ÷ 3 = approximately 180 mm.
Same distance. Different shot. Twice the focal length in this example.
That is why I cannot choose the lens from the distance alone. These are calculated starting points, and I would still confirm them against the actual camera, lens, and framing during setup.
Lens focal length examples for live event cameras
Here is a quick reference using that same assumed 5.4 mm active sensor height. The frame measurements describe the height of the entire image at the subject position.
| Camera-to-subject distance | 6-foot-tall frame | 3-foot-tall frame | 2-foot-tall frame |
|---|---|---|---|
| 50 feet | 45 mm | 90 mm | 135 mm |
| 75 feet | 68 mm | 135 mm | 203 mm |
| 100 feet | 90 mm | 180 mm | 270 mm |
| 150 feet | 135 mm | 270 mm | 405 mm |
These values are estimates, rounded to the nearest millimeter. They do not transfer unchanged to a different active sensor size.
I would use a table like this to narrow the lens range, then check that the compatible lens covers all the required shots. Getting the tight shot is only half the job if the director also needs a wide view from the same camera.
How to use a camera lens distance calculator
I have used the Points in Focus Depth of Field, Angle of View, and Equivalent Lens Calculator for years. It is a useful place to start when someone asks me which lens they need.
For framing, this is the sequence I recommend:
- Select the correct sensor format, or enter the active sensor dimensions.
- Enter a candidate focal length in millimeters.
- Enter the subject distance, checking whether you have selected feet or meters.
- Compare the calculated field of view with the shot you need.
- Adjust the focal length and check the other required subject positions.
The calculator also includes aperture and depth-of-field information. Its documentation recommends Method 1 for video/cine lenses and internal-focusing designs.
The numbers help us plan the package. I still want a framing check with the actual camera and lens from the final camera position.
What else should you check before renting a lens?
Once the framing calculation looks right, I want to check the whole camera package.
- Mount and image coverage: Is the lens compatible with the camera and its active image area?
- Usable zoom range: Can the lens cover both ends of the assignment, from the widest shot to the tightest?
- Exposure: Can the package deliver the intended exposure under the planned stage lighting at the focal lengths you will use?
- Support: Are the tripod, head, platform, and any required lens support appropriate for the package?
- Controls: Does the operator have the focus and zoom controls needed for the position?
- Sightlines: Can the camera see the subject when the audience stands or the presenter moves?
During setup, put someone at the relevant stage marks and check the shots. Give the operator a chance to follow that person through the expected movement.
The calculation should get you close. The rehearsal tells you whether the complete setup works for the assignment.
