What is a Lens Test Chart?
It’s a way for you to test if the distance markers on your lens are reporting the correct focal distances for different focal planes. If a subject is a certain distance from a lens and the focus-puller is using the distance markers on the lens to pull focus, it is important that the lens distance markers correspond correctly with real-life distances. Testing lenses in this way ensures they work well and are reliable during your shoot, as well as over their lifetimes.
Example of a Lens Test Chart courtesy of B&H
How to use a Lens Test Chart:
- Mount the lens you want to test to a camera. The lens should have distance markers, and the camera should have a monitor or viewfinder attached.
- Mount the camera to the tripod. Ensure that the plane of the camera sensor is parallel to the plane of the test chart. This usually means that your sensor has to be at the same height as the center of the test chart.
- Decide what distance marker you would like to test first. Place your camera at that distance from the chart. For example, if your lens has a 5ft distance marker that you would like to use for the test, place your camera 5ft from the test chart.
- Look at the lens test chart through the viewfinder or monitor of the camera, and use the focus ring of the lens to pull focus to the chart. The markings on the chart should help in assessing whether the image is sharp.
- After ensuring the chart is in focus, look at the distance markers on the lens. If the lens is working correctly, the focus should be set at the distance marker you are trying to test. For example, if you are testing the 5ft marker, when the image is in focus at a 5ft distance from the chart, the lens should also say that the focal plane is 5ft away from the sensor. It should be at the 5ft marker.
- Do the same test at a couple of distances to ensure the lens is working correctly.