For lenses that focus out at long distances, to verify sharp focusing on distant objects you will need a resolution test target system that produces an image that is near the hyperfocal distance your lens is focused at.
The size of your imaging plane at a distance, based on your lens’ angular field of view can be calculated using our Chartfinder Utility.
As your desired test distance becomes longer, filling your camera’s entire field of view with a single conventional resolution test target such as the eSFR ISO or SFRplus becomes geometrically more expensive and difficult as a larger test lab is required.
Physical Target Systems
It is possible to assemble extremely large test chart systems, but the process of producing, mounting and protecting a large test chart, and achieving uniform glare-free lighting becomes more costly and complicated as you increase your necessary test distance. Contact our charts department at firstname.lastname@example.org if you are interested in these sort of test targets.
For testing long focal length zoom lens’ ability to focus on a distant object, including space and remote sensing applications, it may become cost prohibitive to use a physical target system. Outdoor tests are complicated by atmospheric distortion and durability of the target.
Target Projection Systems
An optical system that projects a virtual image that appears at or beyond the hyperfocal distance can serve to simulate a real target system.
Projection systems are key for long-range testing within a factory environment, where long distance target cannot practically be included inside of each production line. A conversion lens (also known as relay lens or collimator) can convey the image of a smaller, high-precision test target which appears at a longer virtual distance.
Precisely aligning the test chart with the collimator lens and the unit under test so that all parts are aligned on a single optical axis becomes the challenge with this solution. Any lens system will focus best in the center, and the on and off-axis quality of the conversion lens affects the measurements that you obtain. This means that measurements you take, and how they are compared to any of the pass/fail requirements will need to be adjusted to consider the loss of resolution due to the collimator.
Multi-target Projection Systems
As it becomes less viable to obtain a high-quality target that covers all the location on your lens that you are interested in testing, a single test chart that fills the field of view may be replaced with a smaller target projection system that is directed into the lens.
This also makes the job of precisely aligning the test target projection with the entrance pupil of the unit under test that much more difficult, and precise engineering expertise becomes necessary.
Our partners at Optikos designed the Meridian™ Production Camera Testing System to projects multiple SFRreg compliant targets into your camera system. This enables rapid testing of the full field of a high-resolution camera focused at an infinite distance within a very compact test fixture.