Common Configurations
| Negative
Lens |
This test setup is best suited for
Negative lenses.
The setup for testing a negative lens
is essentially the same as the one designed to test an object
at infinity. The only difference is that the image
formed by the lens is virtual, and is located on the
near side of the lens.
However, there is an important additional
limitation on testing negative lenses, so the setup
is presented as a separate section.
|
Typical Setup
The collimator is on the left, and the
microscope is on the right. This setup requires that the working
distance of the microscope lens be longer than the BFL
of the lens under test. |
Schematic
Representation
 OpticStudio
hardware works in conjunction with PixelScope software.
While no programming is needed, it is necessary to enter
the parameters of the setup and the nominal parameters
of the lens under test. The picture above shows how
these parameters are entered.
|
Limitations
The limitations noted in object
at infinity apply to testing negative lenses. In
addition, negative lenses have an additional limitation:
- The working distance of the microscope
lens must be greater than the BFL (back focal length)
of the negative lens. The working distance of the
4X lens is 22 mm. Wells Research offers other closeup
lenses with working distances up to 200 mm.
Just
as with positive lenses, it is desirable that the NA
of the microscope objective be larger than the NA of
the lens under test. Otherwise only the central part
of the lens contributes to the measurement.
However, if you just want to
measure the EFL of the lens then the NA requirement
becomes less important. |
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