he theory behind modulation transfer function and exactly how it pertains to electro-optical systems is already well described in all the relevant textbooks. Being that it’s broadly speaking the measure of the ability of an optic system to transfer different degrees of detail from real-life object to on-screen image, it is essential that this quality is thoroughly examined before any electro-optical system is permitted to be utilized in the field. Be sure to learn up to you can about this type of testing and you’ll understand its importance in military avionics.
The Crucial Nature of the Function
You’ll often find modulation transfer function testing simply referred to as an MTF test. It really is widely considered to be a very useful optical function to test as modulation copy is what is partially in charge of the generation of sharp, detailed images often seen and acted upon in military avionics.
It can be used to ascertain the quality of many aspects of a given electro-optical system, including all sorts of different lenses from the most convenient you can imagine all the way up to multi-element lens assemblies. Ultimately, ensuring equipment passes an MTF Test is what allows us to benefit from an individual specification that includes high resolution at the same time as high contrast.
Typically, each of the following components has associated transfer functions that require to be checked using simulation and MTF Testing boards.
Lens
Camera sensor
Image capture boards
Video cables
How MTF Relates to Other Functions
Transfer functions in general exist whenever a response is related to a stimulus, or in other words when an output is produced consequently of a particular input. As such, these functions are usually found in fields such as seismology and, of course, military avionics.
An overall function known as optical transfer function is what gives us a description of how optical systems like infrared cameras react to a variety of pre-defined stimuli. This function is itself made up of two parts, where MTF corresponds to its magnitude and PTF describes the phase components.
Methods and Instruments to work with
There are several ways in which you can test the function of your infrared optical system to check on the contrast and resolution produced. Ultimately there are four main methods you should be aware of.
Discrete or continuous frequency generation
Image scanning
Video-based methods
Interferometric approaches
The accurate measurement of this vital parameter included in a thorough quality control test means that your equipment can fulfil its intended functions completely.
Building an Efficient Approach
When it comes to testing approaches, one of the main considerations is standardization. You want each stage of the procedure to be repeatable in a trusted fashion that corresponds to real applications. Simulation protocols can be developed by making use of specially designed testing boards that make use of the principles of black body radiation to improve the reliability of your tests.
When testing equipment that captures infrared and near-visible radiation, it’s incredibly difficult to use sources in these wavelengths as a calibration standard that can be reliably used. The key reason why is because they cannot be spatially extended and radiating uniformly in all of the direction within a given hemisphere. However, integrating spheres are made perfectly for this reason.
Typically, integrating spheres are constructed in such a manner about allow the use of various filters to limit certain wavelengths at particular times. The end result is that you can examine the qualities of modulation transfer function under a variety of conditions subsequently applicable to real-life scenarios.
