|
Methods: The FPM system uses a Raspberry Pi computer and 196-LED matrix light source. FPM images were reconstructed using in-house Python code. The MTF was determined from bar-patterns using a least-squares analysis to fit a square wave, including odd-harmonic terms, to image profiles through the bars. These were normalized to larger uniform regions of the pattern and combined to generate the MTF. Results: Total component cost of the FPM was less than $200. The theoretical diffraction limit imposed by the pupil function of this system was 280 cycles/mm, slightly less than the measured MTF 10% frequency of 300 cycles/mm. The 10% frequency in FPM images was 550 cycles/mm. Conclusions: The USAF test pattern provides a practical method for assessing FPM performance in terms of the achieved MTF of the $200 Raspberry Pi based Fourier ptychography microscope. The limiting frequency in FPM images, 550 cycles/mm, was slightly less than the Nyquist sampling cut-off frequency of 670 cycles/mm imposed by pixel spacing. |
|
|
