A 3.3 μm polycyclic aromatic hydrocarbon (PAH) filter was used to study the photochemical evolution of PAHs in the reflection nebula NGC 7023. The filter is narrow, Δλ=0.09 μm, and isolates the PAH emission. The plate scale is 0.475 arcsec/pixel and the angular resolution is about 2 arcsec, dominated by telescope jitter. FORCAST also performed observations of NGC 7023 (at 11.2 μm) and the combined data shows a peak in the 11.2/3.3 μm ratio, corresponding to PAHs of ~50 C-atoms. This supports models claiming the photochemical evolution of PAHs is size-dependent and most efficient for PAHs with ~50 C-atoms.