I wonder if it's possible to be able to see light frequencies that cannot be normally seen by human eye, without using sensors designed specifically for detecting a certain spectrum range, but rather using some combination of lenses or something else that could transform the light without causing a noticeable latency.
Answer
It's possible to see the wavelengths beyond the red using non-linear optics: Second harmonic generation. Basically two photons combine to form a twice more energetic photon. Green laser works this way.
The opposite of this is the Spontaneous parametric down-conversion, to see beyond the blue. This involves non-linear optics again. In this process one photon splits into two (entangled) photons. Efficiency of this process is very low. (But probably usable to see the UV from the Sun.)
A more effective way is using interference of light of different frequencies. The interference can form a third wave whose frequency can be in the visible light range: $\omega_1 - \omega_2 = \omega_3$. This is the principle of the the optical down conversion. This way you can shift the visible range towards the higher frequencies.
Anyway electronic sensors remain the easiest ways to see the invisible.
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