to the extent that (3) will still be met.

While challenging, producing magnetic lenses is essentially a solved engineering problem. In condenser lenses C1 to C3, intermediate and projector lenses, the maximum field utilised is significantly less than 1 Tesla, far from saturating any components of the magnetic circuit. The condenser-objective requires a higher field, reaching 1.5 T in the present work, however it should be considered that this field is generated by a pair of single turn solenoids without a pole piece. It is therefore anticipated that lenses of a few thousand amp-turns and pole pieces constructed from a modern high performance soft metal alloy will allow such magnetic fields to be achieved without saturation.

Temporal Compression
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To deliver 10 fs pulses over the flight distance necessary to include magnetic lenses, active compression is required. In [@Kealhofer2016] the compression and characterisation of ultrafast electron pulses using an aluminium resonator excited by 0.3 THz pulses was demonstrated. Optical field enhancement around the resonator yields electric fields of 10$^6$ V/m, compressing picosecond electron pulses by a factor of 12 over a distance of tens of centimetres. Timing issues are inherently minimized as the laser which drives the photoemission is also 