Why is the double slit experiment different for photons and electrons?

This is a great question about experimental physics. Theoretically, of course, you should get the same results: individual quanta localize at seemingly random spots that, over time, build up an interference pattern:
(From Tonomura's experiments circa the 60s, via Wikimedia)
Practically, photon and electron sources are rather different beasts. Observing interference requires a coherent source; observing individual dots building up into a full picture requires very low power.
A laser is a great source of coherent light. But by design, since it relies on pumped population inversion to stimulate emission to get that coherence, I'd imagine that it's not easy to make a laser low power - certainly not low enough to see individual photons. So you'll be missing pictures (a)-(d), and upon sending your laser through your double slits you immediately see a full interference pattern. (A low intensity interference pattern would also not be visible by eye; it would have to be recorded photographically e.g. by long exposure of a sensitized film.)
Electrons, by contrast, have to be heated off a cathode source, accelerated through a potential difference, and then made a single speed by selecting via magnetic field. If too many electrons make it through your apparatus at high speed, that's a high voltage high current circuit, and I hope your power electronics skills are as good as your quantum physics!
Indeed the whole point of electron double slit experiments was to demonstrate interference even when there was only one electron in the apparatus at a time. Otherwise one could argue that some complicated collective effect, but still classical, was letting the electrons repel each other into some really complicated pattern. But with only one electron in the apparatus at a time, the electron can only “interfere with itself”, which must be a quantum effect.

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