Hi Clemens,
yes, it have to be high speed IR-Diodes (TSHF5410/TSFF5410 or TSHF5210/TSFF5210 or similar) with rise times in the 25..100ns range or little more. Normal speed IR-LEDs with typical 0.5µs or so rise time is not enough, but works at lower distance range. (About 1/4 to 1/3 or less that far)
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