[Sven]"Is it not possible to playback 2048 x 1556 @ 24fps?"
Yes it can, however most modern post workflow is based on 23.98 so that you have a realtime conversions to video and correct sync for audio.
"Are there no possibilities for aspect ratios other than 2048 x 1556 and 2048x1080 ?"
those are the acquisition frame sizes, there are a couple of great tips for various output formats by using the DS keyer function in the Kona Control panel and by using a Mask file created in photoshop you can output various frames to tape.
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