framerate issue with ffmpeg zoompan filter

with a lot of searching on this board, I've been able to put the following ffmpeg command together. It creates a clip of an image scaling from 1.00 -> 1.12x over 240 frames @ 24p (10 seconds).

ffmpeg -loop 1 -i myphoto.jpg -vf "zoompan=z='min(zoom+0.0005,1.12)':x='iw/2-(iw/zoom/2)':y='ih/2-(ih/zoom/2)':d=240" -c:v libx264 -pix_fmt yuv420p -t 10 -s hd1080 -r 24 -crf 10 myvideo.mp4

However, when this command is ran, I get a 10 second clip, with the zoompan 'resetting' to 1.00x at around 9.5 seconds. Upon checking the rendered video in Quicktime's video inspector, I'm finding the FPS to equal 23.7, not the 24 I've set with -r 24. Am I looking over something here?

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