I have built a driver that enables me to use my Sony A57 (no remote/usb) in combination with a FTDI bulb cable and a FlashAir WiFi card. This driver is very easily modified for your camera. Actually, since the D5100 and A57 have the same sensor, I think you just need to delete the FlashAir components.

This driver lets me auto focus and frame on a DSLR with no usb tether capabilities. It is still a work in progress, but you are welcome to try it

github.com/StarryJapanNight/indilib_sonya57

If you wait a week, I will make it more generic, with FlashAir being optional.

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