I just purchased a Nikon D5500 to replace my old D100 (yes, it has been that long). I was wondering if and how I can use my SB-50DX flash with it. I'm not clear on which mode it has to be in or what settings to use. Thanks!
The information you seek can be found on pges 327-328 of the D5500 Reference Manual:
Other Flash Units
The following flash units can be used in non-TTL auto and manual modes. Use with the camera in exposure mode S or M and a shutter speed of 1/200 s or slower selected.
Notes on Optional Flash Units
Refer to the Speedlight manual for detailed instructions. If the flash unit supports CLS, refer to the section on CLS-compatible digital SLR cameras. The D5500 is not included in the “digital SLR” category in the SB-80DX, SB-28DX, and SB-50DX manuals.
If an optional flash unit is attached in shooting modes other than [no flash], [night vision], and [selective color], the flash will fire with every shot, even in modes in which the built-in flash can not be used.