Electronic – Sourcing low torque/small stepper motors

One important factor when working with stepper motors is hold torque. You can do some simple calculations based on your camera weight and platform radius to determine the torque due to gravity, and your hold torque should be a fair about larger than that or the motor will slip. You'll also need stepper motor drivers in order to control the motors and provide enough current as well as the proper signal to control the motor. I've had experience with the Pololu A4988 I'm conjunction with Arduino; it's simple to use and only used 2 digital IO pins (at minimum). You can also spare more pins and control things like the driver enable, etc. As for actually choosing a motor, that can be tough. I'd pick a price range and form factor that you'd like to be within and use that to narrow it down. I'd also stay away from the spark fun motors as they are usually on the more expensive end and not the best bang for the buck.

You did not mention what min and max speed is required. I suppose you don't want to make any compromise in any parameter ;-)

With stepper and microstepper driver you can achieve better than 0.15 degrees resolution. But what is precision ? Probably wrong because there is motor and microstepping non-linearity and torque is low, dynamic range is low and extra problems come at very low speed.

You can arrange it as dual loop control with load encoder at outer loop. It should improve precision. Let say 13bit load encoder and 32 or 64 microstepping with 400 step motor might satisfy 0.15 precision.

Gearbox helps with torque and resolution but you also need dual loop control and no backlash if you want change direction. There is extra problem if there is a spring in gearbox. If yes then there is a force at output you need high frequency control loop. It might be even impossible to control system when you must consider this force. So expensive gearbox or back to direct drive.

You can substitute stepper with brushless 3 phase motor and encoder with or without gearbox and one or two encoders. Dynamic range and price go up. Torque ??? For high speed you need high bandwidth encoder/decoder. And it's very difficult to debug such a setup in real time as you almost cannot use breakpoints.

Generally when using encoders they must satisfy your precision needs (and not resolution only).

EDIT (as commenting is forbidden): AS5045/8 encoder: I think you need consider mainly non-linearity INL parameters in range of degrees which affects accuracy (worser than 0.15 deg). Also propagation delay in range of 100 us limits speed, 1RPS = 1/4096 = 244us per position tick.