Choice of motor for a camera stage - stepper or servo?

Hi
So I've got myself a shiny new Uno to build a robotic photography stage that I want to build in several stages.

First part is to get controllable rotation of the specimen stage - something that'll take a max of a kilo and rotate it very slowly indeed - in the range of 1 rotation per day or per week ( even slower would be good ), changing direction is also essential. I'd need a bare minimum of 1500 steps per rotation.

Whatever I choose is going to need some serious stepping down from the motor speed but I've no idea whether to go down the stepper route or servo route - servos seem easier to set up but I'd presumably need to add an encoder wheel to measure rotation.

Any thoughts on which motor technology I should be concentrating on ?

Next phases will be replacing the camera intervalometer with the arduino ( should be easy ) then adding a mount so I can move an SLR in arc over the stage, if that goes ok a tracking rail but one thing at a time.....

I'd go with a geared down stepper, like 8:1 gearing. I think 1.8 degree stepper are pretty common, so 200 steps per revolution, 8:1 gear down will yield 1600 steps per revolution.
Steppers can be moved with some control pulses and then will sit there.
Servo's need constant PWM type signal to hold a position.

Mechanical stuff not really my area, but this approach makes sense to me.

The only argument against steppers is the constant power they take when stationary,
so if you were contemplating battery-power that would be an important consideration.

You need to work out the maximum rotation rate you need(*), the minimum angular step
of the turntable, and the torque needed, then you can work out the motor and gearing.

(*) this would be important, say, should you want to reset to initial position in a hurry -
if you had massive reduction gearing this wouldn't be very feasible.

You need to consider backlash - you want to change direction and maintain accurate
position so the gearing would probably need to be anti-backlash. How many steps per
revolution would you really like?

With a kg load you need decent bearings in the gear system (assuming the load isn't
always perfectly centred on the turntable).

Steppers need constant power? I thought you gave them some pulses, and they kind of dropped into the next step position. Servos I could see needing constant power.

Thanks for the advice
ultimately 3000+ steps would be great - it would let me do a 2min time lapse with a 360 rotation, backlash wouldn't necessarily cause me trouble - a couple of paused frames in a direction change wouldn't be noticeable, worse would be a skipped position that could spoil the whole sequence.

I'm going to have to sync the rotation to the shutter at some point - for the moment that'll just be down to setting the interval on camera and table very carefully but that has limitations.

It's got to be mains power so that's not an issue - the camera can't run for weeks without it. For resetting the stage I thought about having a sprung loaded cog - we use them on fraction collectors at work - just hold it out of the way to move the stage quickly.

I'll need a device to stop me peeking - it's all too tempting on a three week run to have a look but it invariably jogs the camera, or causes air movement to disturb a subject, some sort of electrified spike pit should do there ....

Pinhole camera aligned with main camera POV to provide monitor function?

Got a spare low end smart phone that should do the job and send me updates wirelessly, ultimately I might try hooking that up to the arduino so I can control the stage by remote.

Does running a stepper very very slowly for weeks on end have any implications for the motor's lifetime?

You're not really running it tho - you give it a pulse/pulses infrequently to make it move a step or two. The rest of the time, no power is applied.