Hello x + C (
),
157.9m I'd say
.
At the very least -
to put an upper limit on it, definetly ~5km (& less), as that is the distance to the observable horizon, at which, by eye, we also see the moon in crisp view, (depending on your height).
As to the lower (near) limit, try it and see before Saturday's eclipse, if that's what you had in mind to set up for. Aperture / f/number) controls the depth of field, so if you have insufficient depth of field with your setup, for the image you'd like to capture, you can use a mask over your scope to reduce aperture and increase your depth of field. A simple circle cut out of dark paper smaller than your existing aperture. Every 1.4x less in diameter is 2x less light, or one f-stop.
Have fun,
Best
JA