How do you estimate the aperture needed to produce sufficient depth of field for a given subject?
Suppose I am facing a bicycle from the front and use whatever combination of focal length and subject distance is necessary to have the bicycle completely fill the frame. I focus on the handle bars as I would like this to be the sharpest point of focus. How can I best estimate the aperture needed to ensure that entire length of the bicycle is within acceptable focus?
I have tried using my camera's DOF preview button, but the resulting image is too dark in the viewfinder to determine the depth of field.
I could use a DOF calculator, but this would take too long.
I could take a few shots at varying apertures, but again, this would take too long.
What methods do you use to visualise depth of field in situations like this?