The limiting magnitude of a telescope or binoculars is determined by its
light-gathering power, namely its diameter. Large binoculars may be able
to collect enough light to see to twelfth magnitude, but typical
binoculars are not capable of that. Further, the magnitudes of nebulae are
calculated as if all the light of the object were concentrated at one
point. If your telescope or binoculars magnify the image enough, that
light gets spread out over larger areas, making the nebula harder to
see. Although I am not positive, I would be willing to bet that more
than 90% of the binoculars in use would not be able to see a 12th
magnitude nebula.

The limiting visual magnitude of any optics system, whether it be the
naked eye, binoculars or a telescope is determined by one concept:
signal-to-noise. Can the detector (a camera, CCD chip, or an eye) pick
out the photons of light from an object from the photons of the
background sky. For a totally dark sight, your eye is limited by the
fact that it takes a certain number of photons hitting you per second to
set off the rods in your eye. If you add sky brightness from light
pollution (or from the moon, or from the sun), it gets harder to pick out
those few photons of signal from a star or galaxy from the zillions of
photons inthe background, so the limiting magnitude goes up. So, yes,
telescopes also suffer from a bright sky, which is why observatories in
CA and Arizona are trying to convince their neighbors to keep the lights
down!

Hopes this answers your questions, and thank you for writing.

Sincerely,

Kurtis Williams

"Grief can take care of itself, but to get the full value of
a joy you must have someone to divide it with."
-- Mark Twain

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