Understanding Binocular Exit Pupils

Exit pupils

Do binoculars with small exit pupils really produce dimmer images?

One binocular specification that seems to generate more than its share of contradictory advice is exit-pupil size. I’ve often seen statements to the effect that you should avoid binoculars with smaller exit pupils because the view is “dimmer” than in models having larger exit pupils. But is this actually true, and more importantly, should it factor into your binocular selection?
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Gearing Up for a Moon Shot

Moon shot

Taking your own trip to the Moon doesn’t require anything as big and expensive as a Saturn V rocket, but a little equipment will definitely make the voyage more rewarding.

The Moon is unquestionably one of the most appealing sky sights. We’re drawn to it as though some primitive impulse from deep within rises to the surface whenever we see the lunar disk shining from the darkness, like consciousness itself. And it’s simply beautiful. No wonder it’s the subject of countless poems, the lead player in numerous nursery rhymes, and usually the very first target for a beginner’s telescope.
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Gary’s Easy-Go-Round Binocular Mount

Easy-Go-Round Mount

Build this simple device for steady binocular views of the night sky.

I love binocular astronomy. At least, that’s my excuse for cluttering the house with a dozen (at last count) of these double-barreled optical wonders. Recently, my collection expanded to include particularly heavy 10×50s and inexpensive 15×70s. For the first time I really felt that I needed some kind of binocular support.
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Binoculars By The Numbers

Binocular numbers

Choosing binoculars is easy once you understand the specs.

Shopping for binoculars at your local camera store or on-line can be a bewildering experience. And if stargazing is your goal, the task becomes even more confusing — there are so many factors to consider and so many (often contradictory) opinions about what matters and what doesn’t. Fortunately, once you understand some of the basic specifications, figuring out whether or not a given binocular is going to suit your needs becomes a lot easier.

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Sizing Up the Newtonian Secondary

Secondary mirror

Too big, too small, or just right? Making sure your reflector’s secondary mirror is the correct size is a straightforward task.

The Newtonian reflector has many strengths, not the least of which is that it consists of just two elements: a precisely shaped paraboloidal primary mirror and a flat diagonal secondary mirror. Yet for all its intrinsic simplicity, confusion abounds when it comes to the optimum size of the diagonal. Many amateurs, and apparently even some telescope manufacturers, seem unsure as to how to choose the correct size for the diagonal. So how big should it be? That depends on several design parameters and some personal preferences.
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