What's the smallest instrument you've ever used to view the night sky? My smallest is a 6×15 monocular about the size of a cigarette pack. How are the views? Well, frankly, though I'm no big-aperture snob, 15 mm is not very satisfactory for astronomy.
So why do I use it? Well, it's so small that I can carry it essentially everywhere I go — even walking to the corner store. That's mostly handy when an unusual bird turns up. But every now and then I also get an unexpected urge to view something in the night sky.
The tiny monocular's not much, but it's better than my unaided eyes. It does a fine job on the Moon, and it'll usually show two or three of Jupiter's moons as long as I rest it against a solid support. And the views of M44, M45, and the Hyades aren't half bad.
My 8x32 monocular is in an entirely different class. The 6x15 gets used by accident; this one I bring intentionally. When I'm observing in the city, everything has to go down and up 2½ very tall flights of stairs. And when I'm carrying two telescopes, or my Dob plus an SLR on a tripod, there's a real premium on weight and bulk. That's when I bring the monocular instead of my 10x30 binoculars.
I rarely purpose-view deep-space objects (DSOs) with the 8x32 monocular, but it's very handy for picking Mercury out of the twilight, locating mag-6 stars in the city, and working out star-hops in advance.
Last Friday the Moon rose a half hour after the end of astronomical twilight — not long enough to settle in for serious telescopic observing. So I decided to spend the time seeking out DSOs with the 8x32 monocular. I ended up viewing 20 Messier objects plus my favorite small-instrument open-cluster triplet: IC 4665, NGC 6633, and IC 4756.
Rather than use charts to locate my targets, I used my 15×70 binoculars as a "finder" for the little monocular. Bright DSOs popped out immediately through the bigger instrument, enabling me to work out a star-hop to be used with the monocular. The method was fast and effective, but after the rich, luscious view through big binos, the little 8x32 inevitably seemed feeble by comparison.
The discrepancy was most striking on M8, the Lagoon Nebula. Sure, the monocular showed the nebulosity easily, but the view was lackluster, a far cry from the 15×70 binoculars' jaw-dropping image. With a couple of exceptions, the globular star clusters were also a disappointment, showing either as bright but nearly stellar or faint and nearly stellar.
Things were better with the open star clusters and wide-field vistas. Many of the brighter clusters resolved into individual stars, and IC 4756, though unresolved, was a lovely ethereal glow. The star cloud M24 was impressive, and M18, M17, and M16 lined up neatly above, all fitting easily into a single field of view.
For something that slips easily into any coat pocket, the 8x32 monocular does a surprisingly good job. So what's the smallest instrument you've enjoyed using to view the night sky?