Ridiculously Small Optics

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.

tiny optical instruments
Here are my three smallest optical instruments, with some familiar obects for scale. Right to left are: 6×15 monocular, 8×32 monocular, and 8×25 binoculars. Each fits easily in a coat pocket, and the entire collection weighs 20 ounces. The 8x25 binoculars give marginally better daytime views, but I prefer the 8x32 monocular for astronomy.
Tony Flanders
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?

11 thoughts on “Ridiculously Small Optics

  1. Enrico the Great

    OK, Mr. Flanders used a smaller aperture than I did, but, I used a lower magnification. I observed the sky from a VERY light polluted Queens New York with a 4×21 Bushnell fixed focus binocular marketed mainly to sports fans. I bought it at the same time as I bought a very nice pair of 6×30 Leupolds, the salesman actually tried to dissuade me from buying the Bushnells without even trying to sell another brand.

    The wide field of the inexpensive binocular actrually showed a nice swath of sky, a good part of the Big Dipper fit into the field of view. I can’t wait to try it under realy dark skies! A fair number of stars were vissible even through the light pollution. This is were IDA fears to tread! My observing session was quite short, can’t wait to try again!!!!

  2. Stephen

    The smallest instrument i’ve used is a pinhole in a cardboard box, for solar viewing. That’s much smaller than naked eye, even with one eye closed.

    I want to make one with a long tube to get a larger image. Should take 10 minutes to find the bits and assemble. Cheap too. What am i waiting for?

    Then i’ll want to do astrophography with it.

    But i use 8×21 binoculars all the time. 3.5 oz (100 grams). Fits in my pocket. My 8×42 binoculars are 21 oz (595 grams), and seldom get used. If i really want to see something, I have a 240×254 monocular. Fit’s in the car.

  3. jim clark

    I had a 2 inch f-6 achromatic lens that I finally made into a telescope. All it took was plastic plumbing tubing. The mount is just up- down movement done with right angle brackets screwed together, and just turn the whole base left or right. It works best at 30 power. I use it to identify planets and ckeck where the terminator is on the moon, before getting out a larger telescope. It is also great for sunspots with eyepeice projection. I used it for the transit of Mercury- which it did show as a spot about as big as a period.

  4. Steve Bell

    I’ve used a pair of 10 X 25 roof prism binocs (really cheap) that I keep with
    me, but the optics are so poor, they’re pretty unsatisfying (read stars are
    really ‘star-shaped’). The wife’s 10 X 30 Canon IS are another story
    entirely. For quick ‘grab and look’, they’re amazing. Wish a pair of 15 X 50’s
    was in the budget.

  5. Steve

    Although not especially small I’ve especially enjoyed my 8.5×44 wide angle binoculars. I took them and my 8″ SCT to a dark sky site one evening that turned out to be exceptionally transparent. I enjoyed “discovering” dozens of DSO’s and then discovering their names/designations in Bright Star Atlas 2000.0. When the night was over the 8″ SCT was still in it’s case!

  6. John

    I was in Japan when comet Machholz made an appearance. I couldn’t make it out with the naked eye from the city so I bought a pair of 100 yen binoculars (that’s around 1USD). I guess they were something like 5 x 20. The optics were awful with really bad chromatic abberation away from the centre of the field of view. Also the lenses weren’t very well aligned so it took your eyes a few seconds to merge the two images. Nevertheless, from where I was the comet was completely invisible to the naked eye, and clearly seen as a resolved blob through the plastic lensed binoculars which cost less than a can of coke.

  7. Robert Gillette

    Smallest instrument I’ve used to view the night sky was a binocular device with lens apertures of about a quarter inch and a focal length of maybe an inch — my eyes.

  8. paul rapp

    Several years ago I bought my wife an 8×21 Nikon binocular for use while we rode our bicycles. It met our requirements perfectly: small, lightweight, easy to store and retrieve and it has great optics. We don’t ride much now, but the qualities that made that little Nikon great for cycling make it perfect for a quick look at the sky; day or night. Thank you, Nikon, for my one and only glimpse of Comet Macholz.

  9. NS

    My usual equipment is an 8X42 binocular. I have what I think is the same 8X32 monocular you do but don’t care much for it as an astronomical instrument. For the moon and planets I have a 4.5 inch telescope but for open clusters the binoculars give a nicer view.

  10. kevan hubbard

    I travel a lot so cant carry around large binoculars so regularly use a 8×25 Opticron monocular,infact I shall be taking it to Australia in Feb.,Id say that you can see down to about the 8th mag.with it.The focus is very good with no flare around stars or planets.Things like M27 are quite easy with it but M51 always escapes me although Ive picked it out with an 8×42 monocular.

All comments must follow the Sky & Telescope Terms of Use and will be moderated prior to posting. Please be civil in your comments. Sky & Telescope reserves the right to use the comments we receive, in whole or in part, and to use the commenter’s username, in any medium. See also the Terms of Use and Privacy Policy.


This site uses Akismet to reduce spam. Learn how your comment data is processed.