More on Scopes and Binoculars

A couple of years ago, I wrote a series of blogs comparing big binoculars and small telescopes. The subject has continued to fascinate me ever since, and I'm now planning to write an article about it in Sky & Telescope — tentatively slated for the May 2010 issue.

Tony Flanders
A couple of weeks ago, when two weekday nights near new Moon were forecast to be clear back-to-back, I took a day off from work to observe some more objects from Deep-Sky Wonders columns and to compare the three instruments shown at right: a pair of Fujinon 16x70 binoculars borrowed from Dennis di Cicco, my 70-mm f/6.9 refractor, and the Orion 4.5-inch Starblast.

I'm still working on the fascinating — though ultimately unanswerable — question of what sized telescope is equivalent to any given pair of telescopes. How good is the brain at combining the light seen through two separate eyes?

Pretty good, it would seem. Across the board, the images through the 16x70 binoculars are clearly superior to my 70-mm telescope at 16X. More surprisingly, I've actually found some cases where the binoculars beat the StarBlast running at 18X, using both higher magnification and much more aperture. In particular, the elusive outer loop of the Orion Nebula — the broad, extremely faint circle of light that stretches from Theta through Iota Orionis — is actually easier to see in the binoculars. Stay tuned for more details.

9 thoughts on “More on Scopes and Binoculars

  1. Tony Flanders

    The binoculars in my photo are mounted on the Orion Paragon-Plus parallelogram mount. A very nice mount, but far from the best. I’ll be talking about that in my article, too.

  2. Pepe Guerrero

    I combine both types of elements, dependats I to want view, for example, Caldwell 14 (Perseus´s double cluster), I see best with my 10X50 binocular (5 degree FOV), than my Meade DS-2090 Telescope with Celestron 32mm ploss eyepiece (2 degree FOV). But when I want to view Theta Orionis, I prefered my telescope. Greetings of Pepe Guerrero of Aguascalientes City, Mexico.

  3. Guy Babineau

    This is an interesting comparison. But the starblast and the 70 mm binos may be pretty close in light gathering surface area. I don’t know what percent obstruction is imposed by the starblast’s secondary but in terms of light collection surface area, doesn’t a 114 mm mirror have only 33% more area than two 70 mm lenses? If the secondary mirror obstruction is 20% there isn’t much difference.

    Could any of the remaining differences be explained by the quality of the mirror and lenses in either system? At the price of those binoculars, I would expect some pretty fantastic optics whereas the starblast represents value. How would a quality 100mm APO compare? Would that have a closer light collecting surface area and similar optical quality?

    I read this with interest because I like my 10x50s but would like something between that and my 16″ dobsonian that is easily transported in my airline luggage. I am leaning towards another pair of binoculars rather than a small scope for the same reasons you observe.


  4. Tony Flanders

    Actually, I’ sure that the Starblast’s primary mirror has far better optical quality than the objective lenses of the Fujinons. It has to, because it’s designed to run at 100X or higher. Flaws that would be obvious at that magnification are utterly undectable at 16X. As for something portable but more powerful than 10×50 binoculars, remember that the scope is far more useful for high-power viewing, not only of planets but also most deep-sky objects. In any case, the portability will be limited primarily by the mount, not the instrument itself. At low power, a Starblast is closely comparable to a 100-mm APO refractor. Obviously, the APO pulls far ahead at high magnification, though.

  5. Bob Peterson

    No question about the capabilities of big binocs. The big problem is being able to use them for more than a short time.
    Go to to see Sim’s ‘couch potato’ binocular chair or look in Amateur Astronomy # 63 for my mod to Sim’s design. Comfort when holding big binocs is the keyword!

  6. Bob Peterson

    Oops!!!! I should have talked to Sim first. He had a bit of a problem with his E-mail address.
    Google ‘couch potato telescope’ . There are severtal pages describing more than one version of the chair.
    If you want to reach Sim Picheloup, the originator(?) of the design: 281-531-8813

  7. John Mahony


    The secondary obstruction in the reflector might be 20% (probably somewhat more actually- maybe 30% in a small scope), but that would be by diameter. By area, you’d have to square .20 (or .30), so it’s only a few % by area.

    But the reflector uses two mirrors with reflectivity about 90% each, so the light loss is significantly more than the (refractor) binoculars, even with the extra prisms needed in the binos.

  8. Patrick Hopkins

    You might not be using the full aperture of the StarBlast. At 18X, the exit pupil would be about 6.3mm – many people’s dark-adapted pupils are smaller than that. As you probably already know, if your pupil is smaller than 6.3mm, the effective aperture of your scope would be your pupil diameter time 18. And the central obstruction would then count as an even larger percentage.
    The 4.4mm exit pupil of the 16x70mm instruments easily fits within most people’s pupils.

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