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Cold night notes, Fuji16x70, Ober15x70, Ober20x80

Started by EdZ, 01/13/2003 01:22PM
Posted 01/13/2003 01:22PM Opening Post
I had several pair of binoculars out back this weekend, all mounted. Included were Oberwerk 15x70, Oberwerk 20x80 and Fujinon 16x70. Some tests between these three revealed the relative ability to see. Skies were noted as 5.0 mag. And some important cold weather info is noted.

Resolution notes: For wide, open clusters, I carefully pick outline boundaries and count stars within to see how deep binocs can see. On the Christmas Tree cluster, NGC 2264, both the Oberwerks see 17*, the Fujinon see 19*. On M44, 15x70s see 71*, 20x80s see 73*, the Fujinon 16x70s see 80*. Several other clusters produced similar results.

On small dense clusters that often just look like a glow in binoculars, I saw a real difference. The Fujinons contrast and resolution made it easier to discern stars within the glow of tight clusters. On M36, Ob15x70 saw 4*, Ob20x80 saw 4*, Fuji16x70 saw 8*. On M37, the 15x70s saw 3* while the Fujinon 16x70s saw 8*.

The Fujinon can be focused to a finer point of light than either of the Oberwerks. The Fujinon contrast and resolution makes it easier to pick out the fainter stars and pick out the stars embedded in the glow of many in the small tight clusters.

Although all the binocs could see the Pinwheel, the contrast in the Fujinons made it much easier to see the faint diffuse light of M33. Last week, using the Fujinons, I found M31 in daylight about 30min before darkness. Saturn’s rings are separated from the disk in all three binocs. The Trapezium is resolved to 3 stars in all three binocs. A-B at 8.7” is not resolved, but several times did appear elongated in the Ob20x80 and the Fuj16x70.

Cold weather notes:
I viewed for about an hour or two on Saturday night. I left the binocs out over-night so the equipment would be set up for a 5AM session. Temperature in the evening was in low/mid 20s, by morning temp was 18°.

The Fujinons were exactly as I left them, focused and ready to go. Both the Oberwerks changed focus, had to be refocused. I did gain additional diopter range on the 80's, which I usually have at the max minus even with my glasses on. Didn't need them at max minus in the morning.

The Oberwerk 20x80 became nearly impossible to move the focus dial.

The Oberwerk 20x80s changed collimation. They were out by morning.
Could it be the mass and length of the steel barrles has such a coefficient of expansion that the 20x80s literally changed shape overnight?


Posted 01/13/2003 05:04PM #1
I'm not surprisd by your results; Fujinon makes a quality product. I am, however, impressed by your fortitude. Eighteen degrees is COLD when you are trying to do delicate work. My hat's off to you!


Walter Locke
"The Fearless Spectator"

There are 10^11 stars in the galaxy. That used to be a huge number. But it's only a hundred billion. It's less than the national deficit! We used to call them astronomical numbers. Now we should call them economical numbers.
Richard Feynman
US educator & physicist (1918 - 1988)

Posted 01/14/2003 06:07PM #2
Ed, Thank you for your detailed observing comparison. It clearly shows that there is more to the story than Mag times Aperture (or Aperture^0.5). Have you done field flatness comparisons on these three?

I hadn't even considered the possible effects of cold temperatures on binoculars, so that was informative too. The coldest I have been out this winter is 28F, and my fingers were too numb to even grasp a focuser smile

Clear Skies, Milt