Why Build One?
I have found binocular astronomy to be a lot of fun. It is a great test of observing skills, and can be a way to do some observing at times or places where a more involved set up of equipment is not possible.
In observing with binoculars I have found the experience much more rewarding if I can mount the binoculars. There are various methods of doing that, and I have played around with many of them. I came across the idea of a downward looking mount using mirrors and liked the idea of the comfort that looking down versus up would afford.
I found a source for inexpensive first surface mirrors on the net and decided to build a mount.
There seems to be a couple of popular approaches to this type of mount. One uses a large mirror on a tilting platform. The advantages of that design is that the binocular eyepiece remains in a static position. The disadvantage is that it requires a rather large mirror to make it work, and "large" in this case also means expensive.
The second approach involves tilting the mount and binoculars together, allowing the use of the smaller, less expensive mirror. That is the path I took.
The construction is quite simple. Most of the unit is constructed from 1x2" Maple. The main beam is made from multiple pieces of maple glued and screwed together (Most all of the screws are in from the backside and not visible in these photos). The downstalk joins the main beam at a 45 degree angle and is also 3 pieces, but the center piece extends up through the main beam and is secured by glue and screws. The binocular mounting stalk is a single piece glued and screwed between the outer pieces.
The mirror rests on a platform of plywood and is secured with multiple dabs of silicone adhesive. The platform is attached to the beam at a 45 degree angle by a short piece of maple that, like the bino mount stalk, is sandwiched between the outer pieces. It is secured in place by a 1/4" removable bolt that allows removal of the platform making it easier to store and pack.
The entire unit attaches to the tripod using 1/4" 20 threaded insert in the bottom of the downstalk. It attaches to a pan and tilt head providing the movement necessary to scan the skies.
Using the Mount - First Light
Out under the stars for first light, things did not go as smoothly as I had planned. My favorite Astro Binoculars are Fujinon 16x70's, so I mounted them up and anxiously moved into the eyepieces. My first view was a jumble of fuzzy elongated stars. Quick check of the focus, maybe a little better, but not even close to the tight pinpoint stars I was used to seeing with these binoculars. After some experimentation using different methods, including checking the binocular's collimation, I began to suspect that the mirror might not be optically "up to snuff". To check that theory I took off the 16x binoculars and mounted my Fuji 7x50's, and sure enough, the view was perfect. The mirror simply was not smooth enough to support the higher magnification of the 16x70's.
Since then I have mounted 10x binoculars and enjoyed a very nice view, but I believe that magnification is about the limit for this mirror. A few month's later I noticed that the supplier, (who was quite responsive and accommodating) has added some new products to his offering, mirrors rated to support higher magnifications (at a higher cost, as you would certainly reasonably expect).
Using the mount, I have found two points regarding tripod features that I consider essential for maximum enjoyment. First is a nice damped tripod head. A damped head makes scanning with the mount a real pleasure. The second essential feature is a tripod with an adjustable center post. Tilting the mount changes the eyepiece height. Having it mounted on an adjustable center post makes adjusting to the new eyepiece much easier.
One other point. Using this kind of mount where I live means having to deal with dew. As you might expect, the mirror can dew quickly on some of our Iowa summer nights. Be aware of this, fight it by covering the mirror when not in use, or the other favorite dew fighting tactics like blowers or maybe a heating system.....
Aiming the mount is a bit of a trick and takes some getting used to. I have recently been experimenting with a green laser pointer as an aiming device. Mounted parallel to the binocular's optical axis, when activated, the laser hits the mirror and points out the current center of the view. Much easier than trying to "eyeball" it.
I do enjoy using this mount. The downward look is quite comfortable for extended viewing. The mirror smoothness makes high magnifications impossible, so this is wide field, casual scanning - more of a "Type B" behavior. Just what the doctor ordered some nights when you feel like getting lost for a while.
For another great way to view with binoculars, see my page on my
©2005 Rod Nabholz