How to Hand-hold a Binocular
1. The Wrong Way
The best way is definitely not the "normal" way, with the hands on the prism housings. Although this initially feels comfortable, it is inherently unstable and tiring.
2. The "Triangular Arm Brace"
Hold the binocular with your first two fingers around the eyepieces and the other two fingers around the prism housing. Then raise the binocular to your eyes and place the first knuckle of your thumbs into the indentations on the outside of your eye sockets, so that your hands are held as if you were shielding your eyes from light from the side. Each arm is locked into a stable triangle with the head, neck and shoulder as the third "side", giving a relatively stable support for the binocular. The position of your thumbs keeps the eyepieces a fixed distance from your eyes. You cannot normally reach the focus wheel on centre-focus binoculars when you hold them this way, but you should not need to refocus during an observing session. This grip does feel unusual at first, but it is so superior to the "normal" way that it soon becomes second nature.
3. "The Rifle Sling"
If you want the most stability you can get with a medium sized hand-held binocular, use the "rifle sling" method. This is similar to the way one uses a sling for rifle-range shooting. Hold the binocular so that the strap loops down. Place both arms through the strap, so that it comes just above your elbows. Hold the binocular in the most comfortable way you can and brace it "solid" by pushing your elbows apart. It's a bit like getting into a medieval torture instrument, but it's very effective.
4. Double-handed Hold for Large Binoculars
You may sometimes wish to hand-hold a large binocular for short periods, and find that the balance of the binocular makes the "triangular arm brace" method unstable. Assuming your right eye is dominant, use the "triangular arm brace" with your right hand and hold the right objective barrel with your left hand. The left objective barrel is supported by your left wrist (you may wish to remove any bracelet or wristwatch first). For extra stability, combine this with the "rifle sling" method.
5. General Improvement of Stability
However you hold the binocular, image stability will be improved if you can support
all or part of yourself on something that is itself stable. This could be something like supporting an
elbow on a gate-post, supporting the binocular on an up-turned broom, leaning against a wall, sit-leaning on a table or the bonnet (hood) of a car,
or anything other ingenious method you can devise from what exists in your immediate
environment. Sitting or reclining is particularly useful, especially if you want to
observe anything more than about 50° high in the sky.
For larger binoculars and for better stability for all binoculars, the solution is to mount them. Various mounting methods are shown here.