Swedpat
1. I use a Glanz 7x40 9.5* monocular sometimes for feeder watch. My feeders are nearly in the same plane. I have used a Helios AMD+ 8x32 7.5* in the field in the past. I have trained myself to use two-eyed viewing, and keep the non-monocular eye as far as possible open all the time. I am right hand and right eye dominant.
A report of the experience of a long term user of monoculars would be much more valuable than the report that I am able to supply. But specific reports by anybody seem to be rare on the Forum.
I agree with your comparison of monoculars and binoculars, and add to your list as follows:
2. Advantages of monocular:
* (In favourable circumstances of direction and quality of lighting) two-eyed viewing:
There is not usually a great concentration of birds locally or in my garden, so systematic study is not possible. But as far as I can tell the open eye retains peripheral sensitivity to fast movement even when the elected image to view is the monocular image.
It is possible as an exercise to overlay the magnified image through the monocular eye exactly over the image through the open eye. And the brain can more usefully also hold and present both images either at the same time, or alternately, when the two eyes view separate images: in the latter case one switches between images with a slight blink.
But the whole point of magnification is to assist the location and appreciation of a small image. When the trees are in leaf, or the direction and quality of lighting is not favourable, the option of also viewing through the open eye is not a great advantage of the monocular.
The potential advantage of a peripheral sensitivity of the open eye to fast movement outside the field of view of the monocular does however remain
* Compression of planes:
As follows below, 'Compression of planes' will usually count as a disadvantage of monoculars.
But when observing the interaction of birds at a busy time at the feeders, eg when a flock arrives, I find when using the Glanz 7x40 9.5* monocular that the combination of the compression of planes, a good depth of field, and a wide field of view makes it easier to follow activity, and is an important advantage.
My feeders are about 12 metres away from the house. By comparison in the circumastances a binocular might also afford the same 'fixed focus' wide angle view as the Glanz, but it would weigh up to twice as much, require the use of two hands, and not compress planes
3. Neutral:
* Spooking:
I haven't to date clarified which of my optics spook birds less. My local or garden birds just don't like being looked at at below a certain distance. I don't seek to tame them. I fear it is not too healthy for the birds where I live for them to be too trusting. But I would like to be able to watch them a little closer
4. Disadvantages of monocular:
* Reduced apparent image size:
The reasons for this I leave to the optics experts
* Compression of planes:
Inherent in a single ocular.
Probably more often in the birdwatching task confuses than clarifies the image that the brain has to appreciate and interpret
* One-eyed viewing:
According to the direction and quality of lighting, very often when using a monocular one must hold the non-monocular eye shut.
I certainly don't find this comfortable for long.
However to an important extent the discomfort can be overcome by two-eyed viewing.
I don't treat this above as an advantage of two-eyed viewing, because it is rather the removal of a disadvantage.
But part of training oneself to view two-eyed is to train oneself when concentrating upon the image through the monocular eye to disregard the image through the open eye.
* Two-handed holding:
Quite often, in order to steady the monocular, or to shield it from side light, one must use two hands.
In particular, as Bill Cook has pointed out, one way to steady an optic is to hold it by the far end of the barrel. If a monocular is steadied in this way, it then must be focussed by the free hand.
So one of the important advantages of the monocular over the binocular is lost.
Stephen
