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Message: <blockquote data-quote="Binastro" data-source="post: 3266160" data-attributes="member: 111403">. Firstly, the Helios 8×21 pocket spy monocular seems to have been discontinued a few years ago. I think I paid £13.95 when I got mine.I tested it this morning at 6 AM and just now at 2 PM against the 10x25 Docter roof prism binocular.The 8×21 monocular acquitted itself well. The image scale is of course smaller. The real field of view, which is marked as 6.5° seems accurate and is a bit larger than the 10×25.I could not detect any chromatic aberration with the 8×21 looking at a white pillar. There was a small amount of chromatic aberration with the 10x25 binocular.. There is a small amount of pincushion distortion with the 8×21.I have little accommodation and the sharp view is about 50% of the field. It is not symmetrical about the centre field. In use I have never had a problem with sharpness.I use this 8×21 monocular to identify things that cannot be identified with the unaided eyes. I leave the focus near to infinity. Usually these UFOs turn out to be balloons, sometimes with very strange shapes. Sometimes they are kites. I also use the monocular to read road signs at a distance and to see what is in the charity shop window without crossing a busy road.I would endorse the 8×21 Docter monocular, even though I have never seen it, as I know their products are good.However, I would query whether any of these small folding monoculars are viable instruments for use for long periods. Even holding both my hands together there is considerable movement. At least with the 10×25 binocular I can brace it against a lamppost or a tree or something else.The 8×21 that I have is in very good condition despite having been used many times. Some of the printed numerals are beginning to wear off from use. And the surfaces that contact each other when you fold the monocular for use show signs of use. Also, very importantly, when you fold the monocular for use the angle is exactly 90°. With a 5×25 folding Russian monocular, this does not happen as it folds by about 93°. So I have had to scratch two marks in the red paint so I can in line the monocular at exactly 90°. Although this 5 x 25 is larger than the 8×21 it can be held very steadily, being only five times magnification.One problem I had when testing the 8×21 pocket spy was that the eyepiece focusing was very stiff. This is because I have not used the focuser much. After using the focus a few times it freed up quite well, but I'm not sure it could be used for accurate focus in say one or two seconds. Maybe the Docter 8×21 is better in this respect.I see that they are selling 8×21 folding monoculars for less than eight dollars. I think these are very cheap knockoffs that seem to fall to pieces. One can always make something cheaper and nastier, which seems to be happening everywhere nowadays, especially with some Chinese goods, especially the fakes.I have used the pocket spy on numerous occasions and it takes little room in one's pocket. However, nowadays I keep the 10x25 Docter binocular in my pocket as it is a very useful and high quality instrument, which can be used for long periods if necessary.</blockquote>

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