Telescope Reviews: Are 7x50's any good at anything?

Several weeks ago, I realized that I needed a good 7x50 binocular to make my own opinion about this question. I choose the 7x50 Kunming Series 8. The brand is APM, but it's the same bino as the WO 7x50 ED, the Telescope Service 7x50, etc... I can confirm that it's an excellent binocular, with very good coatings. (It's really strange that the same Chinese manufacturer can produce the 22x85 that I tried, and that was a pure horror in comparison ! But that's not the subject).

Before relating my findings, I must add that I have measured my exit pupil between 6 and 6.5 mm, I generally use my binoculars on a tripod, and I can easily move at a dark site where the SQM reaches 21.55.

The first surprise was the exceptional sharpness of this binocular. I compared on the same stars the APM 7x50 to the Nikon SE 12x50, which gives anything but soft images, and discovered that the 7x50 provided a slightly better pinpoint aspect of stars. This proves to me that the Nikon 12x50 could be better if its optical aberration were reduced, or put in another way, that the low magnification of 7x50 binoculars is forgiving for common optical deficiencies of binoculars.

The second surprise was the difficulty in eye placement. For me this binocular is rather uncomfortable, whether I use it for daytime or for astronomy. I discovered that the eye relief was too long for me. I measured the usable eye relief, with folded down eyecups, and found 20 mm. But even if I manage to put my eyes at the right distance from the eyepieces, I still find lateral positioning of the eye to be somewhat critical for astronomy. I prefer in this respect small exit pupils, no larger than 4 mm, because the eye placement appears intuitive in this case.

About performance, the difference between the 7x50 and the 12x50 is really huge. While the 12x50 shows an interesting variety of aspects among deep sky objects, the 7x50 desperately shows many of them as fuzzy spots. Of course, this is not a discovery. But moving at a dark site changes nothing, contrary to my expectations. The 12x50 still outperforms the 7x50 by a large margin, on any kind of object. I have tried difficult targets, like the Helix nebula, the Pleiades nebula, the Veil nebula, the structures of the Milky Way, dark clouds, and every time the 12x50 was better. For example, some parts of the Milky Way appear rather uniform in the 7x50, but I can see a lot of complex structures in the 12x50. Some dark clouds are obvious in the 12x50, and almost invisible in the 7x50 !

Then, I made cardboard rings to stop down the 7x50 to a 7x28 binocular. And guess what ? I think I prefer the 7x28 configuration ! The faint dark clouds and subtle brightness variations of the Milky Way become more visible for me with a 4 mm exit pupil. When I remove the cardboard stops, the image is noticeably brighter, but appears washed out. A 7x35 configuration gives me a pleasing image too…
This result defies logic, and I would not have believed it without my experiment. I have no explanation for it.

Jean-Charles