Chinese 25x100 45 Degree Eyepieces

Mfr: China Youtai Optical Instruments Factory, Kungming, China.  Web site of marketing firm.

Serial Number: FJ000026

Date: 2001

AFOV: ~63 degrees

TFOV: ~2.5 degrees

Eye Relief: ~14mm

Prisms: high index Porro II and roof

This Chinese made 25x100 binocular with eyepieces angled at 45 degrees is a descendant of a military model with straight through selectable 25x and 40x eyepieces (similar to earlier Zeiss binoculars).  This model has only a single set of eyepieces and also comes in a 40x version.  The eyepieces have fold-down rubber eyecups but I found their shape to be poor (contoured eyecups would be better).   The individual focusing eyepieces are mounted on Porro II prism housings (see picture above of the prisms) which rotate to change the interpupillary distance.  To achieve the 45 degree angle, Schmidt roof prisms are probably used but I have not disassembled the unit that far to confirm this.  The optics are said to be multicoated but the reflections off the coatings on my sample are relatively bright and not of the highest efficiency.  Later versions are supposed to have improved coatings.

The appearance and build quality of the Chinese 25x100 binocular is quite good.  The body has an attractive silver finish, though it is slippery to hold.  A handle would be useful and has been added to later versions.  The binocular came with a sturdy wooden tripod and a barely adequate tripod adapter with altitude control.  This altitude control does not allow enough travel towards the zenith but an improved adapter is supposed to be available from the American distributor.  My unit also came with a protective hard case with wheels that is usable, but not nearly the quality of something like a Pelican case.

As for optical performance, the 25x100 offers moderately wide angle views with fairly good performance.  The eyepieces are Erfle type (2-1-2, see picture above) with the typical softness towards the very edge and some pincushion distortion.  Some lateral color is also visible but I did not find it objectionable.  My main complaint about the eyepieces is that they do not have enough eye relief to see the full field using glasses.  I did find them comfortable to use without glasses (but users with a large amount of nearsightedness may find there is not enough adjustment to reach infinity focus).  I did not have any problems with collimation on my sample.  Stars appear as pinpoints except close to the field edge.  I have heard reports of variable quality control on this and similar Chinese models.

Overall, I found the Chinese 25x100 to be a very good value considering its price (around $1500).