Friday, August 20, 2010

Scope Review Comments

There's a spotting scope review in the October 2010 issue of Birder's World magazine begging for critical comment. While there were some eyebrow raisers, I was baffled at scores earned by the Vixen Geoma II 82 ED, especially in the context of its closest competitors: Zeiss Diascope 85, Vortex Razor 85 HD, and Pentax PF 80 ED. For image quality, the Vortex Razor (3.9) barely outscored the Vixen (3.8) and the Pentax (3.7), but the Zeiss beat these three with an image ranking of 4.3.

I recently conducted some digiscoping tests with the Zeiss, Vixen, and Vortex scopes (sorry Pentax, you're just too heavy). All photographs were taken with my Nikon Coolpix 8400 against a resolution chart at 35' illuminated by a CFL light bulb, which rendered a warm color tone. (Note: The Vixen's close focus is not 49' as stated in the review.) Before conducting the tests, I set the 8400's white balance by measuring it on a white surface under sunlight so that any color deviation would be detectable - no auto-white balance was used.

Camera only: whites warm due to CFL bulb illumination.

For the first test, scopes were set to their lowest magnification (20x) while the 8400 was set to manual mode using same shutter-speed, f setting, and maximum optical zoom. The 10-second self-timer was used to eliminate image blur when engaging the shutter. To the best of my digiscoping ability, I took 5 shots through each scope, re-focusing each time in effort to obtain the sharpest possible image:

Zeiss 85 (green-ish color tinge).
$2,999.99 with zoom eyepiece

Vortex Razor HD (lower contrast, correct "warm" color).
$1,599.99 with zoom eyepiece

Vixen Geoma II ED (more contrast loss, less sharp, CA, color tinge).
$959.00 with zoom eyepiece

The second test kept spotting scopes at 20x, but I changed the optical zoom to 1x to demonstrate how much field curvature each exhibited:

Zeiss 85 (field curvature & green-ish color tinge).

Vortex Razor (flat field, correct "warm" color).

Vixen Geoma II ED (slight field curvature, greenish tinge).

The above results are consistent with my past and present observations when viewing through these particular spotting scopes. I'll concede points of subjectivity and the fact that digital cameras exploit differences in optical quality some individuals are unable to detect. However, if the Vixen Geoma II is a 3.8, and the Zeiss a 4.3, I think the Vortex Razor deserves > 4.0!

Strangest of all is that they rated the Vixen scope above the Vortex in the overall ratings. Take it from an experienced digiscoper and someone who has been selling spotting scopes for over a decade, if you desire a scope with inferior optical quality, lower build quality, and lacks a comprehensive no-fault warranty, the Vixen Geoma II ED 82 is the scope for you!

All images © 2010 Mike McDowell

1 comment:

  1. Nice practical test and thanks for sharing the results.