Recently I have heard of difficulties with optical quality differences between the right and left barrels of the APM 150 ED binoculars, with the right barrel generally said to be of inferior quality to the left.
Today I decided to take a critical daylight look with my copy of the 150 ED to see if I could discern any differences between barrels.
Four different eyepiece pairs were tried; the 30mm 2" APM UFF; the Docter 1.25" 12.5mm; the Baader Morpheus 1.25" 9mm; and the Baader Morpheus 1.25" 6.5mm.
Weather was almost completely calm with what I would call "cloudy-bright" skies. No direct sunlight was striking the ground between the instrument and the target during this observation.
The target was about 9.5 miles distant, and consisted of a small dead tree standing on a rocky scree slope that was uniformly covered with snow, providing a pure white background for the dead tree, which had two trunks with several dead branches extending from each side of the close-together trunks.
My goal was to see whether I could count more branches with one barrel or the other, and to see which eyepiece set performed best for this target on this particular day.
The APM 30mm UFFs just did not provide enough magnification, (28X) to compete with the other eyepieces tried. Strangely, when I tried the 30mm's, atmospheric instability, (seeing) seemed to be worse. The waves of atmospheric distortion seemed larger and more damaging to the image than with any of the other pairs, except maybe the Morpheus 6.5's.
The Docter 12.5's gave the most comfortable views and scored the highest on number of small branches visible. With this pair I could see 8 small branches extending off the left side of the left hand tree trunk, through the left barrel of the BT, and the same number through the right barrel. Any difference in image quality between barrels was indiscernible to my eyes. Both were equally bright, sharp, and showed equal and correct colors.
The Morpheus 9mm's were second to the Docter's, allowing a count of 6 of the 8 branches seen with the Docter eyepieces, to be seen with each barrel, and also with both barrels combined. Atmospheric turbulence seemed to detract from, and soften the images more than with the Docter's, which was expected at 93X vs 67X magnification.
The Morpheus 6.5mm's, at 129X, suffered the most from atmospheric turbulence. Only 4 of the protruding branches seen with the other eyepieces could be seen with the 6.5's. Images were even softer than with the 9mm's, as expected.
For all eyepiece pairs, using both barrels at once improved the image sharpness and apparent brightness plus seemed more comfortable, but in no case were any more branches visible than when using one barrel at a time. This was true for all four eyepiece pairs used. The sharpness, brightness and comfort improvements were expected, but I was surprised that using both eyes, (and barrels), didn't in any case increase the count of branches seen with a particular eyepiece pair.
At times I noticed a slight amount of brownish green CA near the field stops, but this was present with all eyepiece pairs, and not surprising with the very bright white snow background contrasting with the black field stops. No CA was noticed around the dark branches or trunks of the dead tree.
The less than stellar seeing quality today was somewhat surprising. The wind was relatively calm and the air temperature should have been fairly uniform. Outdoor temperature here on the valley floor was about 38 degrees F, with little or no sun shining on the ground. Apparently enough energy from the sun was getting through the clouds to heat the ground enough to cause turbulence in the air, and thus the wiggly seeing. The wiggles appeared as very small waves at a very high frequency of occurrence. Through the 12.5mm eyepieces this appeared like a "grainy vibration" in the air. With the increasing power of the 9mm and 6.5mm eyepieces, the graininess appeared more and more like small high frequency waves of distortion. The 30mm eyepieces were used last, just to see if they would clean up the poor seeing and provide a sharper view, but surprisingly they did not. Through them, the atmosphere appeared more like on a sunny day, with rather large and lower frequency waves visible. I believe this is due to further deterioration of atmospheric stability as the afternoon progressed, rather than any problem with the eyepieces, as at 28X, this APM pair is generally superb for clarity and sharpness.
I was never able to discern any reliable, definable difference between the right and left barrels. Rarely, when trying to focus precisely, I thought it was a bit easier with the right barrel, but this could have easily been due to my imperfect eyesight, or even the fact that I'm right-handed, allowing better manual dexterity with the right focuser.
At least with my copy of the APM 150 ED, I'm convinced that the right barrel is no different than the left, for all practical purposes, on a "cloudy bright" day and viewing this kind of terrestrial target.