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Measurable performance specifications
What is the Strehl Ratio
Spot diagram
Longitudinal Plot - Chromatic aberration
Then (and only then) if the above is suitable - some of the more user friendly specs - what type and quality of Focus system (backlash, smoothness, adjustability, total travel, locking mechanism, gear ratio, ability to add electric focus control) rotator mechanism, balance point, dew shield design.
Trouble is - what do you know the real specs of the only really critically important issues are absent on just about every manufacturers spec sheet and replaced with superlatives and meaningless drivel !
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