As Don stated, the field of view is narrow at low magnification setting. I have this zoom and it works very well. I have not noticed blackouts or kidney beaing. You may not need a barlow at the 7mm setting, as that may be high enough power. There is a good GSO 2.5x barlow in the classifieds at the moment. It's really 2.2x apparently, so get that one if you think you need it. Excellent reviews all around the Web on that one for the price. It's the Bintel 2.5x barlow being sold by Morton.
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