I finally cracked and decided my eyeballs were not up to SMD work, and holding a magnifying glass was just too clumsy, so yet another bit of kit has appeared. 7x to 45x binocular microscope from AmScope. Very nice working distance and excellent clarity, at full zoom an 0805 resistor looks like a house-brick. FOV at 45x is about 4mm. At 7x zoom, full frame is about 25mm diameter, with 100mm working distance.