Horukuru,
Henry sort of answered your question, but let me try also. The practical limit for daytime viewing for a scope that is very well made and has very low aberrations is around 1x/mm of aperture, so 60x for a 60 mm scope and 95x for a 95 mm scope. But there are diminishing returns already well before that magnification is reached, and some marginal extra resolution available above that, so it is a rule of thumb. In practice, having used a very high-quality 82 mm scope with 75x maximum magnification, I think it was very seldom that I would have benefited from more magnification in that scope for daytime views. But, there were lots of times I did use that 75x and would have been sorry not to be able to. A magnification corresponding to that in a 95 mm scope is about 87x, and for the ATX which is a bit brighter than the Nikon I used before, I would round that number up to 90x. If and when you use the scope also for enjoying the night sky, much higher magnifications would be good to have, but that is a secondary consideration with these scopes.
But really, it is a matter of compromise, especially if and when you only offer one eyepiece, like Swaro has done. For the 2.4x zoom ratio the ATX prism module has, the 30-72x range is a sensible compromise. 2.4x is doable if one requires not unreasonable size, very wide fields throughout the zoom range and a field that is sharp to the edge. If the scope instead had a zoom like the Meopta 20-70x zoom, which is not a wide-angle but has good eye-relief and is also sharp to the edge at all magnifications, one could have a range of 25-87.5x, which would cover almost all needs.
Kimmo
