Section 2 - F-ratio?

But the faster the focal ratio, the improved corrections of an air spaced lenses become are more and more significant. At F/7 focal ratio or above, there is very minimal difference between an oil spaced and an air spaced lens, so in this range we would choose an oil spaced lens without hesitation. But somewhere in the F/5.5 � F/6.5 range, the air spaced lenses start to dominate the market, and it is natural: here, their improved sphero-chromatism produces a visibly less amount of false color, and for their intended applications (e.g. wide field deep sky photography) this improvement is more important than the longer cooldown time, or their decreased ability to follow the temperature changes of nature.

For these reasons, we do not plan to produce lenses under about F/7.7 focal ratio, maybe the only exception is the planned 102/640 telescope, which will be especially designed for travelling. This scope is not intended to win the "most color free APO on the market" prize (though it will easily match the definition of practical apochromatism), our main goal with this scope is to make a travel telescope which is very small and portable, and makes it possible to fully utilize the (often limited) observing time of an amateur astronomer during travelling.

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