quote:

Originally posted by sambarman338:
Ovny,
As said above, I too have myopia but I had not noticed the problem you mention. That diopter you refer to would appear to be what we call exit pupil, the bead of light you see, which should more or less correspond to the size of the pupil or centre, black bit of our eye. I have heard myopics' pupils may open wider than in people with ordinary eyesight, say 9mm rather than the 7mm or 8mm of ordinary mortals. However, it is the size of the objective (front lens) that governs this, not the power range.

The Leupold 3-9x40 has an objective diameter of 40mm, of course, which means in poor light you can wind up to 4.4x at least before the exit pupil shrinks below 9mm. (To calculate exit pupil, divide the objective lens diameter in mm by the magnification, hence 4x32 gives 8mm; 4x36 gives 9mm.)

It has been said that there is another factor called 'twilight value' where you may get better results selecting a higher power in bad light, even though you've passed the optimum relative luminosity. I can't remember how that one is calculated but maybe it's what makes you think the 6-18 Revenge is better. Binoculars, for instance, often have exit pupils smaller than optimum without being considered inadequate for twilight usage.

There are other brands of scope that may give you slightly bigger front lenses (like 50mm) but they are more prone to damage if you bump them, especially if they have bigger power multiples (like 3-12, or crazy ranges like 4-28x), which probably have longer, heavier erector tubes inside.

However, those big scopes you mentioned don't help with gathering light because they still only have front lenses of 40 and 44mm to cope with higher powers. The 4-12x40 will give no better low-end light than the 3-9x40 and the 6-18x44 never gives you more than a 7.7mm exit pupil - and it gets much worse above 6 power.

So, there are bigger and more expensive scopes that may give you more light but high magnification will not help your perceived need of bigger exit pupils. Maybe you should look for a 3-9 with a bigger front bell.

Cheers
- Paul

quote:

Originally posted by Norseman:

2 completely different scientific terms, sambarman338.