[megaprogman]

So in my group last night, we had a bit of a debate.  So we believe that the rules state that if you use natural image magnification (such as a refracting lens), then you can use that to cast line of sight spells.

Does this mean a mage, on a mountain top, with a refracting telescope looking down at a city could be a "spell sniper" and cast spells at extreme distances?

[Stainless Steel Devil Rat]

So in my group last night, we had a bit of a debate.  So we believe that the rules state that if you use natural image magnification (such as a refracting lens), then you can use that to cast line of sight spells.

Does this mean a mage, on a mountain top, with a refracting telescope looking down at a city could be a "spell sniper" and cast spells at extreme distances?

Potentially, yes.  There's nothing stopping the GM from imposing a penalty based on that situation though.  For example, the refraction of the light through the intervening air at that extreme distance could plausibly impose some sort of "visibility" penalty even though spells don't normally suffer them.

Regardless, it can be something of a challenge-to-impossible to erase your tattletale astral signature after your spell snipe via telescope.

[Sphinx]

As a house rule, we use sniper rifle ranges for spellcasting, since they're the longest intervals (Range Table, SR5 p.185). Normal environmental modifiers for visibility, light conditions, and range apply (Environmental Modifiers Table, SR5 p.175), and you can reduce the range penalty by one category with optical magnification (Environmental Compensation Table, SR5 p.175).

[Stainless Steel Devil Rat]

As a point for players who insist on taking things to absurd lengths:  No, you can't astrally snipe targets on the moon (or even in LEO).  Even assuming you could get good enough magnification & stabilization to clearly see a metahuman sized target at those distances, there's no astral space in space. 

[Kiirnodel]

Actually, "Spellcasting by visual targeting is subject to normal visibility modifiers."

That's from page 281 of the Core Rulebook, in the entry for targetting spells.

The problem is that standard Perception doesn't have a guideline for the distance modifiers. Distance is one of the standard Visibility penalties so it really should have one...