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Maximum utility/durability with minimum size/weight, consider Leupold.

VX-6 1-6x24 - CMR2 reticle is nice, glass is very good

Mk6 1-6x - a few more ounces and twice the price as VX-6 but FFP...

Harbor Freight has a solar fountain pump, but I don't think it's anywhere the size you want. It's a good fit for a goldfish bowl, but it's <$100

For advise, you need to describe the waterfall,...