How far away should I be from my subject in order to avoid perspective distortion?

Could you explain how it is done?

I have a DX Nikon camera. If I shoot with a 25mm, 50mm, and 85mm lens then how far should I be from the human in order to avoid this factor?

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Nikon 7246 12x50 EX Extreme Action compared to Nikon Action 16x50 EX?

I want to buy a nice binocular and confused between:
Nikon 7246 12x50 EX Extreme Action compared to Nikon Action 16x50 EX

In stores both are not available, I have to order online so without using its difficult to decide.

Any answers please?

Read more: Nikon 7246 12x50 EX Extreme Action compared to Nikon Action 16x50 EX?