Who is responsible for my neighbors privacy?

Using binoculars is IMO where  you crossed the line.

It's not odd that you will look up if you notice some kind of movement in front of you. You could say, if she would be sure not to be seen naked inside her private home she should have curtains closed. On the other hand, if you from now on keep staring at her window in hopes catching her naked it would be kind of intruding her privacy, but not as it's described in your question. My opinion.

Hey hunny,  if you're gonna be prancing around in your birthday suit with the curtains open?  Then don't complain when I take a peek at your naughty bits. This post was edited by Benedict Arnold at October 31, 2016 1:38 PM MDT

If she was going to walk around naked she should have closed her curtains. 
At the same time you should not purposely look/stare into the house windows.

Since we live in a societal community, everyone has obligations to this effect.   I am responsible not to overstep my boundaries when it comes to invading another's space and they are responsible not to provide an attractive nusance (or unattractive as the case may be)

Your neighbours are responsible for their own privacy, excon, and you are responsible for your own. If you can see into each other's houses, it's best to close the curtains to maintain privacy. I don't like my own privacy invaded and I don't like to invade other people's privacy if I can possibly help it, and that is why I prefer to close the curtains myself.

I think that if a person is in plain view then they should expect to be seen. She made the choice to be naked near a window. It would be different if the nudity or exposure was not by intent such as a woman was wearing a light shirt and was splashed by water on a dry day.

I think she meant for herself to be noticed in all her bare skin. For some people this is kind of exciting -the exhibitionist- but not likely interested in being approached by any person. 

My best view one time was walking in the alley early morning when a movement in a window caught my eye there was a young lady just pulling up her panties.  Good timing! This post was edited by Kittigate at October 31, 2016 9:54 AM MDT

There's actually a chance she could be cited for indecent exposure for something like this. While people are entitled to a reasonable expectation of privacy in their homes, that tends to end when there's a clear view from another home or the street. If she had a fenced off backyard and found people climbing the fence, looking through the slats, and things of that nature, they would be in the wrong. You, on the other hand, wouldn't be in trouble for something you could see from your patio or driveway. 

Ethically, rather than legally, I still think you're in the clear. If you aren't seeking it out, what else can you do? Anyone else would have responded the same way.

Depends,  I tend to walk around my house with little on, as soon as I walk in I strip down to my panties, if I'm not wearing panties I will put on some lightweight short and if others happen to see me, so be it.  I have pretty much always have since I was a child and I do it for my comfort, not to stimulate others.  If others want to look, I'm not going to run and hide, unless they taking it to that next step.    The law if fairly clear in this regards in most states, a person has the right to be naked in and on their own property as long as it is not being done for self gratification or the gratification of others.   If you were my neighbor and saw me you would have every right to look, now if you have to climb a ladder to see me...or peer in my window to get a better look, then you have now crossed that line.  If I saw you looking and I started doing things to entice you even more and to turn you on then I have crossed the line.      

I suspect she can walk around naked as much as she wants. If her motion caught my eye I think I would have glanced and probably done a double take or perhaps a triple take. After that well...I don't know.....

From a legal standpoint she is not supposed to expose herself.  If she is visible, naked, inside or outside of her house and you see her, that is indecent exposure.