You could go to a frame store and have a frame made to size, then staple a breathable fabric of your choice to the frame (try to choose a fabric that won't change colour because of the sunlight). Depending on what your landlord allows you to do structurally you can install a track or even just hooks to hang the frame. I did something similar a few years ago when I wanted a headboard for the bed in my rental space. The frame only wound up costing me around 30$ from my local frame store, and it was 5 feet by 4 feet.

Not sure what filter screens are but curtains on spring tension rods hemmed to allow air flow at bottom and of suitable sheerness to conceal your activities but admit daytime light would be the simple solution..

Curtains?

OK, this is an off-the-wall idea, but ...

In greenhouses in the olden days they used to whitewash the glass when it got too sunny/hot. Now they probably have some fancy-schmancy paint for the purpose, but a dilute water color would probably work fine, or that "snow" stuff you spray on windows at Christmas time.

Then when autumn comes, you can just scrape/wash the stuff off the glass.

Open the windows from the top, and get an adjustable sized screen to fill the opening. (You can buy these at nearly every hardware or home improvement store.) That will allow you to put cafe curtains or some type of bottom-to-top blind in the lower half of the window while still getting airflow.

In our attic (no ventilation or insulation) in the winter we use a sliding vent type screen to let air circulate. Like this...

http://www.ebay.com/itm/10-H-Window-Screen-With-Ventilator-Adjustable-21-W-to-37-W-AWS1207-/330834506493?pt=LH_DefaultDomain_0&hash=item4d0745f2fd

We used to use one in our bathroom, too, when we had neighbors right next door.

I'm guessing you might have Walmart in Canada? We bought ours there. In the spring summer time is best to find them. Or I would think any large hardware type store would have them.

Good luck!

Shutters or horizontal blinds will let the air flow and the angle you choose will also allow for privacy.

Curtains or shutters.

I've had to deal with the same issue in our bathroom which has a window in the shower (that we like to open for ventilation) and the neighbors window is directly across from it.

I spent a couple months researching for ideas. I found that large louvered indoor shutters are the best solution for the problem. Although potentially expensive, depending on size and quantity, they can be custom ordered to fit at Lowes or Home Depot. You'll want to install them on hinges or get the adjustable ones so you can open them during the day for natural light.

Here is an example - http://www.fashion4windows.com/images/plantation-shutters/woodlore-shutters.jpg

Maybe try this?

http://www.2jane.com/collections/window-film-by-emma-jeffs

Top to bottom shades so you can have the bottom half of your window covered for privacy and then move your window screen to the top and open the top window portion.

http://www.blinds.com/control/product/productID,8759?gtse=googpb-8759-pla-36809403506&width=46.00&height=46.00&test={keyword}-11863974866&gclid=CPOO3YaowLUCFYk7Mgod_n4AfQ

I've heard the idea of using speaker grill cloth, its like a spandex looking material but more breathable. Comes in various colors and is inexpensive. It would be cheap and simple to make a frame and stretch the material over.

http://www.speakerworks.com/speaker_grill_cloth_fabric_s/25.htm

Flip the screen to the top of your window. It's also good for the safety of kids and pets. When you open your windows now open the top half instead of the bottom half.

I use bamboo roll up shades. They are dense enough to block the view, but let air in through the bamboo slates.

We have used tension rods and rings with built-in clips at the half way point of several windows. They're hung with fabric panels (we used plain white cotton MS tea towels which like all Martha Stewart stuff, were deep discounted when she went to jail, so I bought a bunch on spec). You could use any fabric you like. The effect is like cafe curtains. The white fabric allows privacy but some light comes through. This project took all of five minutes to hang and was inexpensive. It looks tidy and inoffensive... was intended to be temporary, but has been okay enough that I've lived with them for a couple of years...

We have this same problem--and windows that are fixed and only open on the bottom half. We used a series of things.

First, we put up the sheerest window film we could find. Next, we hung wood blinds if we needed less light. (They have large slats to let a lot of air through too). Finally, I put up sheer curtains (MATILDA, from Ikea). In the summer when it's hot, I can open the window, everything is blocked from sight, but we still get the light we need, and the curtain blocks what ever is viewable from the window being open.

Hope this helps! I understand this problem well.

...I forgot to mention, we used the above method only for our bedroom, where we wanted the most privacy and which also is visible to a large apartment building behind ours. For the rest of the apartment, which is lined up with the one across the alley - windows and all, we didn't use window film, just wood blinds and sheer curtains.

I have a similar problem, except it's excessive light vs. ventilation.. Any kind of fabric will block considerable amounts of air, even if they are speaker grill cloth (which let sound and some air through). I've decided that wide bladed horizontal blinds are the only way to go to get light control without overheating.

I have southwest-facing windows and my top floor apartment gets very hot and sticky in the summer. My advice is to get sheer white curtains, which are lightweight enough to allow the air to flow freely through an open window, but shield the neighbours from being able to look into your place.

Also, consider adding a UV window film to your windowpanes (something like this: http://www.homedepot.ca/product/sun-control-window-film-light-neutral/931984). While the windows are closed, it will seriously reduce the amount of heat that enters the apartment -- not to mention letting you sit by the window without getting sunburned.

Having a similar issue and trying to determine if and how to fasten a trellis to outside wall since Im on the 1st floor. Or nice-looking lattice if I can find any. Then growing a speedy annual vine on it until I can get a perennial established such as Wisteria. In theory Ill have scent and flowers to screen out my neighbors while still letting in light and air in the summer. On higher floors you might try a window box and plant a living screen with or without a trellis.
Finally instead of window film in case you were thinking of using it there is a glass-frosting spray paint I just used on my bathroom window which so far is working out great. I got it at Michael's. It covered very evenly and opaquely. It smells though when you apply it and have to use acetone to remove it but so far I'm much happier with it than the window films that kept peeling off both the windows where I applied them.
Good luck!

Hi Julie,

I agree with Rachel Brooklyn. I had the same dilemma because I live in an apartment with a view of my neighbors windows too. We are also east facing so at 8:00am the whole apartment was like staring into a disco ball.
Problems: we rent so I needed something that I knew wouldn't damage the windows or leave thick residue.
2Jane was my solution. Emma Jeff's is a British designer and the use PVC free film which means they are Eco-friendly. I have the Anni in my bedroom (it looks like Burberry plaid) and Orba in my living room. I have gotten SO many compliments on both. My husband likes the Pixel that's in our kitchen.
They were easy to install. I only installed them on the bottom half of my windows so I could still see out the top, but I live on the top floor, so that may not be an option for you.

http://www.2jane.com/collections/window-film-by-emma-jeffs

Regarding open windows, my friend bought a piece of plexi that fits over the window just shy of last two open inches & covered it in the window film. Then i slid it into the two curtain tie-back hooks that were in the wall (I just installed them up instead of facing out)

I hope this helps.
Good luck!
Ekho

I had a very similar problem in that my windows provide ventilation and face a walkway by which people are always passing. There are blinds that I prefer to be open so as not to block sunlight. I hung two sets of sheers. One white set the remains fully extended in front and a second set red accent that is drawn back during the day and allowed to extend during the evenings for added privacy. At the local shop the whole set, which my friends find very pleasing, was less than fifty dollars.

Hope that helps, Good Luck!