Aleks, I've just tried the very same thing., filters with pinhole. I used a deep red filter behind the pinhole to enhance the seperation of sky and clouds. It also had the added benefit of cutting through the industrial haze we sometimes get in the Northeast. But a word of warning, make sure the filter is absolutely perfectly clean and blemish free. The slightest mark will show up on the negative. I'll post the scans of my latest effort so you can see what I mean.