I can't figure out the relationship between the display size, the frequency in perlin noise plug ver 1 and the center point on where I am zooming.
Think of the Perlin noise as a scene with unlimited resolution. The scene is created by octave, frequency and seed. If you keep those values and only change width and height, you change the resolution, thus zooming in or out. Width will change the horizontal zoom, height the vertical.
Let's say, perlin was set to 64x64. If you now change it to 128x128, you see the same scene, just with more detail. If you keep the output size at 64x64 (e.g. drawing in a canvas), you effectively zoomed in. To still present the center, you wouldn't draw 0 to 63, but 32 to 95. You calculate that like so:
1x zoom was presented with a 64x64 perlin, area shown was 64, center is at 32
2x zoom is presented with a 128x128 perlin, area shown still is 64, center is 64. Half of the area is 32, ergo 64 - 32 is the left/top-edge, 64 + 32 - 1 is the right/bottom-edge.
Here's a very rough example cap:
perlinzoom.cap
(I wish English was my native language, I could explain it so much more understandable)