First, I'll just point out to others that may be following along, your "Levels 1" layer is acting very much like a threshold adjustment layer acting on the noise layer immediately below, "Layer 5".
As an example of the real source of the problem, assume you change the viewing magnification from 100% down to 33.3%. When you do this, PS averages ~9 pixels (=3x3) to produce one pixel at the new magnification. This happens on every layer. Because the original noise pixels on Layer 5 are now averaged, these new pixels won't be distributed as widely in intensity as the original pixels -- more will be concentrated around mid-gray. Therefore, fewer will make it through your thresholding operation as one reduces the viewing magnification.
To verify this is indeed what is going on, simply view your image at a wide range of magnifications. You should see that at magnifications of 100% and any magnification above that, the number of "stars" that make it through your thresholding operation should hardly change. However, when you start to go significantly below 100% magnification, fewer stars should appear.
The fix is easy: bake in the number of stars that you want by generating a new "real" layer of stars (ie, not an adjustment layer) at 100%. Then, as you scale it up or down either in viewing magnification, or when turned into a jpg or a print of arbitrary size, the number of stars won't vary.
Pls. let me know how this works for you.
Cheers,
Tom
