While I usually use a loupe, I don't always. For initial focus, without the loupe, the Intenscreen is best viewed head-on--so much so, that with your eyes close to the screen the distance between your eyes (parallax) lessens the brightening effect. As you move away from the screen the parallax decreases and the brightness becomes more apparent. When using the loupe, you only use one eye, so this becomes moot. On the other hand, when using a loupe, the increased brightness is much less apparent and I doubt if you could appreciate 2 stops of brightness, let alone the advertised 4 stops. You might do just as well with a higher quality precision ground glass.
Originally Posted by bmac