N-4x – is quite strong neutral density filter that reduces light amount 4 times. It can be used to increase shutter speed if necessary (to blur motion, for example).
F-1734 is weak diopter that allows to extend field of few by 1-2%.
Y-1,4x – light-yellow. It enhances transmission of visual brightness proportion of blue, green and yellow objects for portrait shots under artificial light, for nature shots with large clouds on blue sky, and for any nature shots with short exposures at twilight.
UV-1x is colorless glass. It is used to reduce effect of ultraviolet light (in mountains), for lenses without multi-coating to shoot on b/w and especially on color film.
Y-2x – yellow. It is widely used for all sorts of nature shots to achieve correct transmission of visual brightness proportion of blue, green and yellow objects. It highlights clouds and increases contrast of shadows and distant objects. It also eliminates effect of haze.
Edited by David C Connolly, 01 May 2012 - 10:26 AM.