Fotodiox Pro 6.6"x8.5" filters are the strongest in the industry at 4mm thick. Fotodiox 6.6x8.5" filters are practically unbreakable and are guaranteed spectrally neutral to within + or – 3 in the a and b channels of the lab color space. This filter is made by Fotodiox Pro specifically for the WonderPana 66 & WonderPana FreeArc Filter Systems. Color graduated camera filters create an effect in the top half of your photo and leave the bottom half alone. They are most commonly used on skylines for landscape work. This hard-edged filter has a defined hard line transition, as opposed to the smooth transition from clear to color provided by the soft-edged type.