What I have learned is that, at the darker settings, there can be a significant amount of IR pollution that can produce severe (and virtually impossible to remove) lens color cast. One should either put an IR cut filter in front or buy the newer variable ND filters with IR cut coating built in. From B&H http://www.bhphotovideo.com/indepth/photography/buying-guides/hdslr-guide-chapter-4-filters One important thing to be cautious of when using ND filters is infrared (IR) light pollution. ND filters cut down visible light, but don't cut down light in the infrared spectrum. With each stage of ND filter, IR light transmission is increased, causing desaturated colors and low contrast images. This issue is most noticeable in a scene with a lot of green, like grass and trees—the green colors shift toward the reds and become more of a muddy brown. IR pollution complicates things in post production and limits the color-grading process for HDSLRs. In order to combat this issue, filters that cut down on IR need to be utilized when heavy ND filters are used. The main options for cutting down IR pollution are the use of a separate IR filter in front of the other filters (only one should be used), or the use of ND filters that include an IR blocking layer. The latter is ideal because it results in less glass in front of the lens. Bob Sent from my iPad On Mar 20, 2013, at 7:05 AM, David Young <dsy@xxxxxxxxxxxxxxx> wrote: > Xavier! > > I hit "send" to soon. In another review of the SRB VD filter, they say; > >> A variable ND is two sheets of polarising filter mounted in a filter >> ring. The front sheet rotates and the rear stays still and by turning >> you reduce light transmission. Considering all this, the filter is >> surprisingly slim and only weighs 40g. > > This confirms my theory of how they are made and work. However, the > illumination test in the review shows that there are some substantial > differences in evenness. > > See: http://tinyurl.com/d7u6m9g > > The unevenness of exposure, especially when at the darkest settings, makes me > wonder about the wisdom of the idea, as opposed to some stacked, standard ND > filters, which may have some distortion (in lower priced units) but at least > the illumination should be even. > > Still, at the low cost, one might be worth a try! > > David. > > ------------------------------------------- >> Dear Flexers >> >> On Fleabay, I've come across a product named 'Fader ND2 ND400' >> >> It's obviously a filter made of two parts rotating with each other such >> as a a Polarizing filter. >> >> This Fader has a scale and an index to match the scale, every mark does >> a ND ponderation. >> >> Who has tried it, any good? >> >> Thanks for the input. >> >> >> #----------------------------------- >> From : Xavier F. BILLE >> mail : hot_billexf@xxxxxxxxxxx >> Maisons Alfort - France > ------ > Unsubscribe or change to/from Digest Mode at: > http://www.lrflex.furnfeather.net/ > Archives are at: > //www.freelists.org/archives/leicareflex/