Variable Neutral Density filters - anyone here ever used one?
I saw this filter and I was wondering if anyone here had ever used one and how well they work...
Sounds like a double polarising filter.
It is similar to having two polarizing filters and rotating one. Alternately, look at an LCD monitor or LCD TV through the lens of a pair of polarized sunglasses, then start to rotate the lens - same principle. You could also look at the screen with a camera's polarizing filter. (An LCD screen has a polarized filter. When the liquid crystals line-up in a certain orientation to the filter, they block the light, causing the image you see on your LCD. This works with any LCD display, even watches.)
I bought a cheap variable ND filter to tape on the front of a pinhole camera I made from a cigarillo box, wanting long exposures. I first put it on my 35mm while pointing at a flat light source, rotated the lens, and watched the in-camera meter. This way I was able to get an _approximate_ idea of how much light-reduction I had at each marking on the filter-ring.
Seeing that I'm new to pinhole cameras, I can't really comment on how well it worked. It gave me what I wanted, though. I have used it on my 35mm a few times and it seemed okay, but I'm not the best photographer, so what is acceptable to me may not be to others.
Those others can tell you if a variable ND filter will degrade your photos compared to a "static" ND filter.
No answer to the question, but buying another polarizer (preferably of the same qality as the the first one) will get you there too, though slightly a bit more clumsy as both filter are able to rotate, unless one is locked somehow.
I was given a no-name 77mm version of same, and have experimented with it a little bit. It isn't fully "calibrated" yet, so I don't have any good examples to show.
Originally Posted by TheFlyingCamera
They are available at a number of different price points, from incredibly cheap to really expensive.
The cheap ones are vulnerable to being uneven in their effect.
“Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”
Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2
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Just a word of caution about buying a cheap one and/or just sticking two CPLs together back-to-back (or is it front-to-front?). At very-low and very-high filter factors, you can get a colour cast, I've tried building my own and managed to get it at a point of the whole shot going rather green or rather purple. Even with digital that's useless, I'd hate to try to remove a colour cast from film. Also, you can get a cross-hatching effect in certain circumstances.
I'm all for saving money on a lot of things (and very often do), but with vari-NDs more than anything you really do get what you pay for. I've never heard a bad word said about Singh-Ray or Heliopans (except the price, see here for a simple comparison, Singh-Rays and Heliopans are 10x the price of the cheapest Vivitar/Polaroids).
An awful lot of electrons were terribly inconvenienced in the making of this post.
I know of polarizers that got a colour cast. But that colour cast only at low and high densities you describe puzzles me.
Originally Posted by Dr Croubie
A photographer once showed me some wonderful 10" X 8" colour transparencies taken with a polarising filter and rule number one, don't buy a cheap version. You get what you pay for.
“The contemplation of things as they are, without error or confusion, without substitution or imposture, is in itself a nobler thing than a whole harvest of invention”
I for one advise against them... I myself bought a cheap one off of ebay in order to increase my exposure by the most i could. The reason i went for one of these is, i ended up reading that even high end ones tend to give you that 'cross' (cross hatch?) look, although some have a stopping mechanism so that you can't fully rotate them (as the cheap ones do) and so you don't ever notice when it starts or stops. The cheap ones do degrade the image noticeably, and i fear i'm sure the expensive ones do as well, perhaps to a lesser extent.
I recommend only using 'single density' nd filters as they are many times better.
I ended up getting (again from ebay, reading reviews this time) an equivalent 10 stop filter, which actually does the job. For black and white it is great! Unfortunately, doing my exposures for several minutes i don't calculate reciprocity failure very well, nevertheless, it has been very fun to use it, especially the times it did work. I went for the 77mm as it fits my mamiya lenses as well.
If you are to use one with color i would be careful with color casts (as a user of dig*tal i can fix this specific filter with large amounts of white balance, but for film, i can't imagine the work it would take).
I've been looking at these recently - there are some Polaroid branded ones going cheap on eBay. I've not tried one though and I think I'll just buy an Haida ND3.0-II (1000x) for long exposures.
Putting a pair of polarisers front-to-front is HORRIBLE, even ignoring the mechanical craziness needed with reversing rings and stuff. Once you get past about 6 stops, you get very dense and uneven colour casts with funny patterns in them. I'm not sure, but I suspect the problem is the presence of the quarter-wave plate on the input (what was the back of a circular polariser) side. Their effect, being to introduce a 90-degree phase lag in one axis with respect to the other and thereby convert linear to circular polarisation, is strongly wavelength-dependent. A commercial vari-ND would have to be far, far better than combining polarisers manually, even if that's how they work internally.