Cheap Vario Neutral Density filter

[NannyFerret]

A cheap Vario (£5.99) adjustable neutral density filter. bought off ebay.
I was just testing it very quickly and the shot was a bit under-exposed so some editing was needed as I couldn't go any slower with the shutter speed.
It was hand held and was a bit soft so re-sizing to smaller was needed as well.
It was basically to see how easy it was to use.
I also bought a 52mm 6point screw on Star filter for £2.49 as most of my effects filters are A square filter that I would have to use an adaptor with and I find it a bit of a hassle these days.

Any CC or hints and tips on using this filter would be appreciated.

It can be viewed bigger by clicking on the poicture and on photobucket click on the zoom tool at the bottom right hand side pof the pic.

 

 

Edited May 11, 2013 by NannyFerret

[Guest DaveW]

As I thought it works on crossed polarisation Nanny, being two polarising filters that darken as you twist one and their planes of polarisation cross. Evidently a linear polariser in front of a circular polariser. A circular polariser at the rear is needed by most modern cameras since they have a beam splitter or semi-silvered mirror in the meters light path and simply rotating a linear polariser in front of the camera alters the proportion of light to meter and focusing screen, hence can produce wrong exposure, plus also upset autofocus too.

 

See:-

 

http://www.benjaminmoritz.com/2011/03/1074

 

http://photo.tutsplus.com/articles/hardware/an-in-depth-comparison-of-two-variable-neutral-density-filters/

[NannyFerret]

I thought that's how it worked, but it doesn't actually make the sky blue or the clouds whiter as a circular polariser does and is the more grey/neutral colour that my other ND lens is; 

I have used circular and linear polariser filters and the Autofocus has always worked ok.

Not sure about this one as have only tried it very quickly and asit was hand held I couldn't keep it steady and a fast shutter speed would have made it too dark. 

I guess I need to do a lot more experimenting.

[Guest DaveW]

A polariser only darkens skies at 90 degrees to the sun and the vario is crossed polarisers anyway.  Whether meter or autofocus works OK with a linear polariser depends if the light path to meter, viewfinder and autofocus sensor is split between them by a semi silvered mirror or beam splitter. If it is the camera manufacturer adjusts the meter and autofocus to take account of what proportion in normal light goes to each. As I understand it when you use a linear polariser it's rotation alters these proportions so you get progressively more metering and autofocus inaccuracies as the polariser is rotated.

 

A circular polariser is simply a linear polariser with what is called a quarter wave plate on it's rear surface.  This changes the light having passed through the linear polariser to circular polarised light without affecting the linear polarisers effect, but the circular polarised light does not affect the light proportions to autofocus or metering.

 

http://en.wikipedia.org/wiki/Polarizing_filter_(photography)

 

A lot of photographers think if you put a polariser on a camera it will darken the sky wherever you point the camera.  But you only get the band of maximum polarisation at 90 degrees to the sun, meaning with the sun at right angles to the lens. You don't notice this much with normal lenses, but with wide angle ones you may get an unevenly darkened sky, which is why they don't recommend using polarisers for sky darkening with wide angle lenses, as in the picture in the link below..

 

http://photo.net/digital-darkroom-forum/00Cw15

 

http://www.cameratechnica.com/2011/04/10/the-science-of-polarizing-filters/