ND filters ???
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- Tim
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I can't point you to a website, but here's my take on it....
There are two main types - plain ND filters and graduated ND filters. The former allows you to use longer shutter speeds, without stopping down too much and suffering from diffraction softening. Such uses would be for smoothing waterfalls and streams or using slow shutter speeds when panning motorsport and wanting to use a wide aperture to keep any fencing out of focus. Also, if using fill flash for portraiture on a bright day an ND filter can allow you to maintain a wide aperture for subject isolation, while still firing the flash at the sync speed, thus extracting maximum reach from the flash.
If you consider the lighting conditions you might be shooting in, and your desired aperture and shutter speed, you can figure out how many stops you need the filter to lose. e.g. on a bright, sunny day, shooting at 100 ISO and f/11, you would ordinarily need a shutter speed of around 1/200 for a correct exposure. If you wanted to shoot with a shutter speed of 1/2 second, for example, you need to lose a lot of light with the filter. So, here's how the shutter speed varies as you increase the density of your filter...
0 stops : 1/200;
1 stop : 1/100;
2 stops : 1/50;
3 stops : 1/25;
4 stops : 1/13;
5 stops : 1/6;
6 stops : 1/3;
7 stops : 0.6 (close to what you want);
8 stops : 1.2.
You'll probably find a use for filters anywhere between 1 stop and 10 stops, and usually having a set of filters allows you to fine tune the effect you seek, and to deal with differing levels of incident/ambient light. You could use a CPL as a ~1.5 stop ND filter, at a pinch, and there are variable ND filters available, constructed from a pair of polarisers joined to gether. As you twist them relative to each other they will allow more or less light through, giving you a wide range of infinitely variable options. As with most things, you get what you pay for.
There are also soft and hard graduated ND filters, which have part of the filter darkened and part of it clear. There might be a hard/rapid change at the boundary between clear and dark, or a soft/gradual change. Either way, the idea behind such filters is to reduce the brightness of some part of the scene - typically the sky - so that you can get a proper exposure of the foreground without blowing out the sky. Hard grads are used when there is a clear division between sky and foreground, such as the horizon of a seascape, whereas soft grads are used when you have an uneven division between sky and land, such as a cityscape, with bits and pieces of "foreground" jutting up into the sky.
Ideally, grads will be rectangular, and fit into a filter holder so that they can be slid up and down to position the darker part exactly where you need it. Cheaper options, of square or screw on filters will restrict your compositional flexibility.
You might find that a combination of both plain ND and graduated ND is needed if you want to achieve a long exposure for a scene that also has high contrast, with a bright sky and dark foreground. There is a thread over on POTN at the moment showing ND grads in use....
http://photography-on-the.net/forum/showthread.php?t=224448
The daddy of filter systems if, as far as I know, the Lee Filters, but they are expensive. For less money there is Hitech, also good (so I hear) or cheaper still (though still expensive) Cokin. I've just bought a Cokin Z-Pro ND grad set, which together with 77mm and 82mm lens adapter rings cost me about £170 in all. To buy the Lee equivalent would have cost something like £250 or so, maybe more.
There are two main types - plain ND filters and graduated ND filters. The former allows you to use longer shutter speeds, without stopping down too much and suffering from diffraction softening. Such uses would be for smoothing waterfalls and streams or using slow shutter speeds when panning motorsport and wanting to use a wide aperture to keep any fencing out of focus. Also, if using fill flash for portraiture on a bright day an ND filter can allow you to maintain a wide aperture for subject isolation, while still firing the flash at the sync speed, thus extracting maximum reach from the flash.
If you consider the lighting conditions you might be shooting in, and your desired aperture and shutter speed, you can figure out how many stops you need the filter to lose. e.g. on a bright, sunny day, shooting at 100 ISO and f/11, you would ordinarily need a shutter speed of around 1/200 for a correct exposure. If you wanted to shoot with a shutter speed of 1/2 second, for example, you need to lose a lot of light with the filter. So, here's how the shutter speed varies as you increase the density of your filter...
0 stops : 1/200;
1 stop : 1/100;
2 stops : 1/50;
3 stops : 1/25;
4 stops : 1/13;
5 stops : 1/6;
6 stops : 1/3;
7 stops : 0.6 (close to what you want);
8 stops : 1.2.
You'll probably find a use for filters anywhere between 1 stop and 10 stops, and usually having a set of filters allows you to fine tune the effect you seek, and to deal with differing levels of incident/ambient light. You could use a CPL as a ~1.5 stop ND filter, at a pinch, and there are variable ND filters available, constructed from a pair of polarisers joined to gether. As you twist them relative to each other they will allow more or less light through, giving you a wide range of infinitely variable options. As with most things, you get what you pay for.
There are also soft and hard graduated ND filters, which have part of the filter darkened and part of it clear. There might be a hard/rapid change at the boundary between clear and dark, or a soft/gradual change. Either way, the idea behind such filters is to reduce the brightness of some part of the scene - typically the sky - so that you can get a proper exposure of the foreground without blowing out the sky. Hard grads are used when there is a clear division between sky and foreground, such as the horizon of a seascape, whereas soft grads are used when you have an uneven division between sky and land, such as a cityscape, with bits and pieces of "foreground" jutting up into the sky.
Ideally, grads will be rectangular, and fit into a filter holder so that they can be slid up and down to position the darker part exactly where you need it. Cheaper options, of square or screw on filters will restrict your compositional flexibility.
You might find that a combination of both plain ND and graduated ND is needed if you want to achieve a long exposure for a scene that also has high contrast, with a bright sky and dark foreground. There is a thread over on POTN at the moment showing ND grads in use....
http://photography-on-the.net/forum/showthread.php?t=224448
The daddy of filter systems if, as far as I know, the Lee Filters, but they are expensive. For less money there is Hitech, also good (so I hear) or cheaper still (though still expensive) Cokin. I've just bought a Cokin Z-Pro ND grad set, which together with 77mm and 82mm lens adapter rings cost me about £170 in all. To buy the Lee equivalent would have cost something like £250 or so, maybe more.
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- Scott
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The 'orthodox way' is to get your "base exposure", that is, get a reading for the foreground in Manual mode using centre weighted metering, you will us this reading as your exposure time.
Then take a reading for the sky. If the sky is 3 stops brighter than the foreground, use the 0.9, if it is 2 stops brighter use the 0.6. and so on.
The more advanced way will be to use spot metering on foreground midtones but is a little trickier and for the more experienced.
I would recommend you buy the Lee Inspiring Professionals book. A great source of info to get you started.
http://www.leefilters.com/camera/products/range/ref:I46CC007258785/
Rgds
Then take a reading for the sky. If the sky is 3 stops brighter than the foreground, use the 0.9, if it is 2 stops brighter use the 0.6. and so on.
The more advanced way will be to use spot metering on foreground midtones but is a little trickier and for the more experienced.
I would recommend you buy the Lee Inspiring Professionals book. A great source of info to get you started.
http://www.leefilters.com/camera/products/range/ref:I46CC007258785/
Rgds
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they are merely a light control filter which gives the apparent cutting down in iso dependent on the factor involved....which are literally stops
good for slow speeds in daylight combined with small apertures to do the world famous foggy water and misty tides
good for slow speeds in daylight combined with small apertures to do the world famous foggy water and misty tides
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- Name
- Mark
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The 'orthodox way' is to get your "base exposure", that is, get a reading for the foreground in Manual mode using centre weighted metering, you will us this reading as your exposure time.
Then take a reading for the sky. If the sky is 3 stops brighter than the foreground, use the 0.9, if it is 2 stops brighter use the 0.6. and so on.
The more advanced way will be to use spot metering on foreground midtones but is a little trickier and for the more experienced.
I would recommend you buy the Lee Inspiring Professionals book. A great source of info to get you started.
http://www.leefilters.com/camera/products/range/ref:I46CC007258785/
Which is where a decent spot lightmeter comes in very handy indeed
Rgds
