ND fader filter?

juliettekw

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I saw some photographs in DSLR magazing of daytime long exposures and need to create similar images for art coursework. They used a circular neutral density fader filter which apparently you can pick up for around £20, I was just wondering what the difference between one of these and a polarizing filter is and could I just use a polariser instead? Thanks
 
I saw some photographs in DSLR magazing of daytime long exposures and need to create similar images for art coursework. They used a circular neutral density fader filter which apparently you can pick up for around £20, I was just wondering what the difference between one of these and a polarizing filter is and could I just use a polariser instead? Thanks

A polarizer generally won't reduce the ambient light enough to get the shutter speed where you need it. A Variable Neutral Density filter usually will. Polarizers only cut the light a couple stops.... VNDs can go to 10 stops.

And like anything else in this world, the cheap ones aren't worth the money.
 
A neutral density filter (also called a fader) will darken all or a portion of the image without any color shift. Neutral density filters have 3 types: fixed darkening amount, graduated (darker on top, less dark on the bottom, for example), or may be variable (a twist of the filter makes the entire image darker or lighter).

The fixed amount ND filters will darken the entire picture one or more stops (or portions of), causing the camera to require a longer exposure to capture the image. Multiple fixed ND filters may be combined to make it darker than a single filter. Making moving water 'smooth' or 'silky' is a prime example. Pre-1960 movies used fixed ND filters to shoot nighttime (appearing) scenes in daylight, as the films were too slow (low ASA/ISO) to be used at night. Graduated ND filters with a darker top are frequently used to photograph sunsets with subjects 'below' the sun that need more exposure. The best types of these filters are square or rectangular and may be moved up and down to move where the horizontal light/dark transistion occurs in the picture before the shutter is opened. Variable ND filters do the function of multiple fixed amount ND filters, with any amount of darkening desired, all in a single filter.

Polarizing filters, on the other hand, although they appear to be made from darker glass, they are not. Instead, it is blocking all the light perpendicular to the polarization. Its biggest use is to eliminate reflections from smooth surfaces like glass or water. They also have a tendency to darken the sky a bit making it more 'vibrant'. Circular polarizing filters are rotated on-camera (lens) to achieve the 'right' amount of polarization. Achieving the desired effect is dependent upon where the camera is, the reflection is, the angle of the camera sensor in relation to the reflecting surface, and, the rotated 'directional position' of the polarizing filter.

ND filters and polarizing filters are the most commonly needed filters in digital photography. UV and clear 'protection' filters are a complete waste of money and may cause unwanted image degradation, ghosting, filter-flare, bluriness, and even lens damage if broken.

Like most photographic equipment, quality does not come cheap. In general, filters costing less than about $100 (US) frequently lack the better coatings needed to prevent ghosting, flare, etc. The cheaper filters of any kind will usually cause the most image degradation because of the lack of quality materials/coatings/manufacturing. Some manufacturers such as Hoya produce multiple lines of the same filter types at various price levels, with better quality filters progressively more expensive. For example, at my favorite online photography equipment store, Hoya 72mm fixed amount ND filters vary in price from $32 to $100. Various manufacturers 72mm variable ND filters vary in price from $35 to $383. Square/rectangular ND filters from one manufacturer vary in price from $20 to $300...plus a one-time cost of filter holder and adapter, usable with all their filters. ALthough filters are less costly than lenses, one does not want to be forever buying better and better filters because of problems caused by lesser quality filters.
 
So if I understand your question right, you just want to take a long exposure in daytime?

You need to decrease the light coming onto the sensor... You could indeed use a polarizer to maybe double, or quadruple the exposure time. Add to that a really small apereture (say f 22 or f 32 if you can get it on your camera) and super low iso, and you might be able to get a longer exposure.

The question is, how long exposure do you need?

1 second would provide you blur if that's what you're going for and might be possible if it's not very bright out

But if you're looking for, say, a minute long exposure you'll need a ND filter. OR to shoot out when it's darker out (maybe twilight)
 
Neutral density filters are typically either sold as a number of "stops" OR as a "density" value. If it's represented as "density" value then what you need to know is that each ".1" density is equal to 1/3rd of a stop. That means an ND 0.3 is blocking 1 full stop of light (each 1 full stop blocked means that only half the light gets through. 2 full stops means you get half of the half... or 1/4 of the light gets through, etc.)

The variable ND filters are putting two polarizers together. As you twist them, they block more or less light.

The "graduated" ND filters usually are not round thread-on filters, but rather rectangular slides which go into a holder (e.g. usually a Cokin brand filter holder or a similar product. Just know that Cokin holders come in various widths so you have to buy the correct width based on the size of your filters AND it needs to be wide enough that the wides lens you use it with will not be able to see the edges of the filter holder in the field of view.

If you only buy 1 ND filter then a 3-stop filter (ND 0.9) is a pretty good starting filter. A polarizer can often block just about 2 stops (although that can depend on the angle of the light). That means you could stack an ND and a polarizer together for stronger blocking.

I always have a 3 stop ND (ND 0.9) a 2 stop ND (ND 0.6) and a circular polarizer in my bag.
 

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