post5: type of filter
ND / GND and the FADER ND.

now, we all know, but setting small enough the aperture (large F/# number) by chance, u get very small light going into your sensor, to gain long shutter speed. but, what if, i wanted to shoot F1.4 are board daylight? or strobe a photo with 1/250ss sync limit?

we grab ND filters.

what are ND filters?
ND filter are a 'dark' piece of filter that cuts down light evenly. Neutral Density, like the name, will reduce light of all color, equally, without changing the saturation/hue of the color rendition. so, No, it will not end up with a more 'red'er color cast photo, unless, its a cheap made in china coated ND filter.

so, what are the uses?
its is subjective base on what you need it for? since there are so many 'level' of ND available for different application.

i) you can use it to do a long shutter on daytime, depending on application, say, a dream effect of waterfall.
[attachmentid=2249347]
(6stop) ND8+4+2 (cokin)filter was used with a GND4 to cut off the top part. that why the tree looks darker

ii) you wanted to get the shallow DOF out of F1.4 under the sun, but turn out overexposed, use ND to cut down the amount of light going into the sensor.

how do we scale ND filters? *chart taken from wikipedia
link removed.

How about GND? *coming really soon.
GND is a little diff by its application and look. the ND is apply gradient-ly over the filter. top to bottom. what it uses is to reduce light on one side of the frame. usually used to reduce the strong bright sky.