Could someone explain the difference in using colored filters for black and white photos? What is the best practice using these filters for portraits, landscapes, macro? For different types of weather: sunny, foggy, morning, evening, and so on?
If you are using a digital camera, there is little need to use colored filters, as you can apply their effects in post processing when you do the black and white conversion.
If you are shooting film, then
- Red is commonly used in landscapes. It will darken foilage, and will dramatically increase the constrast in cloudy skies. It will lighten skin if used in portraiture.
- Orange behaves like red, but effects are less.
- Yellow has a subtle effect - will darken skin slightly.
- Green will lighten foilage. It can be used in portraits to darken the skin
- Blue will lighten skies, and lower contrast if you want a hazy effect
The easiest way to remember the effect of a filter is this: a filter lightens its own color and darkens the complementary color. A color wheel illustrates the concept. Colors that are 180° opposite are complements of each other.
From the color wheel, we can learn that a green filter will lighten some foliage (foliage does not read completely green, but green-yellow), and darken reds (some complexion contains red — be careful because this may make skin complexions a bit blotchy for people with ruddy complexions).
The red filter is the "landscape filter" because it tends to produce dramatic skies — the dark sky against white cloud or snowy peak effect that is so appealing in black & white images. It lends a slightly ghostly effect to green foliage, particularly evergreens.
I've attached some simulated B&W effects on an image that includes sky, foliage, and clouds. This is simulated using NIK Silver Efex, so it's not exactly like using glass, but it's darn close:
As others have said, different filter colours will affect the different colours and thus affect the different grays the picture shows.
A way to decide which filter to use is to half close your eyes and see which colours belnd in too much or which stand out too much.
Having compared the pics given by Steve Ross by downloading them a flipping between them in 'slideshow' mode of windows picute and fax viewer, I would suggest that the Red and Yellow filter pics have been mixed up.