What do filters do?

-- James Cooper (rc@sover.net), July 23, 1998

Answers

in respond to: What do filters do?

Many books have been about filters in B&W and Color photography  I will give you some brief intro, and if you interested to know more find a good book and enjoy.

B&W photograph is created by transition of color image into a range grays varying from black to white. Spectral sensitivity of B&W process (choice of film and development) defines the final result.

Using color filters makes possible to alter the color range of a scene (as exposed on the film) so it will be rendered differently in the final print. For example, RED filter will cause blue sky to appear darker, GREEN filter can be useful to make trees and plants look brighter. Additionally there are special effects filters, which allow to distort or alter an image to obtain figurative effects.

Very useful is the polarizer filter, which is used for two main purposes: eliminate reflections from shiny surfaces and darken sky in color photography (best effect when the sun is at your side).

Mechanically speaking there are two types of filters: front-mount screw-in and square insert-type filters. Screw-in filters are generally of a better quality (made from optical glass, flat, polished and multi-coated - to reduce reflection) but they are more expensive. The other type are square plastic filters of much lower optical quality, but available in an enormous variety of colors and effects. These filters require an adapter, which is mounted on the lens and allows insertion of two or three filters simultaneously (so effects can be combined).

By default, I personally always have a UV filter (almost neutral both for B&W and Color) mounted on all my lenses  mainly for protection of the front element from scratches. NOTE: never put two screw-in filters in tandem it will certainly cause vignetting (dark shadows in the corners of the image)  if required exchange filters.

Some recommendations: If you can afford it use brand name filters (Nikon, Canon, Minolta, Olympus,) or filters from HOYA (a well known German optical glass supplier). For flat filters  I think Cokin has the widest range and availability.

If you have lenses of different front screw diameter (e.g. my Minolta lenses are of 55mm or 49mm diameter) it is possible to use a step-up ring (e.g. 49->55mm) so you can use only a larger diameter filters  I am lazy so I have two sets of filters. For the bigger diameter (64 and 72mm) there is no choice but purchase individual filters.

Hope this gave you some starting point information.

Zeev Kantor

-- Ze'ev Kantor (zeevk@netvision.net.il), July 25, 1998.