Stuck Filter Removal

Filter rings are generally made from either aluminum or brass. Lens barrels, particularly the threads to which filters attach, are usually made from aluminum.

Filter rings, particularly aluminum ones, can sometimes "bind" to the aluminum lens threads and be difficult to remove.

Aluminum is a relatively soft metal; attempting to remove a stuck filter by squeezing with the hand generally puts a lot of inward pressure on just the two areas being gripped; this can bend and deform both the filter ring and the lens threads, permanently weakening or damaging both and making the filter even more difficult to remove.

Methods should be employed that apply pressure evenly around the filter ring.

Typically this is achieved either by use of a filter wrench or by cupping the filter ring and front of the lens with a piece of fabric to protect them and provide friction, then pressing the combination against a hard surface and twisting the lens barrel.

Other aids to stuck filter removal include using either a tightened rubber band or shoelace around the rim of the filter to improve grip.

Filter Sizes & Mountings - Bayonet Round Filters

Certain manufacturers, most notably Rollei and Hasselblad, have created their own systems of bayonet mount for filters. Each design comes in several sizes, such as Bay I through Bay VIII for Rollei, and Bay 50 through Bay 104 for Hasselblad.

Filter Sizes & Mountings - Rectangular Filters

Graduated filters of a given width (100 mm, 67 mm, 84 mm, etc.) are often made rectangular, rather than square, in order to allow the position of the gradation to be moved up or down in the picture. This allows, for example, the red part of a sunset filter to be placed at the horizon. These are used with the "system" holders described.

Filter Sizes & Mountings - Square Filters

For square filters, 2" x 2", 3" x 3" and 4" x 4" were historically very common and are still made by some manufacturers. 100 mm x 100 mm is very close to 4"x4", allowing use of many of the same holders, and is one of the more popular sizes currently (2006) in use; it is virtually a standard in the motion picture industry. 75 mm x 75 mm is very close to 3" x 3" and while less common today, was much in vogue in the 1990s.

A French manufacturer called Cokin makes a wide range of filters and holders in three sizes which is collectively known as the Cokin System. "A" (amateur) size is 67 mm wide, "P" (professional) size is 84 mm wide, and "X Pro" is 130 mm wide. Many other manufacturers make filters to fit Cokin holders. Cokin also makes a filter holder for 100 mm filters, which they call the "Z" size. Most of Cokin's filters are made of optical resins such as CR-39. A few round filter elements may be attached to the square/rectangular filter holders, usually polarizers and gradient filters which both need to be rotated and are more expensive to manufacture.

Cokin formerly (1980s through mid-1990s) had competition from Hoya's Hoyarex system (75 mm x 75 mm filters mostly made from resin) and also a range made by Ambico, but both have withdrawn from the market. A small "system" range is still made (as of 2005) by Hitech. In general, square (and sometimes rectangular) filters from one system could be used in another system's holders if the size was correct, but each made a different system of filter holder which could not be used together. Lee, Tiffen and Singh Ray also make square / rectangular filters in the 100 x 100 and Cokin "P" sizes.

Gel filters are very common in square form, rarely being used in circular form. These are thin flexible sheets of plastic which must be held in rigid frames to prevent them from sagging. Gels are made not only for use as photo filters, but also in a wide range of colors for use in lighting applications, particularly for theatrical lighting. Gel holders are available from all of the square "system" makers, but are additionally provided by many camera manufacturers, by manufacturers of gel filters, and by makers of expensive professional camera accessories (particularly those manufacturers which target the movie and television camera markets.

Square filter systems often have lens shades available to attach to the filter holders.

Filter Sizes & Mountings - Threaded Round Filters

The most common standard filter sizes for circular filters include 30.5 mm, 37 mm, 40.5 mm, 43 mm, 46 mm, 49 mm, 52 mm, 55 mm, 58 mm, 62 mm, 67 mm, 72 mm, 77 mm, 82 mm, 86 mm, 95 mm, 112 mm and 127 mm.

Other filter sizes within this range may be hard to find since the filter size may be non-standard or may be rarely used on camera lenses.

The specified diameter of the filter in millimeters indicates the diameter of the male threads on the filter housing. The thread pitch is 0.5 mm, 0.75 mm or 1.0 mm, depending on the ring size.

A few sizes (e.g. 30.5 mm) come in more than one pitch.

Filter diameter for a particular lens is commonly identified on the lens face by the ligature "ø". For example, a lens marking may indicate "ø 55mm."

Photo Filter - Materials & Construction

Photo filters are commonly made from glass, resin plastics similar to those used for eyeglasses (such as CR39), polyester and polycarbonate; sometimes acetate is used. Historically, filters were often made from gelatin, and color gels, also called gelatin or simply gel filters are still used, but these are no longer actually made from gelatin, generally being instead made from one of the plastics mentioned above.

Sometimes a color is blended throughout the filter material, in other cases the filter is a sandwich composed of a thin sheet of material surrounded and supported by two pieces of clear glass or plastic.

Certain kinds of filters use other materials inside a glass sandwich; for example, polarizers often use various special films, netting filters have nylon netting, and so forth.

The rings on screw-on filters are most often made of aluminum, though in more expensive filters brass is used. Aluminum filter rings are much lighter in weight, but can "bind" to the aluminum lens threads they are screwed in to, requiring the use of a filter wrench to get the filter off of the lens. Aluminum also dents or deforms more easily. (See "Stuck filter removal" below.)

High quality filters have multiple layers of optical coating to reduce reflections and to allow more light to pass through the filter. Uncoated filters can block up to 9% of the light, while multi coated filters can allow for up to 99.7% of the light to pass through. Manufacturers brand their high-end multi coated filters with different labels, for example:

• Hoya: HMC (Hoya Multi Coating)
• B+W: MRC (Multi Resistant Coating)

Reflections can lead to flare and reduced contrast. Multi-layer coatings, which reduce this effect, are highly desirable in any filter. Exceptions to this rule are infrared and ultraviolet photography, where uncoated filters are usually used; multi-coated filters have a tendency to reflect more wavelengths outside the visible spectrum, making them unsuitable for such purposes.

Diopters & Split Diopters

Some argument could be made as to whether these are technically filters at all, or actual accessory lenses, however they are sold by filter manufacturers as part of their product lines, using the same holders and attachment systems.

Diopters are simple single or two-element lenses used to assist in close-up and macro photography.

They provide some number of positive optical diopters, which magnify the subject and allow objects very close to the lens to be brought into focus.

They are sometimes sold singly, and sometimes sold in kits of +1, +2, and +4 diopters, which allows them to be combined to produce a range from +1 to +7.

A split diopter is a diopter in which only half of the camera's lens area is covered by the filter.

A round split diopter has a usual filter ring, but is filled with only a semicircle of glass (or plastic).

This allows the photographer to photograph an object which is very close against a background much further away, effectively extending depth of field.

Careful composition is required to make effective use of this device.