Film photography is anticipated to endure for some time, as dedicated amateurs and skilled artists often prefer the use of traditional and familiar materials and techniques. The comparison of resolution between film and digital photography is complex. While the resolution of commercial 35 mm color film is estimated to be 19 megapixel, this measure may be misleading.

When considered in the context of film and lens in a camera, typical film achieves a resolution of about 40 line pairs per mm, or 80 dots per mm. This is equivalent of about 5.5 megapixels in the image of 35 mm film. In contrast to that, advertised pixel counts on digital cameras do not account for the actual number of pixels used to store the image, nor the effect of the Bayer pattern of sensor filters on the digital sensor, nor the image processing algorithm used to interpolate sensor pixels to image pixels. In addition, digital sensors are generally arranged in a rectangular pattern, making images susceptible to moire pattern artifacts, whereas film is immune to such effects due to the random orientation of grains.

The resolution of modern black and white slow speed film, exposed through a high quality prime lens working at its optimum aperture yields usable detail at a scanned file size of greater than 30 megapixels, with consumer 35mm color negative film an effective resolution of over 12 megapixels is achievable and in an inexpensive 35mm point and shoot camera a resolution of over 8 megapixels may be achieved. Film also offers ease of processing with drop off services for processing available in many locations, in contrast to digital photography where the process of printing can require the time and effort of the user in areas where commercial digital to print services are not yet readily available. A market of online printing of digital images has developed in response to this demand.

One major advantage of Digital photography is the ability to manipulate images given access to a personal computer. Software bundled with nearly all digital cameras today allows the user to modify the characteristics of the recorded image to produce a more desirable final image. More sophisticated users may choose to manipulate or alter the actual content of the recorded image. Another important advantage is the ability to evaluate a shot in real time, to decide if you wish to take another shot of the subject, in a different manner or with different settings. Images that are not appealing may be erased, freeing up storage space.

Nonetheless film still has advantages over digital, at least with current technology. One of the main advantages is its latitude, that is, the ability to produce a good image from over or under exposed negatives. Digital images which are slightly overexposed can lose all data in the highlights, and underexposed digital will lose significant shadow detail. Film, on the other hand, can be greatly over or underexposed and still be able to produce a normal image. This is particularly true with black and white film.

One useful approach to deciding between a film or digital camera is to consider the ultimate medium of display for your photographs. If your pictures are for display on computer or television screens, small format prints such as snapshot or 8x10" photo paper, then the resolution provided by a 5 to 9 megapixal digital camera may be adequate. If your final medium is magazine or poster images, or slides for projection, then you may need the resolution provided by film in order to get a satisfying product. Lower resolution images will look soft and/or noisy when printed or projected in large format.

The Oxford Companion to the Photograph, ed. by Robin Lenman

A filter is a camera accessory consisting of an optical filter that can be inserted in the optical path. The filter can be a square optical glass mounted on a holder accessory; or, more commonly, a glass or plastic disk with a metal or plastic ring frame, which can be screwed in front of the lens.
Filters are commonly used in black and white photography to manipulate contrast. For example a yellow filter will enhance the contrast between clouds and sky by darkening the latter. Orange and red filters will have a stronger effect.


Effects of using a polarizer and a red filter in black-and-white photography

Filters are less common in color photography and even less in digital photography. A major use is to compensate the effects of lighting not balanced for the film stock's rated color temperature (usually 3200K for professional tungsten lights and 5500K for daylight): e.g., the 80A blue filter used with daylight film corrects the orange/reddish cast of household tungsten lighting, while the 85 used with tungsten film will correct the bluish cast of daylight. Color correction filters are identified by numbers which sometimes vary from manufacturer to manufacturer.



Although the 80A filter is mainly used to correct for the excessive redness of tungsten lighting, it can also be used to oversaturate scenes that already have blue. The photo on the left was shot with a polarizer, while the one on the right was shot with a polarizer and an 80A filter:



Often in color photography, a polarizing filter will be used to darken overly light skys. The filter also whitens clouds and increases the contrast between the clouds and the sky. Atmospheric haze is also reduced and overall color saturation is increased.

The minuses:
The negative aspects of using filters, though often negligible, include the possibility of loss of image definition if using dirty or scratched filters, and loss of some exposure. The former is best avoided by careful use and maintenance of filters, while the latter usually will not be a problem if planned out properly.
Filters can be used also for special effects. A diffusion filter softens subjects and generates a dreamy haze; it can be improvised by smearing Vaseline on a UV filter.

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An infrared filter is a filter to remove visible light and only pass infrared light in different wavelengths. These are mainly used in infrared photography.
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A neutral density filter or ND filter is a "grey" filter. An ideal neutral density filter reduces light of all wavelengths or colors equally. The purpose of standard photographic neutral density filters is to allow the photographer greater flexibility to change the aperture or exposure time, allowing for more control, particularly in extreme circumstances.
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UV filters are used for general photography to reduce haziness or fogginess created by UV light. UV filters are transparent thus one doesn't have to remove it from his/her camera, moreover this is also why people use it as a protector filter for their lens. The UV filter absorbs ultra-violet and blue rays effectively without the increase of exposure.
Source: Wikipedia