Peter Ellis will cover the topic of filters at the next Development Group meeting, on Monday 2 September at OBC.  He kindly provided the following background material:

FILTERS

The word “filter” covers a vast range of topics in photography.  Our September meeting will consider some of the more interesting and widely used filters.  It will start with an illustrated talk and demonstrations that will try to answer some of the questions regarding the types of filters and their uses.  The talk will be followed by a discussion session.

Filters come in all sorts of flavours, but fall into two general categories.  The first and oldest is the “real” category.  These are the filters that mostly originated in the days of film cameras that can be held in the hand and attached to your camera or enlarger.  Your digital camera will come with at least one real filter embedded inside it.  The other category is the digital filter that resides in your computer.  Hundreds of these exist in very many digital image processing packages.  This presentation will make use of the filters in Adobe Photoshop, but most of them are also available in other software products.

Some of the questions about “real” filters that will be addressed are:

  • Are filters developed for black and white film photography still useful in the digital age?
  • Why does a digital camera have an infra-red blocking filter inside it, and can this type of camera be used for taking infra-red pictures?
  • What is the difference between near infra-red and far infra-red photography?
  • How does a polarizing filter work and why do we need a circular polarizer for some types of camera?
  • What can a polarizing filter be used for?
  • What other types of “real” filter are there, and what can they be used for?

Questions about “digital” filters include:

  • What is the basic difference between a film camera image and a digital camera image?
  • What are the problems when using sharpening filters to retrieve the detail in blurred images?
  • How can digital filters be used in conjunction with layer blending modes such as those found in Photoshop?
  • Which of the lesser known and lesser used filters are really useful?
This picture of the Waikanae river was taken with a digital camera in which the red channel has been replaced with an infra-red channel by switching out the internal infra-red blocking filter.  All visible light has been stopped with an external filter over the lens. The infra-red channel is then combined with the red and green visible channels (converting red to green and green to blue) to give this “false colour” picture.

This picture of the Waikanae river was taken with a digital camera in which the red channel has been replaced with an infra-red channel by switching out the internal infra-red blocking filter. All visible light has been stopped with an external filter over the lens. The infra-red channel is then combined with the red and green visible channels (converting red to green and green to blue) to give this “false colour” picture.

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