Lens filter, whats the point of them?

Discussion in 'Projectors, Screens & Video Processors' started by DannyBoy73, Feb 2, 2009.

  1. DannyBoy73

    DannyBoy73
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    I've been reading threads owners threads and there's often reference to lens filters and the different settings to go with them.

    Whats the point of a lens filter and how does it improve the viewing?
     
  2. Peter Parker

    Peter Parker
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    A lens filter may be something as simple as a Neutral Density filter which just dims the image and can be used to reduce the screen reflectance to a particular level. Some pjs can be quite bright (especially on a small screen) so if you want an image brightness similar to what you'd find in your local commercial cinema, adding an ND2 or ND4 will do that for you. Later as the lamp dims with age (or if you want to watch some sports with the lights on and a few mates round) you can take the filter off.

    Other filters are used to optically correct the colour, usually because UHP lamps have less red light than green and blue, so when you get the pj it will have been set for a better colour balance to give video images a more accurate look they reduce the green and blue using the pjs digital controls). This usually reduces lumen output and contrast (because the black level doesn't change but reducing contrast reduces the white level and lumen output). Adding a red filter or an FL-Day filter for example will often optically colour correct the lamps red deficiency and allow more use of the green and blue, so you get more lumens and more contrast. The filter does reduce the overall lumen output but not as much as it would have done before recalibration. Overall effect in this case is a slightly dimmer image but more on/off contrast and better black levels.

    To correctly calibrate the RGB levels for an accurate greyscale with or without a filter you will need special tools and software, so it's not something that can be done by simply adding a filter.

    Gary
     
  3. DannyBoy73

    DannyBoy73
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    Awesome, cheers Gary, top explaination :thumbsup:
     
  4. Chopsus

    Chopsus
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    Ditto! I've been looking into getting an Xrite Eye One Display 2 and had not even thought about using filters to compensate if I get really bad results .... another tool in the box!

    Chops
     

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