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photo:lensperspective

perspective control, shift and/or tilt lenses

introduction:

  • whilst perspective control using shift lenses to correct converging lines can be largely done in post-processing in tools such as Photoshop, the ability to change the plane of focus by using a tilt lens cannot be achieved satisfactorily in PS.
  • a tilt lens can be very useful for product photography as well as macrophotography or even portraiture but accurate focus of the distorted focal plane ideally requires use of Live Preview such as in the Canon 1D MarkIII.
  • some medium format film camera systems (eg. Fuji GX680III, Linhof 679 view, Horseman VR)and practically all large format cameras have tilt and shift capability via use of bellows.
  • changing the plane of focus using tilt lenses:
    • the amount and direction of the tilt determines where the Hinge line is.
    • any movement of the camera back towards or away from the lens (eg. by changing focus ring) causes the plane of sharp focus to rotate about the Hinge Line.
    • the plane of focus is formed by a line passing through 2 points:
      • a fixed point (Hinge line) for a given degree of rotation & tilt of the lens located directly below the lens at the intersection of 2 lines:
        • a line parallel to the film plane at the level of the lens
        • a line parallel to the lens tilt which lies 1 focal length in front of the lens
        • to determine which tilt angle to use based on the vertical distance (J in feet) from the lens which this point is placed can be determined by the equation:
          • tilt angle = arcsin(focal length/J)
          • if focal length in mm and J in feet this approximates to tilt angle = f/5J.
          • eg. if using TSE90mm lens with 8mm tilt, this point is ~2.25 feet from lens (4.5 feet if 4mm tilt)
      • a moving point (Scheimpflug line) along the lens plane which intersects with a line parallel to and intersecting with the film plane
  • perspective control using a shift lens:
    • to determine how far from a subject you need to be to avoid convergence, use the following equation:
      • subject distance = actual focal length in mm / (height above centre of film in mm x target height)
      • on a full frame sensor with 11mm shift:
        • landscape: height above centre of film = 23mm
        • portrait: height above centre of film = 29mm
          • thus with 90mm lens, subject distance must be more than 3.1x the subject height
      • on a APS-H sensor (eg. Canon 1D series) with 11mm shift:
        • landscape: height above centre of film = 20mm
        • portrait: height above centre of film = 25mm 
          • thus with 90mm lens, subject distance must be more than 3.6x the subject height
      • a teleconverter multiplies both the focal length and the amount of shift.
      • hope I got all this right.
      • NB. at the extremes of shift, vignetting effect will occur as angle of light to film plane becomes more acute.
  • perspective control in Photoshop:
    • via Filter:
      • Filters:Lens Distortion then adjust vertical & horizontal perspective distortion
    • via Transform:
      • Select:All then Edit:Transform:Perspective then adjust the handles to correct the distortion
    • in either case, this will result in a converging edge to your image which will then require cropping to get back to a rectangular format, thus there is a cost in potentially detail but also in loss of pixels due to cropping.
  • pseudo-tilt effect in PS:
  • perspective control using the LensBaby tilt/shift lens:
    • these new lenses are fairly cheap and can be fitted to most dSLRs to primarily provide creative images rather than technically perfect commercial images as with most other perspective control lenses.
    • these lenses are NOT trye perspective control lenses but just provide a central sharp area with surrounding blur, and the location of this central sharp area can be moved around the frame although it becomes less sharp the further it is moved from the centre - and at its best, its not that sharp.
    • unfortunately to change aperture you must physically replace the aperture stop
    • in most cameras, aperture-priority metering works but in some Nikons you must use manual metering.
    • $US270 for current 3G version & only weighs 162g.
      • 50mm focal length;
      • minimum focus 30cm;  
      • aperture stops f/2 through to f/22.
    • see http://www.dimagemaker.com/article.php?articleID=979 and http://www.dimagemaker.com/lensbaby-photography/lensbaby.php - tests to demonstrate use at different apertures and for infrared use.
    • but you can achieve similar results in Photoshop using radial blur, etc, this lens saves you time on the computer but at a cost of less versatility in changing the end result.
    • www.ayton.id.au_gary_images_lensbaby3g.jpg

Micro Four Thirds:

  • fortunately with MFT cameras you can buy tilt or shift adapters which allow you to convert almost any lens designed for 35mm to a tilt or shift lens and you get HD video - and if using an Olympus body, it will be image stabilised - just awesome!!
  • you can use Canon EF tilt shift lenses via EF adapter but you must change aperture with lens on a Canon body
  • you can use Nikon PC or Olympus OM shift lenses via adapter as with Four Thirds cameras

Canon dSLR options:

Nikon dSLR options:

Olympus dSLR options:

  • can use any as listed under Canon except Cambo/Horseman solutions or Canon EF lenses but 2x crop may be an issue.
  • be aware though that the flash housing on some Olympus dSLRs may get in the way of the knobs on some of these lenses.

 

photo/lensperspective.txt · Last modified: 2013/06/28 17:27 by gary1