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the last word

Photography meets digital computer technology. Photography wins -- most of the time.

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NEX-7 — correcting images with purple corners

January 6, 2012 JimK Leave a Comment

I have been using Cornerfix to correct NEX-7 images that have discolored edges and corners. It does the job, and it does it well. It supports batch processing, which is useful. Originally written to correct deficiencies in Leica M8 images, it works with any camera for which a Adobe DNG file can be generated. Here’s… [Read More]

The Last Word

NEX-7 — purple corner testing summary

January 5, 2012 JimK 5 Comments

Ignoring the brightness falloff towards the corners, which is easy to deal with in image editing and may prove to be esthetically appealing, the most important measure of the purple-corner effect is the change in chrominance (that portion of color that is unrelated to luminance). CIELab provides a formula for calculating chrominance:  (a^2 + b^2)^.5…. [Read More]

The Last Word

NEX-7 — Lens testing for purple corners

January 5, 2012 JimK Leave a Comment

I’ve now completed making the test images for the following lenses, using the methodology of the previous post: Sony 16mm f/2.8 E mount Leica Tri-Elmar 16/18/21mm f/4 Leica Super-Elmar 18mm f/3.8 ASPH Leica Elmar 24mm f/3.8 ASPH Leica Elmarit 24mm f/2.8 ASPH Zeiss Biogon 35mm f/2 Leica Summilux ASPH 50mm f/1.4 In this post, I’ll report the… [Read More]

The Last Word

NEX-7 — test images for corner color correction

January 4, 2012 JimK Leave a Comment

Cameras like the NEX-7, with their high resolution sensors and low flange distances, return to photography the kind of flexibility in lens selection associated with view cameras. That flexibility is not without cost. There is a loss in automation, which is no big deal to most of us. The biggest effect is that the responsibility… [Read More]

The Last Word

NEX-7– purple corners

January 2, 2012 JimK 3 Comments

Near the start of my NEX-7 postings, a reader asked me if I saw purple corners when the camera is used with wide angle lenses. I replied that I had noticed the effect with the 24 mm Elmar. I’ve had a chance to do some more reading and some more experimentation, and here’s what I’ve… [Read More]

The Last Word

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Articles

  • About
    • Patents and papers about color
    • Who am I?
  • How to…
    • Backing up photographic images
    • How to change email providers
    • How to shoot slanted edge images for me
  • Lens screening testing
    • Equipment and Software
    • Examples
      • Bad and OK 200-600 at 600
      • Excellent 180-400 zoom
      • Fair 14-30mm zoom
      • Good 100-200 mm MF zoom
      • Good 100-400 zoom
      • Good 100mm lens on P1 P45+
      • Good 120mm MF lens
      • Good 18mm FF lens
      • Good 24-105 mm FF lens
      • Good 24-70 FF zoom
      • Good 35 mm FF lens
      • Good 35-70 MF lens
      • Good 60 mm lens on IQ3-100
      • Good 63 mm MF lens
      • Good 65 mm FF lens
      • Good 85 mm FF lens
      • Good and bad 25mm FF lenses
      • Good zoom at 24 mm
      • Marginal 18mm lens
      • Marginal 35mm FF lens
      • Mildly problematic 55 mm FF lens
      • OK 16-35mm zoom
      • OK 60mm lens on P1 P45+
      • OK Sony 600mm f/4
      • Pretty good 16-35 FF zoom
      • Pretty good 90mm FF lens
      • Problematic 400 mm FF lens
      • Tilted 20 mm f/1.8 FF lens
      • Tilted 30 mm MF lens
      • Tilted 50 mm FF lens
      • Two 15mm FF lenses
    • Found a problem – now what?
    • Goals for this test
    • Minimum target distances
      • MFT
      • APS-C
      • Full frame
      • Small medium format
    • Printable Siemens Star targets
    • Target size on sensor
      • MFT
      • APS-C
      • Full frame
      • Small medium format
    • Test instructions — postproduction
    • Test instructions — reading the images
    • Test instructions – capture
    • Theory of the test
    • What’s wrong with conventional lens screening?
  • Previsualization heresy
  • Privacy Policy
  • Recommended photographic web sites
  • Using in-camera histograms for ETTR
    • Acknowledgments
    • Why ETTR?
    • Normal in-camera histograms
    • Image processing for in-camera histograms
    • Making the in-camera histogram closely represent the raw histogram
    • Shortcuts to UniWB
    • Preparing for monitor-based UniWB
    • A one-step UniWB procedure
    • The math behind the one-step method
    • Iteration using Newton’s Method

Category List

Recent Comments

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  • JimK on Fuji 20-35/4 landscape field curvature at 23mm vs 23/4 GF
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