diglloyd
diglloyd publication
Imagery: Auto - Large Table of Contents
Pentax 645D
Pentax 645D

Sensor Color Uniformity

Medium format digital sensors often have non-uniform color rendition across the frame, typically leading to a blue or cyan cast into the corners of the frame. While lenses can also be involved (wide angle lenses in particular), longer focal lengths typically do not contribute much to the issue.

I had two lenses to test: the 55mm f/2.8, and a manual focus 75mm f/2.8. I tested both, with very similar results.

Example with 75/2.8

It’s curious that while Pentax offers lens correction for both distortion and chromatic aberration, it is not offered for this color shift into the corners. Nor does Adobe Camera RAW correct for it using the Adobe-supplied lens correction for the 75/2.8.

The image below is of a gray sky, with a 50 pixel Gaussian Blur to remove minor variations in density, taken at f/5.6 with the 75mm f/2.8. White balance was neutralized at image center, where the image is completely neutral, as measured in Photoshop.

Article continues for subscribers...

If you’re already a subscriber, CLICK HERE TO LOG IN

diglloyd Advanced Photography

diglloyd Advanced Photography includes hundreds of pages of exclusive coverage and high resolution, Retina-grade example pictures detailing Canon and Nikon DSLR bodies and their lenses, with in-depth analysis of sharpness and contrast, color, bokeh, vignetting, distortion, MTF, and flare. Also included is a wealth of in-context technique and workflow insight. Since 2006, diglloyd Advanced Photography is the authoritative review and on-line reference for discerning Canon and Nikon shooters. Subscriptions cost $ per year.

  1. Explore the table of contents
  2. Check out Lloyd Chambers’ Blog
  3. Subscribe today!
img
Variants gray, pureGray available in full article
Pentax 645D + Pentax-A SMC 75mm f/2.8 @ f/5.6, 1/200 sec, ISO 100

diglloyd Home Page | Terms of Use | PRIVACY POLICY | Contact
Copyright © 2008-2015 diglloyd Inc, all rights reserved.