Forgot Password
Pentax Camera Forums Home

Show Printable Version Search this Thread
05-23-2009, 06:44 PM   #1
Veteran Member
mattdm's Avatar

Join Date: Feb 2007
Location: Boston, MA
Photos: Gallery
Posts: 2,964
1.53 vs. 1.54 (or even 1.57) and actual image size

So, not that I actually care about the tiny fraction of a difference we're talking about here, but I just noticed that in this wikipedia entry

APS-C - Wikipedia, the free encyclopedia

the K20D is listed as having a crop factor of 1.54 rather than the 1.53 listed for all of the other Pentax dSLRs.

Sure enough, the specs give the K20D as having a
23.415.6mm sensor rather than the older 23.515.7. So, that gives 1.5385 instead of 1.5319 horizontally.

But then, there's the issue of _effective_ pixels every dSLR uses some of the edge of the sensor for determining black level, demosaicing the edges, etc. So, I wonder if despite the fractionally smaller sensor chip itself the actual imaging area is identical. I notice that the K10D uses 10.2m of 10.75m actual pixels (5.39% excess) whereas the K20D uses 14.5m of 15.1m (4.14% in excess). Since the fraction is somewhat lower, I speculate that the actual image area is virtually identical.

In fact, assuming that the above percentage of pixels is removed from each, that gives the actual image size for both as about 22.915.3 or a "real" crop factor of 1.57.

(I put "real" in quotes because typical prints crop the edge of 35mm full-frame anyway, and because surely the same issue affects full-frame dSLRs, which also have approximately 5% more photosites than effective pixels.)

It's all really pedantic and doesn't seem even slightly important. Still, I'm curious. Anyone know the answer?


  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Tags - Make this thread easier to find by adding keywords to it!
camera, crop, dslr, edge, factor, full-frame, identical, image, issue, k20d, photography, pixels, sensor
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Similar Threads
Thread Thread Starter Forum Replies Last Post
Image Size tcwilson Troubleshooting and Beginner Help 6 11-10-2010 07:29 PM
Image Size vs Document Size vs Resolution vs Resampling vs ... AHHHH! veezchick Digital Processing, Software, and Printing 13 08-02-2010 03:57 PM
Image size Jacos Troubleshooting and Beginner Help 15 04-11-2010 02:47 PM
JPEG Image Size hcc Troubleshooting and Beginner Help 21 04-10-2010 08:44 PM
Actual RAW file size and recordable image number Matjazz Pentax DSLR Discussion 12 04-01-2009 04:33 PM

All times are GMT -7. The time now is 09:14 AM. | See also:, part of our network of photo forums!
  • Red (Default)
  • Green
  • Gray
  • Dark
  • Dark Yellow
  • Dark Blue
  • Old Red
  • Old Green
  • Old Gray
  • Dial-Up Style
Hello! It's great to see you back on the forum! Have you considered joining the community?
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]