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Tuesday, November 18, 2008

Focusing speed comparison Pentax K200D vs. K20D

I just got a new Pentax K20D, and it's a sweet upgrade to my K200D. One of the things I noticed right away is that it seemed to focus more quickly than my K200D. In order to quantify the difference I decided to take a page from the DPR technique for showing how quickly cameras fire in continuous shooting mode so I recorded the focusing sound and compared the waveforms visually to see how long focusing took.

This was a fairly quick and dirty test but I tried to keep it as accurate as I could given my limited attention span ;-) The setup. Using the Tamron 70-200/2.8 lens, I manually brought the lens out of focus to the close focus stop. Using my macbook I recorded the sound of the camera focusing on a subject about 12 or 13 feet away (unscientific). I first tested my K200D which shows full bars on the battery indicator (edit: NiMH rechargables), and which I think I remember changing recently (unscientific). I then tested the K20D which was showing 1/2 bar on the battery indicator, it was noticable faster than the K200D, but I had recently read a post on DPR stating that you'll get faster focus with a fresh battery, so I wanted to test that as well, so I swapped a charged batt. into the K20D and recorded that also.

Of note: Both cameras seemed to click when starting their focusing cycle, and I've determined through very quick and unscientific testing just now that if this lens is near it's focus stop, the camera starts it's focusing cycle by moving the focus to the stop before turning it the other way to achieve focus. I would theorize that this behavior is to rule out the focus point being in the small amount of travel between the current focus position and the stop. In each case, since the lens was basically at the stop already, I've started the time at the "click" of the lens hitting the stop, and stoped the time when there was no more discernible motor whine.

The findings...
  • K200D - 1.15 seconds
  • K20D with half power showing on the battery gauge - 1.00 seconds
  • K20D with a fresh battery - 0.84 seconds
So, the K20 is faster than the K200 and battery charge really does matter. If you're looking at these times and thinking, "The K20D takes one whole second to focus out to 12 feet? That's slow..." keep in mind that the Tamron lens used is a "macro" (not in the true sense of 1:1 or 1:2, but it does focus to 3 feet), and has a lot of travel to get through before it gets out to 12 feet. I have other lenses which focus faster, so you can't compare these times to other systems, only to other systems using the same lens (and shooting from my couch into my kitchen really).

Here's a screenshot of the sound "histograms"...

click to enlarge

I wouldn't be the least surprised if people more technical than myself find errors in my reasoning and my methods, so if you are one of those people, be sure to leave a comment to correct me!