Forgot Password
Pentax Camera Forums Home

Show Printable Version Search this Thread
09-17-2016, 04:18 PM   #1
Senior Member

Join Date: Feb 2012
Location: Iowa
Posts: 126
PDAF with stacked teleconverters

Hi Pentaxians,

I have two Kenko pz af 1.5x SHQ teleconverters and both work fine with 60-250 on K5.

The problem is when I stack them, where K5 can not focus using viewfinder (PDAF) unless the subject is far (~100 m at 250 mm). But using the Live View (CDAF) AF works well at any distance.

Is this normal?


09-17-2016, 04:39 PM   #2
Veteran Member
MadMathMind's Avatar

Join Date: Dec 2013
Location: Houston, TX
Photos: Gallery
Posts: 1,717
PDAF generally doesn't work with f/8, except with special sensors. Canon makes a big deal out of that in their marketing for the 5D Mark IV. It's not a matter of light. It's a matter of aperture doing I forget what but the sensors just don't work.

CDAF just moves the lens around until it finds a good spot so it doesn't care about anything except the amount of light.
09-17-2016, 05:11 PM   #3
Site Webmaster
Adam's Avatar

Join Date: Sep 2006
Location: Arizona
Photos: Gallery | Albums
Posts: 49,678
Yup, this is normal. Even without TC's, a F8 lens would really struggle to focus.

Adam Webmaster (Site Usage Guide | Site Help | My Photography) server and development costs are user-supported. You can help cover these costs by donating. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, KEH, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:


  • 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!
af, camera, dslr, k-5, k-5 ii, k-5 iis, k5, pdaf, pentax k-5, teleconverters
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Similar Threads
Thread Thread Starter Forum Replies Last Post
Issue with 16 bit Pixel Shift Stacked image btnapa Pentax K-1 37 06-08-2016 04:46 PM
DA*60-250 with stacked HD DA 1.4 TC and F1.7 AF adapter stacked to get to 600mm normhead Pentax SLR Lens Discussion 41 04-19-2016 07:07 PM
Macro Failure to capture With K-x and stacked lenses smf Photographic Technique 21 01-08-2015 01:25 PM
Night August Supermoon, FA* 645 300mm + stacked teleconverters vectrln Post Your Photos! 2 08-14-2014 04:14 PM
Correct Sequence of Teleconverters (Metering With Teleconverters) MMurphy37 Troubleshooting and Beginner Help 19 09-18-2012 05:20 PM

All times are GMT -7. The time now is 04:58 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]