Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
07-18-2013, 02:40 PM   #1
Junior Member




Join Date: Jul 2013
Posts: 35
Wrong aperture communication?

Hello,

I have an issue with a 3rd party manual lense on my Pentax K100D. It is an Exakta 28mm Macro lense with A setting. It has an aperture range from 2.8 to 22. However, when putting it to A and controlling the aperture in AV mode I can set it to all values between 1.4 and 22.

Did anybody observe something similar and can explain, what could be the reason?

Thanks,

Jim

07-18-2013, 03:04 PM - 1 Like   #2
Veteran Member
scratchpaddy's Avatar

Join Date: Feb 2013
Location: Phoenix
Posts: 2,360
Your lens was secretly a f/1.4? Score!

Seriously, though: the lens tells the camera its aperture range via a binary code created by the contacts on the lens mount. If a contact is conductive (metal), it's a 1. If it's an insulator (plastic) it's a zero. Look at the chart halfway down the page here:

Features and Operation of the Ka Mount

The code your lens is supposed to transmit is 011*10 (the * is the contact that tells the camera it's dealing with an A lens), which means f/2.8-22. The code the camera is getting is 111*10, which means f/1.4-22.

The contact closest to the bottom of the lens, furthest from the red mounting dot, is supposed to be an insulator on your lens (0), but the camera is seeing it as conductive (1). Clean it and see what happens. If that fails, put a little piece of tape over that last contact.
07-19-2013, 12:15 AM   #3
Junior Member




Join Date: Jul 2013
Posts: 35
Original Poster
QuoteOriginally posted by scratchpaddy Quote
Your lens was secretly a f/1.4? Score!

Seriously, though: the lens tells the camera its aperture range via a binary code created by the contacts on the lens mount. If a contact is conductive (metal), it's a 1. If it's an insulator (plastic) it's a zero. Look at the chart halfway down the page here:

Features and Operation of the Ka Mount

The code your lens is supposed to transmit is 011*10 (the * is the contact that tells the camera it's dealing with an A lens), which means f/2.8-22. The code the camera is getting is 111*10, which means f/1.4-22.

The contact closest to the bottom of the lens, furthest from the red mounting dot, is supposed to be an insulator on your lens (0), but the camera is seeing it as conductive (1). Clean it and see what happens. If that fails, put a little piece of tape over that last contact.
Thanks a lot - great ressource!

Putting a tape over the contact really worked. So I now need to see if this works in a longer run or if I need to insulate it in a different way!
Reply

Bookmarks
  • 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!
aperture, lense, pentax help
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Pentax-A 50mm f1.4 sometimes sets wrong aperture when using "A"-setting qwertyazerty Troubleshooting and Beginner Help 6 05-02-2013 09:30 AM
Anyway to set aperture of the Tamron 70/200 f2.8 / got the wrong asapter for my Q mgbirder Pentax Q 3 12-14-2012 02:06 PM
K-5 reporting wrong aperture for A setting atekant Troubleshooting and Beginner Help 8 10-17-2012 12:29 PM
Playing with aperture: am I doing it wrong? Balog Troubleshooting and Beginner Help 3 02-02-2011 09:41 AM
K100D registers wrong aperture Timarete Pentax DSLR Discussion 18 06-07-2008 12:59 PM



All times are GMT -7. The time now is 02:41 AM. | See also: NikonForums.com, CanonForums.com 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?
register
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]
Top