Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
06-24-2008, 01:18 PM   #1
Pentaxian
konraDarnok's Avatar

Join Date: Aug 2007
Photos: Albums
Posts: 962
Tamron 300mm f/2.8 + Pentax AF 1.7x teleconverter update. . .Gawd!

What's the deal Pentax?

I haven't been super pleased with the Tamron 300mm f/2.8 + Pentax AF 1.7x combination. It just wasn't sharp -- but then I wasn't sure what to expect anyway with this setup.

My K10D has that damned back focus crap -- but I calibrated it with my FA 50mm f/1.4 to +60um in the debug menu -- which made the FA 50mm uber sharp and fixed my wide angle back focus problems with my 18-250mm.

I was pleased. Now, I started playing with the focus adjustment for the Tamron 300mm f/2.8 + Pentax AF 1.7x combination. It likes -140um! Gawd.

I don't get this crap -- either the image is at maximum contrast or it's not, or the camera doesn't have enough contrast to focus. . . but apparently it's not that simple to understand.

Anyway, check out the below picture with the Tamron 300mm f/2.8 + Pentax AF 1.7x combination when it's properly adjusted -- head is full pixel.

That's sharp, too bad I need to get in the debug menu every time I want to use this lens.

Attached Images
View Picture EXIF
PENTAX K10D  Photo 
06-24-2008, 01:36 PM   #2
Veteran Member
vizjerei's Avatar

Join Date: May 2007
Location: Toronto
Photos: Gallery
Posts: 1,418
well not only the camera body will have backfocus issue.. lens has too. So it can be your 300mm has backfocus also, no?
06-24-2008, 01:37 PM   #3
Pentaxian
konraDarnok's Avatar

Join Date: Aug 2007
Photos: Albums
Posts: 962
Original Poster
QuoteOriginally posted by vizjerei Quote
well not only the camera body will have backfocus issue.. lens has too. So it can be your 300mm has backfocus also, no?
Yea. I'm gonna think about that too. And the Tamron adjustment is -140um, a front focus situation.

Last edited by konraDarnok; 06-24-2008 at 01:42 PM.
06-25-2008, 06:35 PM   #4
Pentaxian
konraDarnok's Avatar

Join Date: Aug 2007
Photos: Albums
Posts: 962
Original Poster
It's not the tamron. It likes the +60um setting too. It's the teleconverter.

Any insights on how to fix this?

10-25-2008, 12:18 PM   #5
Pentaxian
konraDarnok's Avatar

Join Date: Aug 2007
Photos: Albums
Posts: 962
Original Poster
Fixed!

Here is the link to the incorrect optical formula that I used when reassembling the teleconverter.

http://kmp.bdimitrov.de/teleconverters/_optics/1.7.jpg

Here's an attached picture showing the correct orientation.




If you install the elements as show by Bojidar Dimitrov, the Teleconverter will front focus badly.
10-25-2008, 12:51 PM   #6
Veteran Member
sewebster's Avatar

Join Date: Jun 2008
Location: Vancouver, BC
Photos: Gallery
Posts: 533
Wow, I'm impressed that the photos looked at all reasonable with some parts backwards! Mind you, I guess you can take good photos with whole lenses backwards, so who knows...
10-26-2008, 09:08 AM   #7
Veteran Member
kristoffon's Avatar

Join Date: Aug 2008
Location: Brazil
Posts: 532
QuoteOriginally posted by konraDarnok Quote
I don't get this crap -- either the image is at maximum contrast or it's not, or the camera doesn't have enough contrast to focus. . . but apparently it's not that simple to understand.
DSLRs don't use contrast detection to focus. That's why they focus much better than compacts, and why focusing during live view sucks - the focusing sensors aren't being used.
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!
1.7x, 300mm, af, combination, f/2.8, f/2.8 pentax af, focus, k-mount, pentax, pentax lens, slr lens, tamron
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Pentax DA 55-300mm vs Tamron 70-300mm at long end (brickwall) tcdk Pentax SLR Lens Discussion 17 11-15-2009 12:52 AM
Tamron 70-300mm, Tamron 75-300mm, or Pentax 80-320mm? ajtour Pentax SLR Lens Discussion 6 06-02-2008 11:24 PM
teleconverter for Pentax FA J 75-300mm joep Pentax SLR Lens Discussion 2 03-24-2008 03:27 AM



All times are GMT -7. The time now is 11:29 PM. | 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