Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
05-13-2007, 11:41 AM   #1
Senior Member




Join Date: Sep 2006
Location: Tartu, Estonia
Posts: 159
Question to DFA 100 owners

Hi everyone! Posted it already at dpreview but as my experience shows I can get more expertize on this forum :-)
When I use my DFA 100/2.8 for non-macro work (that is try to use autofocus without clamp engaged) it behaves very strange IMO on my K100D/K10D: if object is more than 2 meters (approx.) away it always drives to false direction up to limit and only then drives focus back to the right direction and then focuses OK (but much worse than my other FA/DA glass). Has anyone experienced such a behavior and is it possible that I have got a lemon? Last option would be very disappointing as the macro season here has just begun and our supplier is out of stock :-(
Best and happy shooting, JR

05-13-2007, 01:36 PM   #2
Ole
Administrator
Ole's Avatar

Join Date: Sep 2006
Location: Copenhagen, Denmark
Photos: Gallery | Albums
Posts: 3,917
A macro has a very long throw of the focusing mechanism. If it initially is far from being in focus you will see the behaviour which you describe - due to low contrast when the image is extremely blurred the camera cannot detect the correct direction to turn the focusing ring. The old 100mm FA macro lens had a focus limiter to help prevent this behaviour.

I noticed a similar pattern yesterday with my 300mm/4.5 when initially set way off focus.

My take is that your lens is OK.
05-13-2007, 02:22 PM   #3
Senior Member




Join Date: Sep 2006
Location: Tartu, Estonia
Posts: 159
Original Poster
Thanks Ole

but if my glass is behaving erratically even on a sunny day with properly aligned contrasty object? Did some tests on tripod- when I use manual de-focusing with test chart it still has no clue which way to move- all my other DA/FA glass hesitate a fraction and then drive focus to appropriate direction- but not this one And BTW I have experienced moments when clamp is OFF (ie AF mode) that if I try to rotate the focus ring it refuses to change focus- but it ought to be a quick-shift one?
OK, too many questions and too few solutions...
Best and happy shooting and sharing Your experience to everyone, JR
05-13-2007, 02:38 PM   #4
Ole
Administrator
Ole's Avatar

Join Date: Sep 2006
Location: Copenhagen, Denmark
Photos: Gallery | Albums
Posts: 3,917
I just checked my D FA 100/2.8.

Distance to object: 3 meters. Indoors, 100 ISO 1/10 sec f/2.8.

If the lens is pre-focused between 1 meter and infinity it snaps into focus right away.

If the lens is pre-focused at 70 cm it travels all the way to closest focusing distance, then out again and snaps into focus.

It doesn't help that the object is high contrast. When it is extremely much out of focus there is no contrast in the image formed on the autofocus sensor (and in the viewfinder) anyway.

Your other DA and FA lenses are not macro lenses - they don't have the same very long distance of travel from close focus to infinity as the macro does. That's probably why they "behave better".

05-14-2007, 12:05 AM   #5
Senior Member




Join Date: Sep 2006
Location: Tartu, Estonia
Posts: 159
Original Poster
Thank You!

Your answer was of great relief to me So my glass is OK and I can continue shooting without worries and whining.
Best and happy shooting, JR
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!
dfa, direction, drives, k-mount, pentax lens, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
For Sale - Sold: Dfa 100 2.8 wr (conus) DogLover Sold Items 1 07-08-2010 09:48 AM
DFA 100 macro's reviews Ash Pentax SLR Lens Discussion 14 09-21-2009 09:20 AM
DFA 100 F2.8 Macro Question mikeatnite Pentax SLR Lens Discussion 3 04-26-2008 05:54 PM
Grandson with DFA 100 Mallee Boy Post Your Photos! 6 04-06-2007 06:01 PM



All times are GMT -7. The time now is 12:23 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