Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
07-27-2012, 02:43 PM   #1
Veteran Member




Join Date: Jan 2012
Location: NE, USA
Posts: 1,302
How do you focus for IR?

The modern lenses have no IR compensation setting on the focus scale. How should I figure IR compensation?

If I focus at something that is 3 feet away, should I set the focus at 4 feet or 2 feet or what?

Thanks

07-27-2012, 03:35 PM   #2
Site Supporter




Join Date: Sep 2006
Location: midwest, United States
Photos: Gallery
Posts: 3,329
If your camera has lv use that. Some cameras will af ir if the proper filter is used to get rid of daylight. If manual focusing close lens down for more dof and test focus with multiple shots.
thanks
barondla
07-27-2012, 03:47 PM   #3
Veteran Member




Join Date: Jan 2012
Location: NE, USA
Posts: 1,302
Original Poster
I don't have any live view. Hard to tell until I get it up on the screen. Wondered if there is some sort of forumla for IR correction?
07-27-2012, 04:02 PM   #4
Moo
Senior Member




Join Date: Jun 2008
Posts: 174
Lenses used to have focus marks for IR. New ones may have no markings at all...
You may be able to work out your own formula though, by trial and error, which is quick and free with digital
I expect it depends what IR wavelength you are working with too.

07-27-2012, 04:23 PM   #5
Site Supporter
gofour3's Avatar

Join Date: Oct 2008
Location: Vancouver, Canada
Posts: 5,345
The IR focusing shift will be different for each lens/focal length. I would tend to use an old MF Pentax lens.

Phil.
07-27-2012, 05:09 PM   #6
Inactive Account




Join Date: Dec 2008
Location: Ames, Iowa, USA
Photos: Albums
Posts: 2,965
Your IR photos (that I've seen) have been in focus.

If your system autofocuses ok, then manual focus should be ok too if you rely on the CIF beep & green hexagon to detect focus because that's the way autofocus does it..

Otherwise, how did you get such good focus so far?

You could also change the shims on the viewfinder screen so that viewfinder focus agrees with actual focus. Mount an old lens with the red IR focus mark, then focus on infinity (set to the IR mark), then adjust the focus screen shims until the scene is in focus through the viewfinder.

The best way would be to get & convert a live view camera - then there'd be no problems with setting white balance, getting precise focus, etc. I don't know which Pentax models were the first with live-view.

Dave in Iowa
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!
compensation, feet, focus, ir, pentax help
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Focus, Focus, Focus (or the usefulness of focus charts) GoremanX Pentax DSLR Discussion 31 12-21-2014 11:49 AM
K-5 Manual Lens Front Focus & Focus Beep woes fixed kneonx Pentax K-5 14 04-12-2014 03:47 PM
10 Reasons why manual focus primes are better than those new auto focus zoom lenses JoepLX3 Pentax SLR Lens Discussion 188 07-25-2012 03:28 PM
Focus Ring on DA 35 macro makes a clicking noise; manual focus ... this normal? eadrian75 Pentax SLR Lens Discussion 2 04-12-2011 12:51 AM
Confirm my understand of metering w/ manual lenses focus hyperfocal focus DeadJohn Pentax SLR Lens Discussion 4 03-25-2011 12:31 PM



All times are GMT -7. The time now is 07:34 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