Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
10-12-2008, 06:12 PM   #1
Site Supporter




Join Date: Mar 2008
Location: North Carolina
Photos: Gallery
Posts: 466
Setting focus for infinity question?

I have a prime lens that is a little off on the infinity focus, ie infinity is in focus before the lens hits the mechanical stop(which is better than the other way) however, I would like the lens to hit the stop and be in focus for infinity at the same time. If I wanted to adjust the lens, how distant an object would I need to focus on for an accurate setting for infinity?

I am shooting with a k100d super and 400mm prime.

Thanks
7.62lew

10-12-2008, 08:43 PM   #2
Loyal Site Supporter
Canada_Rockies's Avatar

Join Date: Nov 2007
Location: Sparwood, BC, Canada
Photos: Gallery | Albums
Posts: 9,142
QuoteOriginally posted by 7.62lew Quote
I have a prime lens that is a little off on the infinity focus, ie infinity is in focus before the lens hits the mechanical stop(which is better than the other way) however, I would like the lens to hit the stop and be in focus for infinity at the same time. If I wanted to adjust the lens, how distant an object would I need to focus on for an accurate setting for infinity?

I am shooting with a k100d super and 400mm prime.

Thanks
7.62lew
I think you will find that most, if not all, long focal length lenses allow for focusing past the infinity mark. I have read somewhere that the length of the barrel of the lens extends when the lens is hot, and infinity moves away from the camera a small but measurable amount. I also understand that reflex lenses (mirrors) are even more prone to the problem.
10-13-2008, 08:43 AM   #3
Pentaxian
Wheatfield's Avatar

Join Date: Apr 2008
Location: The wheatfields of Canada
Posts: 10,043
QuoteOriginally posted by 7.62lew Quote
I have a prime lens that is a little off on the infinity focus, ie infinity is in focus before the lens hits the mechanical stop(which is better than the other way) however, I would like the lens to hit the stop and be in focus for infinity at the same time. If I wanted to adjust the lens, how distant an object would I need to focus on for an accurate setting for infinity?

I am shooting with a k100d super and 400mm prime.

Thanks
7.62lew
Your lens is the way it is supposed to be, for the reason Albert has given. You could probably misadjust the focusing ring to do what you want, but you would lose infinity focus when the lens is warm, and your focus distance marks would be tossed out of adjustment as well.
10-13-2008, 09:00 AM   #4
Site Supporter




Join Date: Mar 2008
Location: North Carolina
Photos: Gallery
Posts: 466
Original Poster
QuoteOriginally posted by Canada_Rockies Quote
I think you will find that most, if not all, long focal length lenses allow for focusing past the infinity mark. I have read somewhere that the length of the barrel of the lens extends when the lens is hot, and infinity moves away from the camera a small but measurable amount. I also understand that reflex lenses (mirrors) are even more prone to the problem.
QuoteOriginally posted by Wheatfield Quote
Your lens is the way it is supposed to be, for the reason Albert has given. You could probably misadjust the focusing ring to do what you want, but you would lose infinity focus when the lens is warm, and your focus distance marks would be tossed out of adjustment as well.
That makes sense. I guess the longer the lens the more "space" is given for expansion. After the lens is in focus at infinity the focus ring moves another .100" past infinity (and out of focus) on the sigma 400MM, while on the sigma 24mm it hits the stop and it is still in focus. Probably very little expansion on a 24mm, hence not the requirement for a large buffer.

Thanks, I will leave well enough alone.

7.62lew

10-13-2008, 10:13 AM   #5
Veteran Member
tomtor's Avatar

Join Date: Apr 2008
Location: Netherlands
Posts: 382
QuoteOriginally posted by 7.62lew Quote
I have a prime lens that is a little off on the infinity focus, ie infinity is in focus before the lens hits the mechanical stop(which is better than the other way) however, I would like the lens to hit the stop and be in focus for infinity at the same time. If I wanted to adjust the lens, how distant an object would I need to focus on for an accurate setting for infinity?

I am shooting with a k100d super and 400mm prime.

Thanks
7.62lew
As said by the others, better not to mess with the infinity stop, but you can look
up the hyperfocal distance here:

Online Depth of Field Calculator
10-13-2008, 11:30 PM   #6
Site Supporter




Join Date: Mar 2008
Location: North Carolina
Photos: Gallery
Posts: 466
Original Poster
QuoteOriginally posted by tomtor Quote
As said by the others, better not to mess with the infinity stop, but you can look
up the hyperfocal distance here:

Online Depth of Field Calculator

Thanks for the link!
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!
focus, infinity, k-mount, lens, pentax lens, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Pentax K20D & M42 Lenses Infinity Focus Question kopimorning Pentax SLR Lens Discussion 4 07-17-2010 05:56 PM
Focus at infinity veebs2 Troubleshooting and Beginner Help 16 03-06-2010 01:47 AM
focus on infinity??? debbie Pentax DSLR Discussion 4 07-02-2008 08:45 PM
Voigtlander SL lenses - Infinity focus question thePiRaTE!! Pentax SLR Lens Discussion 29 10-30-2007 10:22 AM
no infinity focus? JahJahwarrior Pentax SLR Lens Discussion 2 07-09-2007 04:58 PM



All times are GMT -7. The time now is 12:33 AM. | See also: NikonForums.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