Forgot Password
Pentax Camera Forums Home

Show Printable Version Search this Thread
07-01-2009, 08:50 AM   #1
Site Supporter
Site Supporter

Join Date: Jul 2007
Location: houston texas
Photos: Albums
Posts: 80
input focal length

I have a tamron 1.4 teleconverter and a sigma apo dg 170-500 lenes. When I use this combination, the camera, ask me for the input focal length. What input focal length should I use on the camera?

07-01-2009, 09:01 AM   #2
Loyal Site Supporter
Loyal Site Supporter
Canada_Rockies's Avatar

Join Date: Nov 2007
Location: Sparwood, BC, Canada
Photos: Gallery | Albums
Posts: 11,735
That is a very tough question. The problem with zoom lenses and setting SR focal lengths is a really difficult one to get around. One should really change the SR focal length every time one changes the zoom setting, but that is just not a practical solution. The trouble comes in when the selected focal length is much longer than the actual effective focal length. The SR system will overcompensate and actually come up with worse effects than if it were off.

In your case, (170*1.4 = 238) would be the minimum setting and 700mm the maximum. When I use my 70-210, I set the SR to 100mm. It seems to work OK the few times I have used the lens at the wide end, but I really have not used it enough to be certain.

One philosophy I have considered is to set the SR to the upper end of the zoom range and turn it off when I go wide on the grounds that I am shakier at 200mm than at 100mm. The 70-210 is the only lens I have that requires this sort of guessing, so it does not come up very often in my shooting.
07-03-2009, 05:18 AM   #3
Site Supporter
Site Supporter
jmc7104's Avatar

Join Date: Feb 2008
Location: Rock Island, Illinois 61201
Photos: Gallery
Posts: 436
The only reason the camera wants the focal length is for shake reduction and if you are using a 1.4TC shooting at 500mm you should be on a tripod with sr turned off. I have the 50-500 plus 1.7TC and even shooting from the truck resting the lens on the door I turn sr off and engine also. jim

  • 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!
camera, dslr, input, length, photography
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Similar Threads
Thread Thread Starter Forum Replies Last Post
Manual Focal Length Input WhichWayIsUp? Troubleshooting and Beginner Help 11 12-15-2016 05:32 AM
Focal length input K(s)evin Pentax SLR Lens Discussion 6 10-27-2010 04:03 PM
What focal length input DutchAus Troubleshooting and Beginner Help 3 12-24-2009 09:15 AM
Input Focal Length lutzvo Photographic Technique 9 01-10-2009 02:51 PM
Input focal length for MF lenses NicholasN Pentax DSLR Discussion 2 07-16-2008 06:58 PM

All times are GMT -7. The time now is 08:39 AM. | See also:, 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?
Creating a FREE ACCOUNT takes under a minute, removes ads, and lets you post! [Dismiss]