Forgot Password
Pentax Camera Forums Home

Show Printable Version Search this Thread
07-17-2010, 05:30 AM   #1
Junior Member

Join Date: May 2010
Location: *
Photos: Gallery | Albums
Posts: 45
question on WR 50-200mm/2 Q's


Last edited by TheoSixx; 07-19-2010 at 08:13 AM. Reason: *****
07-17-2010, 05:35 AM   #2
Site Webmaster
Adam's Avatar

Join Date: Sep 2006
Location: Arizona
Photos: Gallery | Albums
Posts: 43,118
50x1.5 = 75
200x1.5 = 300

Looks like you multiplied your numbers twice or multiplied instead of dividing!

If you want to calculate FOV, you multiply the focal length by 1.5 when going from APS-C to Full-Frame, and divide by 1.5 when going from Full-Frame to APS-C. Keep in mind that a 200mm lens is always a 200mm lens, however, and that the calculations above are only to show what focal length on a FF body would result in the same FOV on APS-C.

Adam Webmaster (Site Usage Guide | Site Help | My Photography)'s high server and development costs are user-supported. You can help cover those costs by donating. Or, buy your photo gear from our affiliates, Adorama, B&H Photo, or Topaz Labs, and get FREE Marketplace access - click here to see how! Trusted Pentax retailers:

07-18-2010, 08:06 AM   #3
B&H Photo Specialist
Chuck-B&H's Avatar

Join Date: May 2010
Location: New York
Posts: 866

Focal length causes so much confusion today, due in part I believe because 35mm film cameras evolved into digital. The issue has always been around, but in the past, we all just accepted that an 80mm lens was a normal (50mm) lens on a Hasselblad.

The first is the technical description of the optical formula used in the lens design.

Focal length is defined as the distance between the film or sensor area (known as the focal plane) and the optical center or nodal point of a lens focused at infinity. So a 50mm lens’s optical center would be 50mm’s from the film or sensor plane at infinity.

The second is our interpretation of what the lens will do for us while photographing.

We describe a 50mm lens as being a normal lens. “Normal” lenses have focal lengths approximately equal to the diagonal length of the film or sensor area. The diagonal length of 35mm film is 42mm’s. Normal lens have an angle of coverage of approximately 46 degrees, which corresponds to our own vision.

The lens multiplier formula used today is method for understanding how a lens will perform on a digital camera ( with a sensor smaller than a 35mm film frame ) in terms of what we were accustomed to when shooting film. Whether on an APS-C sensor, Full Frame or 35mm film body, a 50mm lens is a 50mm lens. How it affects our image is another matter.

C h u c k C a p r i o l a
Live Chat and E-Mail Sales Manager B&H Photo-Video

Thank you, we appreciate your business.
*** Peace on Earth ***

Last edited by Chuck-B&H; 07-18-2010 at 08:07 AM. Reason: Spacing

  • Submit Thread to Facebook Facebook
  • Submit Thread to Twitter Twitter
  • Submit Thread to Digg Digg
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Similar Threads
Thread Thread Starter Forum Replies Last Post
Some Newbie Q's about K7 jayendra Pentax DSLR Discussion 11 09-14-2010 12:23 PM
noob HDR Q's lodi781 Photographic Technique 6 03-06-2008 04:16 PM
Flash Q's - 360fgz + M mode for fill and Pentax DSLR Discussion 10 06-24-2007 11:09 PM
some Q's with a lens i wuld like to buy Kennytdfer Pentax SLR Lens Discussion 14 02-28-2007 03:51 AM

All times are GMT -7. The time now is 05:27 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]