Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
04-04-2009, 08:51 PM   #1
Forum Member




Join Date: Jun 2008
Posts: 58
Pentax 18-250mm Vs. Tamron 70-300mm, focal length markings are not the same

I was doing some test shots of both lenses at the same focal length and I noticed that 70mm on the Pentax was alot wider than 70mm on the Tamron. and likewise 250mm on the Pentax was ALOT wider than the 250mm on the Tamron.

For having the same focal length, why is the Pentax so much wider? I thought bother were built for the 1.5X crop factor, so shouldn't focal lengths be generally consistent?

04-04-2009, 09:19 PM   #2
Senior Member




Join Date: Sep 2008
Posts: 153
QuoteOriginally posted by aweir Quote
I was doing some test shots of both lenses at the same focal length and I noticed that 70mm on the Pentax was alot wider than 70mm on the Tamron. and likewise 250mm on the Pentax was ALOT wider than the 250mm on the Tamron.

For having the same focal length, why is the Pentax so much wider? I thought bother were built for the 1.5X crop factor, so shouldn't focal lengths be generally consistent?
The markings are made at infinity for IF lenses. With an IF lens, a shorter subject distance will move the focus mechanism enough to shorten the effective focal length. I have seen posts that state the 18-250mm, when used at its closest focus distance and at 250mm, in the "macro' mode, is effectively a 90mm lens.
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!
250mm, 70mm, alot, k-mount, length, pentax, pentax 18-250mm, pentax lens, slr lens, tamron
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
For Sale - Sold: Pentax 55-300mm, Tamron 18-250mm (US) opiedog Sold Items 3 10-19-2010 11:21 AM
Pentax F-1.7X AF adapter: input focal length or not? jpzk Pentax SLR Lens Discussion 43 03-17-2010 07:55 AM
focal length on camera using sigma 170-500 and tamron 1.4 af tele-converter jon pafford Pentax SLR Lens Discussion 2 03-01-2010 08:00 PM
DA★ 60-250mm Focal length and focus observation kcmadr Pentax SLR Lens Discussion 4 05-13-2009 12:51 PM
Which Pentax focal length for Macro? tscip22 Pentax DSLR Discussion 34 09-29-2008 11:38 AM



All times are GMT -7. The time now is 12:36 PM. | 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