Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
11-26-2016, 04:29 PM   #16
Des
Loyal Site Supporter
Des's Avatar

Join Date: Jan 2014
Location: Sth Gippsland Victoria Australia
Photos: Albums
Posts: 2,015
QuoteOriginally posted by audiobomber Quote
note that the screw drive DA 55-300mm is an IF lens
Have we got different definitions of internal focus? Here's mine (from Wikipedia):
"An internal focus lens (sometimes known as IF) is a photographic lens design in which focus is shifted by moving the inner lens group or groups only, without any rotation or shifting of the front lens element. "
Zoomed to 300mm, the barrel length on my DA-L 55-300 changes by about 17mm when the focus ring is turned from one end to the other (that is, the front element moves fore and aft in focusing). That's not an internal focus lens by my definition.

That's not to say that this lens has the ideal FOV for the particular focal length regardless of distance to subject. But it's ahead of other tele zooms I've used (Tamron 18-250, Sigma 170-500 and DA 18-135). For the typical application of photographing smallish birds/animals at say 3m to 10m, the actual magnification is a significant advantage of the screw-driven 55-300 models over other zooms.


Last edited by Des; 11-26-2016 at 07:32 PM.
11-27-2016, 09:53 AM   #17
Pentaxian
audiobomber's Avatar

Join Date: May 2008
Location: Sudbury, Ontario
Photos: Albums
Posts: 6,686
QuoteOriginally posted by Des Quote
Have we got a different definition of internal focus? Here's mine (from Wikipedia):
"An internal focus lens (sometimes known as IF) is a photographic lens design in which focus is shifted by moving the inner lens group or groups only, without any rotation or shifting of the front lens element. "
Zoomed to 300mm, the barrel length on my DA-L 55-300 changes by 17mm when the focus ring is turned from one end to the other (that is, the front element moves fore and aft in focusing). That's not an internal focus lens by my definition.
Sorry, you are correct. It is not an IF lens. It does however lose range as focus distance decreases, which means the internal elements are shifting. When I have time later this week I intend to do a test showing this with the A 135mm, which does not change focal length at MFD.
04-06-2017, 12:42 PM   #18
Senior Member
BATMON's Avatar

Join Date: Aug 2013
Posts: 162
What's the DA 4-5.8 55-300mm ED WR "Sweet Spot"?
04-09-2017, 06:29 PM   #19
Des
Loyal Site Supporter
Des's Avatar

Join Date: Jan 2014
Location: Sth Gippsland Victoria Australia
Photos: Albums
Posts: 2,015
QuoteOriginally posted by BATMON Quote
What's the DA 4-5.8 55-300mm ED WR "Sweet Spot"?
It depends what focal length you use, and whether centre sharpness or edge sharpness is the priority.

See this test of the pre-WR version (optically identical, except for the improved coatings on the later version):
Pentax SMC DA 55-300mm f/4-5.8 ED - Review / Test Report
On this test, f8 gave the best centre sharpness at each tested point up to 300mm, when it was shaded by f11. For more even resolution across the frame at the wide end (say 55-100mm), f11 was better, at the cost of a little centre sharpness.

Tests like this aren't gospel (it's just one sample after all) but they give a general indication. As a general rule consumer zooms like this always do better stopped down a bit. With the DA-L version I generally try to stop down one or two stops, unless I want the wider aperture for more light or shorter DOF. At 300mm I try to use f8 (or up to f11) if the light is good enough. But f7.1 is OK too.


Last edited by Des; 04-10-2017 at 07:40 PM.
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!
300mm, 55-300mm, autofocus, breathing, da, focus, k-mount, length, lens, magnification, mfd, pentax lens, review, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Pentax 55-300 WR vs Sigma 70-300 APO Macro keanex Pentax SLR Lens Discussion 21 06-22-2016 12:12 PM
HD 55-300 vs DA 55-300 csa Pentax SLR Lens Discussion 17 03-14-2015 06:31 PM
which 55-300 lens? Barry Hall Pentax SLR Lens Discussion 22 03-27-2013 01:22 PM
Which to buy? FA 100-300 4.7-5.8, or 55-300 DA-L? GibbyTheMole Pentax SLR Lens Discussion 19 03-15-2011 07:15 AM
18-55 II, 18-250, & 55-300, and last APO 70-300 LeDave Pentax SLR Lens Discussion 3 07-12-2009 09:51 PM



All times are GMT -7. The time now is 11:53 AM. | 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