Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
05-20-2021, 09:00 AM   #31
Otis Memorial Pentaxian
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 42,007
QuoteOriginally posted by jumbleview Quote
If lens (like 18-135mm for example) has scale marking 35 and next one 50. And suppose you put the zoom in the middle. What would be actual focal length? 42.5? 43?. Camera reports 40 actually. Moving further to the long end it is even more confusing.
...and if the only values reported in between are 40 and 45? There is no end to this.

If you really want the feature, buy the camera that has it. If you think it is a good feature to add, post in the Product Suggestions and Feedback forum. While Ricoh does not monitor Pentax Forums, the site owners are sometimes asked about desired features or problems. That is where they go when they make their list.

Product Suggestions and Feedback - PentaxForums.com


Steve

05-21-2021, 12:46 AM   #32
Moderator
Not a Number's Avatar

Join Date: Mar 2012
Location: Venice, CA
Posts: 10,509
The only AF zoom I have is the DA 18-55mm kit lens. The zoom length is reported in zones or steps. For instance it goes from 55mm to 50mm and then from 50 to 45mm without anything between. No 54, 53, 52, 51 or 49, 48, 47 or 46mm. There is no 50mm mark on the lens but so what if I have the zoom set at 48mm the EXIF and INFO display is going report 45mm.

So eyeballing the zoom FL from the lens markings can actually be more accurate than what the electronics report.
05-21-2021, 01:07 AM   #33
Pentaxian




Join Date: Jan 2018
Location: Jersey C.I.
Posts: 3,573
Factor in the concept of "focus breathing", where the effective focal length of the lens depends, to a degree, on the distance to the subject, and the whole concept becomes fairly academic
I have a Tamron a/f 18-200mm, also a selection of primes, by the same manufacturer, covering many of the same focal lengths.
Other than at infinity, the coverage by the one, set at a specific focal length, often only compares to coverage by a prime of the same focal length, at a fairly basic level … well within the variance incurred by the range of options presented by the camera(s)!
05-21-2021, 07:07 AM   #34
Site Supporter
Site Supporter
jumbleview's Avatar

Join Date: May 2012
Location: Concord, CA
Posts: 1,066
Original Poster
QuoteOriginally posted by kypfer Quote
Factor in the concept of "focus breathing", where the effective focal length of the lens depends, to a degree, on the distance to the subject, and the whole concept becomes fairly academic
I am really glad of starting this thread. I get some actual knowledge how focal distance is reported by lens, find out about its limitation, and get useful tip on how dynamically to display zoom factor (with all its limitation of course) on KP. Thanks to everybody for participation in this discussion.

05-21-2021, 08:12 AM   #35
Otis Memorial Pentaxian
stevebrot's Avatar

Join Date: Mar 2007
Location: Vancouver (USA)
Photos: Gallery | Albums
Posts: 42,007
QuoteOriginally posted by kypfer Quote
Factor in the concept of "focus breathing", where the effective focal length of the lens depends, to a degree, on the distance to the subject, and the whole concept becomes fairly academic
Yep...rare is the lens with same angular FOV close-up as at infinity.


Steve
05-21-2021, 12:27 PM   #36
Veteran Member




Join Date: Dec 2016
Location: Southeastern Michigan
Posts: 4,508
QuoteOriginally posted by vonBaloney Quote
Zooms can be particularly prone to focus breathing, so except at infinity even an "accurate" number is often not very indicative of the actual angel of view you are getting on your subject.
Oh so true!

If I am going to compare any aspect, even with another lens, I try to be sure the framing of the shot is the same. I do this by noting what is appearing at the edges of the frame, and seeing to it that it will be the same in the comparative shot. This would mostly negate the effects of focus breathing, and provide a difference, if any, that is meaningful in real life shooting.

Last edited by mikesbike; 05-21-2021 at 12:34 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!
camera, k-mount, pentax, pentax lens, slr lens, view
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Battery life with info display off versus on gavinhw Pentax K-1 & K-1 II 10 07-26-2018 11:44 PM
unable to display image on back display Starwars50 Pentax K-3 & K-3 II 4 06-24-2015 02:48 AM
New lens doesn't have a name in info jeantree Pentax SLR Lens Discussion 13 01-08-2015 12:00 AM
Display Data doesn't shuts down bethtphotos Pentax DSLR Discussion 2 10-24-2009 02:17 PM
Why doesn't Pentax make a camera that uses another manufactures lens mount? steffi Pentax DSLR Discussion 44 04-18-2007 08:14 AM



All times are GMT -7. The time now is 10:05 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