Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
08-29-2013, 11:09 AM   #1
Site Supporter




Join Date: Jul 2009
Location: Montco, PA
Photos: Gallery | Albums
Posts: 135
Tamron 28-75 vs. 18-250 AF performance

I recently got a used K-x (my K-r is in the shop for an extended holiday) and noticed that my two most-used lenses seem to exhibit very different AF performance (as in speed) on this camera. By this I mean different from each other.

On my K-r, the two lenses behaved a bit differently depending on the lighting. In brighter light (outdoors during the day, for example, the 18-250 would get a good focus lock very quickly, but indoors, it was sluggish. The 28-75 didn't seem to focus quite as quickly in good light as the 18-250 (but it wasn't far behind), and in poorer lighting, it was much quicker and more accurate.

On the K-x, it actually seems sort of opposite, at least in bad lighting. In daylight, both seem to behave as they did on the K-r, but when shooting indoors, it seems like the 28-75 will run back and forth through the adjustment range 2 or 3 times before getting a lock. I don't think it's a matter of the subject, either. For example, the image below was taken with the 18-250 because the 28-75 just wouldn't lock onto it, and this has some pretty decent contrast to it.

And because of the constant f2.8, the 28-75 has been my "go-to" indoors lens. With this type of AF lag, though, I may need to re-evaluate things.



08-29-2013, 11:32 AM   #2
Veteran Member
crewl1's Avatar

Join Date: Jul 2010
Location: Los Angeles, CA
Photos: Gallery | Albums
Posts: 9,795
My K-x was a bit of a dog with AF indoors, even with fast lenses.

Did you test both lenses at the same focal range to see if it isn't just one was providing a more contrasty target?
08-29-2013, 12:01 PM   #3
Site Supporter




Join Date: Jul 2009
Location: Montco, PA
Photos: Gallery | Albums
Posts: 135
Original Poster
QuoteOriginally posted by crewl1 Quote
My K-x was a bit of a dog with AF indoors, even with fast lenses.

Did you test both lenses at the same focal range to see if it isn't just one was providing a more contrasty target?
The photo I posted was taken at 70mm. I tried getting the same shot, from the same position, using the 28-75 set to 75mm and it kept seeking back and forth trying to lock on the lampshade. Even on my K-r, I've had occasional issues locking at maximum FL on that lens, so I pulled it back a bit, to about 60mm and it still wouldn't lock. I should say also that the onboard flash was on for all of these shots. Maybe the K-r's focus assist lamp deserves the credit for this lens performing so well on that body?
08-29-2013, 01:02 PM   #4
Veteran Member
crewl1's Avatar

Join Date: Jul 2010
Location: Los Angeles, CA
Photos: Gallery | Albums
Posts: 9,795
Yes the AF assist light could help but also the K-r and later bodies may have improved low light focusing due to newer AF systems.

(This feature is touted highly in the K-5II.)

When I had the K-x I would usually just revert to manual AF when indoors. I eventually upgraded it to a K-5.

I have both of your lenses and they perform really well on my K-5 indoors. The AF assist light does kick in occasionally when it is fairly dark.

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!
af, focus, indoors, k-mount, k-r, k-x, lenses, light, pentax lens, performance, slr lens
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Pentax 17-70 vs. Tamron 28-75 vs. Flash mikemike Pentax SLR Lens Discussion 30 03-03-2013 09:13 AM
New Sigma 18-250 Vs Used Tamron/Pentax 18-250 regardless of the price ishchupak Pentax K-5 11 09-26-2011 01:45 AM
Superzoom comparison? Tamron 28-200 vs Pentax 18-250 vs Sigma 28-300 etc JayR Pentax SLR Lens Discussion 12 03-10-2010 12:40 PM
Tamron 28-75 f2.8 vs Pentax 18-55 kit lens ggad Pentax SLR Lens Discussion 3 02-22-2008 02:01 AM
Tamron 18-250 vs Tamron 28 - 300 Atlantafine Pentax SLR Lens Discussion 3 04-26-2007 07:50 PM



All times are GMT -7. The time now is 08:23 AM. | 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