Forgot Password
Pentax Camera Forums Home
 

Reply
Show Printable Version Search this Thread
04-04-2015, 11:35 AM   #1
New Member




Join Date: Dec 2013
Photos: Gallery
Posts: 9
Pentax DA 35/2.4 back focus problem?

I recently bought one 35/2.4 lens to use on my K5II camera. I found a problem that is when you focus with viewfinder, there is back focus problem. The further away you focus, the more severe back focus problem. However, if I use the LCD screen to focus, there seems to be no back focus problem and image looks very sharp. Does anybody else have similar problem? Is this because I got a bad copy of the lens or it's my camera's problem?

Hope someone can tell me the answers. Thanks!

04-04-2015, 11:43 AM   #2
Veteran Member
Rimfiredude's Avatar

Join Date: Oct 2014
Location: Washington
Photos: Gallery
Posts: 2,177
How can that be? Are you manually focusing?
04-04-2015, 11:59 AM   #3
New Member




Join Date: Dec 2013
Photos: Gallery
Posts: 9
Original Poster
QuoteOriginally posted by Rimfiredude Quote
How can that be? Are you manually focusing?
No. I use auto focus. I know that focusing with viewfinder and screen are using different algorithms and focusing with screen is slower but tend to be more accurate. But back focus is a different thing.
04-04-2015, 12:32 PM   #4
Site Supporter
Site Supporter
jatrax's Avatar

Join Date: May 2010
Location: Washington Cascades
Photos: Gallery | Albums
Posts: 12,316
Your camera has three different focusing systems:
  • The matte glass focusing screen used to manually focus, adjusted by setting the diopter in the camera
  • The liveview focusing which uses the sensor itself and has no adjustment
  • The viewfinder autofocus which can be adjusted using the AF fine tuning facility built into the camera.
If the Liveview focusing is correct then there is no issue with the lens but it might need an AF fine tune to work with your camera.


This might help: Fixing Front and Back Focus - Introduction - In-Depth Articles


On my k-5IIs I adjusted the AF fine tuning for about half of my lenses, on the k-3 all but 1 were too close to call. Supposedly this is caused by manufacturing tolerances between camera and lens. If both are right on, or off in different directions so that it cancels you have a 'good copy' other wise you might be off a bit and need calibration. But that same 'good copy' lens might be terrible on a different body. All modern high end DSLRs (that I know of) now provide the ability to fine the AF.

04-04-2015, 01:36 PM   #5
Pentaxian
Na Horuk's Avatar

Join Date: Feb 2012
Location: Slovenia, probably
Photos: Gallery | Albums
Posts: 11,183
QuoteOriginally posted by jatrax Quote
If the Liveview focusing is correct then there is no issue with the lens but it might need an AF fine tune to work with your camera.
Yep, this is the big one. In live view, camera uses Contrast Detect AF, which can focus on "the wrong" object, but it will always focus on the most contrasty object, exactly perfectly, no FF or BF.
The "normal" AF in DSLRs is Phase Detect. This system is the traditional AF system for SLR cameras and it is faster than CD AF, but there is a chance that it will consistently misfocus with a given lens. This is usually because the lens and camera are on other ends of factory tolerances.
What you are looking for is AF adjustment. There is an in-camera option for this. There are many threads and blog posts about it, there are different techniques, and focus charts available. If this AF adjustment cannot fix it, then you need to send the camera and lens to a service centre so they calibrate them. Or you can just replace the lens and hope it will jive better with your camera.
All brands of DSLR cameras have the AF adjustment function. If you want to buy a camera that will not need that, you will have to spend money on something like Leica gear. And even then, pros send their gear to get it all calibrated every once in a while. For most of us, learning the tricks of AF and using AF adjustment is enough.

Oh, and my DA 35mm has no AF problems, but I usually use it on my K-01 in live view anyway
04-04-2015, 02:06 PM   #6
Veteran Member
Rimfiredude's Avatar

Join Date: Oct 2014
Location: Washington
Photos: Gallery
Posts: 2,177
QuoteOriginally posted by hannling Quote
No. I use auto focus. I know that focusing with viewfinder and screen are using different algorithms and focusing with screen is slower but tend to be more accurate. But back focus is a different thing.
Hmmmm...That is quite interesting.
04-04-2015, 07:04 PM   #7
New Member




Join Date: Dec 2013
Photos: Gallery
Posts: 9
Original Poster
QuoteOriginally posted by jatrax Quote
Your camera has three different focusing systems:
  • The matte glass focusing screen used to manually focus, adjusted by setting the diopter in the camera
  • The liveview focusing which uses the sensor itself and has no adjustment
  • The viewfinder autofocus which can be adjusted using the AF fine tuning facility built into the camera.
If the Liveview focusing is correct then there is no issue with the lens but it might need an AF fine tune to work with your camera.


This might help: Fixing Front and Back Focus - Introduction - In-Depth Articles


On my k-5IIs I adjusted the AF fine tuning for about half of my lenses, on the k-3 all but 1 were too close to call. Supposedly this is caused by manufacturing tolerances between camera and lens. If both are right on, or off in different directions so that it cancels you have a 'good copy' other wise you might be off a bit and need calibration. But that same 'good copy' lens might be terrible on a different body. All modern high end DSLRs (that I know of) now provide the ability to fine the AF.
Thanks, I will try the fine tuning. Glad to hear that the lens has no problem, so I don't need to change it.

---------- Post added 04-04-15 at 07:04 PM ----------

QuoteOriginally posted by Na Horuk Quote
Yep, this is the big one. In live view, camera uses Contrast Detect AF, which can focus on "the wrong" object, but it will always focus on the most contrasty object, exactly perfectly, no FF or BF.
The "normal" AF in DSLRs is Phase Detect. This system is the traditional AF system for SLR cameras and it is faster than CD AF, but there is a chance that it will consistently misfocus with a given lens. This is usually because the lens and camera are on other ends of factory tolerances.
What you are looking for is AF adjustment. There is an in-camera option for this. There are many threads and blog posts about it, there are different techniques, and focus charts available. If this AF adjustment cannot fix it, then you need to send the camera and lens to a service centre so they calibrate them. Or you can just replace the lens and hope it will jive better with your camera.
All brands of DSLR cameras have the AF adjustment function. If you want to buy a camera that will not need that, you will have to spend money on something like Leica gear. And even then, pros send their gear to get it all calibrated every once in a while. For most of us, learning the tricks of AF and using AF adjustment is enough.

Oh, and my DA 35mm has no AF problems, but I usually use it on my K-01 in live view anyway
Thanks! Will try fine tuning.
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!
adjustment, af, back focus problem, camera, cameras, focus, gear, k-mount, lens, object, pentax 35mm f/2.4, pentax da, pentax lens, slr lens, system, view
Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
DA 50 1.8 and DA 35 2.4 on sale @ Pentax store online ranjitacharya Pentax Price Watch 61 12-09-2014 04:14 PM
DA 35 2.4 Stiff Focus london.paul1 Pentax SLR Lens Discussion 6 09-25-2014 05:53 AM
For Sale - Sold: Pentax DA-L 35 f/2.4 zbrueningsen Sold Items 3 08-02-2013 03:41 AM
PENTAX DA* 55mm 1.4 Focus Problem wmf2012 Troubleshooting and Beginner Help 4 07-22-2013 03:26 PM
DA 12-24 back-focus problem gattofix Pentax SLR Lens Discussion 14 07-28-2009 09:10 AM



All times are GMT -7. The time now is 07:11 PM. | 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