[hannling]

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!

[Rimfiredude]

How can that be? Are you manually focusing?

[hannling]

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.

[jatrax]

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.

[Na Horuk]

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

[Rimfiredude]

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.

[hannling]

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 ----------

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.