16-50 focus hunting

**7samurai** · 10-22-2015, 10:40 AM

Just bought and returned a 16-50. It was focus hunting even under high contrast subjects. It would refuse to lock focus about 10% of the time. It would also take a number of adjustments before locking focus. (Hunting).

Before I order a replacement, I want to verify this is not normal for this lense.

**jatrax** · 10-22-2015, 10:58 AM

Not normal at all. Mine is quite reliable at locking focus, not necessarily the fastest focusing lens I own but it doesn't hunt.

However, if the SDM motor is failing it can appear to hunt but what is actually happening is the lens motor is not moving the elements correctly so the focus attempt fails. This should not be happening on a new lens as even those that had problems (prior to 2012) worked fine for a long time before issues arose.

**7samurai** · 10-22-2015, 11:20 AM

Thank you for the info. Comparing it against my 16-45, the 16-45 was very reliable and faster at focusing than the 16-50. Every focus attempt on the 16-50 included at least 5-10 adjustment of the motor before it finally aquired focus. This made it impossible to even shoot shots of my slow walking dog. I'll see how the second one goes.

K57XR · 10-22-2015, 11:36 AM

Originally posted by 7samurai

Every focus attempt on the 16-50 included at least 5-10 adjustment of the motor before it finally aquired focus.

It shouldn't do that on a regular basis. Maybe on challenging scenes? Mine runs on screw-drive and hunts once in a while but we're talking indoor poor lighting or low contrast subjects.

**david94903** · 10-22-2015, 12:39 PM

I think you were experiencing the early stages of SDM failure. My 16-50 started focus hunting more and more prior to the SDM failure. Had it repaired through CRIS, and after about six months the focus hunting began again and then a second failure. Have since disabled the SDM, and find that I don't have any focus hunting issues with the screw drive.

**7samurai** · 10-22-2015, 01:17 PM

Just ordered another one. The SDM is not inspiring confidence. If I keep the second one, might have to eBay a body to do the screw conversion. Sorry for raising the SDM issue again.

**7samurai** · 10-24-2015, 01:15 PM

Just got my 2nd copy and found another issue. The second copy is vastly improved, but when focusing in broad daylight, 50mm, f/2.8, and a black shirt, it will not focus. Tried it 20 times and no luck. Stop down to f/3.2, or shorten to 40mm and it seems to focus more often. I know it's difficult conditions but the 50-135 has no issues and is very snappy. Faster than my screw drives. I'm wondering if I'm hitting the limit of the f/2.8 focus sensor.

Are the 16-50 and 50-135 so different in focus response?

Getting frustrated.

10-22-2015, 10:40 AM	#1
7samurai Site Supporter Join Date: Apr 2010 Location: Rancho Cucamonga, CA Photos: Albums Posts: 474	16-50 focus hunting Just bought and returned a 16-50. It was focus hunting even under high contrast subjects. It would refuse to lock focus about 10% of the time. It would also take a number of adjustments before locking focus. (Hunting). Before I order a replacement, I want to verify this is not normal for this lense.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Pentax DA* 16-50 PDAF front focus when stopping down.	Huy	Troubleshooting and Beginner Help	4	03-23-2015 10:09 AM
DA*16-50 focus problem	LB1103	Troubleshooting and Beginner Help	11	08-25-2014 09:24 AM
DA* 16-50 Focus Issue	tigershoot	Pentax SLR Lens Discussion	4	12-05-2009 02:35 PM
My 16-50 focus problems	qksilver	Pentax SLR Lens Discussion	12	03-12-2009 12:16 PM

10-22-2015, 10:58 AM	#2
jatrax Site Supporter Join Date: May 2010 Location: Washington Cascades Photos: Gallery \| Albums Posts: 12,991	Not normal at all. Mine is quite reliable at locking focus, not necessarily the fastest focusing lens I own but it doesn't hunt. However, if the SDM motor is failing it can appear to hunt but what is actually happening is the lens motor is not moving the elements correctly so the focus attempt fails. This should not be happening on a new lens as even those that had problems (prior to 2012) worked fine for a long time before issues arose.

10-22-2015, 11:20 AM	#3
7samurai Site Supporter Join Date: Apr 2010 Location: Rancho Cucamonga, CA Photos: Albums Posts: 474 Original Poster	Thank you for the info. Comparing it against my 16-45, the 16-45 was very reliable and faster at focusing than the 16-50. Every focus attempt on the 16-50 included at least 5-10 adjustment of the motor before it finally aquired focus. This made it impossible to even shoot shots of my slow walking dog. I'll see how the second one goes.

10-22-2015, 11:36 AM	#4
K57XR Veteran Member Join Date: Feb 2011 Location: Colorado, USA Posts: 830	Originally posted by 7samurai Every focus attempt on the 16-50 included at least 5-10 adjustment of the motor before it finally aquired focus. It shouldn't do that on a regular basis. Maybe on challenging scenes? Mine runs on screw-drive and hunts once in a while but we're talking indoor poor lighting or low contrast subjects.

10-22-2015, 12:39 PM	#5
david94903 Loyal Site Supporter Join Date: Nov 2010 Location: San Rafael, CA Photos: Gallery \| Albums Posts: 806	I think you were experiencing the early stages of SDM failure. My 16-50 started focus hunting more and more prior to the SDM failure. Had it repaired through CRIS, and after about six months the focus hunting began again and then a second failure. Have since disabled the SDM, and find that I don't have any focus hunting issues with the screw drive.

10-22-2015, 01:17 PM	#6
7samurai Site Supporter Join Date: Apr 2010 Location: Rancho Cucamonga, CA Photos: Albums Posts: 474 Original Poster	Just ordered another one. The SDM is not inspiring confidence. If I keep the second one, might have to eBay a body to do the screw conversion. Sorry for raising the SDM issue again.

10-24-2015, 01:15 PM	#7
7samurai Site Supporter Join Date: Apr 2010 Location: Rancho Cucamonga, CA Photos: Albums Posts: 474 Original Poster	Just got my 2nd copy and found another issue. The second copy is vastly improved, but when focusing in broad daylight, 50mm, f/2.8, and a black shirt, it will not focus. Tried it 20 times and no luck. Stop down to f/3.2, or shorten to 40mm and it seems to focus more often. I know it's difficult conditions but the 50-135 has no issues and is very snappy. Faster than my screw drives. I'm wondering if I'm hitting the limit of the f/2.8 focus sensor. Are the 16-50 and 50-135 so different in focus response? Getting frustrated.