SMC Pentax DA50mm f 1.8 - Auto focus hunting issue

iamarunr · 10-05-2017, 08:34 AM

Just had my new lens, Pentax SMC DA 50mm f1.8 delivered. I tried it on my K-5 and noticed that the lens is struggling to autofocus and it keeps hunting. Tried in Auto, Av, P and Sv. The manual focus seems to be working.

I tried an 18-135mm WR lens to eliminate that it's not the camera body and I was able to take pictures without autofocus issues. So I am sure the camera body is working.

Any help would be much appreciated. I want to make sure it's faulty before returning.

Claudiu · 10-05-2017, 10:31 AM

Originally posted by iamarunr

Just had my new lens, Pentax SMC DA 50mm f1.8 delivered. I tried it on my K-5 and noticed that the lens is struggling to autofocus and it keeps hunting. Tried in Auto, Av, P and Sv. The manual focus seems to be working.

I tried an 18-135mm WR lens to eliminate that it's not the camera body and I was able to take pictures without autofocus issues. So I am sure the camera body is working.

Any help would be much appreciated. I want to make sure it's faulty before returning.

Try it on the trepied, in good light and in LiveView; if it makes always the same, change it; good luck !

Na Horuk · 10-05-2017, 11:05 AM

can you describe the issue a little more? Is the AF slow, or does it just never lock? Or does it lock focus, but the photo is misfocused?

Originally posted by iamarunr

Tried in Auto, Av, P and Sv. The manual focus seems to be working

This should not matter. Auto doesn't let you choose AF modes, but the others let you choose AF.S, AF.A or AF.C and AF point selection. Either way, this should not be a big effect on locking focus, only on where the camera looks for focus and whether it looks for focus once, or continuously.

The DA 50mm f1.8 is a really fast aperture lens, so it should be able to lock focus even in lower light conditions than the DA 18-135mm. But at wide apertures (low f-number), the Depth of focus will be very shallow, so the tolerance of "correct" focus is much higher. If you misfocus only a little at f1.8, it will be quickly visible.

General recommendations I can give:
a) Update camera firmware to the latest version. This is a good idea any time you are using a newer lens, just in case that lens wasn't included in the firmware. Note this can change some of your settings back to defaults. And you need to use a formatted SD card
b) Do a test with tripod and 2 sec timer, Centre point AF.S in good daylight, pointed at an obvious, contrasty subject.
c) Make sure lens is clean and free of damage, grime. Check the back lens element and camera mount. Check the aperture lever works normally

These might not fix the issue directly, but hopefully they will lead to indicators as to what the problem is.

**Just1MoreDave** · 10-05-2017, 11:17 AM

The 18-135 can focus slightly closer so maybe if you were right at 45cm (kind of 17 and three-quarters in ultraprecise American inches) from the subject to the focal plane, the DA 50 f1.8 would appear to struggle. The 18-135 can focus at 40cm, a couple of inches less. Or you can have trouble close to infinity if the 50mm lens is not quite able to reach infinity. (In that case the lens should be returned.) The only other reason I can think of a normal focusing difference between these two lenses is that the 18-135 is set much wider. If it's at 18mm, just the subject being much smaller could give the AF system enough to lock, while the 50mm doesn't get there. Otherwise, the 50mm is letting in at least three times as much light to the AF sensors, so it ought to work great.

KDD · 10-05-2017, 06:01 PM

Try to RESET your camera body!!!!

iamarunr · 10-05-2017, 10:38 PM

Thanks everyone for your suggestions. I really appreciate it. I tried all the mentioned troubleshooting steps but no joy. I really love the lens though. I tried taking some shots in manual and the pictures are stunningly gorgeous. Can't wait to get the replacement and see how it turns out. Thanks again team! Cheers!

---------- Post added 10-06-17 at 12:38 AM ----------

Originally posted by KDD

Try to RESET your camera body!!!!

Tried this step but no luck.

---------- Post added 10-06-17 at 12:39 AM ----------

Originally posted by Na Horuk

can you describe the issue a little more? Is the AF slow, or does it just never lock? Or does it lock focus, but the photo is misfocused?

This should not matter. Auto doesn't let you choose AF modes, but the others let you choose AF.S, AF.A or AF.C and AF point selection. Either way, this should not be a big effect on locking focus, only on where the camera looks for focus and whether it looks for focus once, or continuously.

The DA 50mm f1.8 is a really fast aperture lens, so it should be able to lock focus even in lower light conditions than the DA 18-135mm. But at wide apertures (low f-number), the Depth of focus will be very shallow, so the tolerance of "correct" focus is much higher. If you misfocus only a little at f1.8, it will be quickly visible.

General recommendations I can give:
a) Update camera firmware to the latest version. This is a good idea any time you are using a newer lens, just in case that lens wasn't included in the firmware. Note this can change some of your settings back to defaults. And you need to use a formatted SD card
b) Do a test with tripod and 2 sec timer, Centre point AF.S in good daylight, pointed at an obvious, contrasty subject.
c) Make sure lens is clean and free of damage, grime. Check the back lens element and camera mount. Check the aperture lever works normally

These might not fix the issue directly, but hopefully they will lead to indicators as to what the problem is.

Great suggestions. Thank you for taking the time to write to me but it didn't work and I am shipping it back. Thanks though.

Na Horuk · 10-06-2017, 03:57 AM

Yeah, sometimes you just get a lens that is not working properly

Hope you get a great copy to enjoy next!

10-05-2017, 08:34 AM	#1
iamarunr Junior Member Join Date: Apr 2011 Location: Nashville Posts: 38	SMC Pentax DA50mm f 1.8 - Auto focus hunting issue Just had my new lens, Pentax SMC DA 50mm f1.8 delivered. I tried it on my K-5 and noticed that the lens is struggling to autofocus and it keeps hunting. Tried in Auto, Av, P and Sv. The manual focus seems to be working. I tried an 18-135mm WR lens to eliminate that it's not the camera body and I was able to take pictures without autofocus issues. So I am sure the camera body is working. Any help would be much appreciated. I want to make sure it's faulty before returning.

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10-05-2017, 10:31 AM	#2
Claudiu Forum Member Join Date: Apr 2015 Location: Normandy Photos: Gallery \| Albums Posts: 59	Originally posted by iamarunr Just had my new lens, Pentax SMC DA 50mm f1.8 delivered. I tried it on my K-5 and noticed that the lens is struggling to autofocus and it keeps hunting. Tried in Auto, Av, P and Sv. The manual focus seems to be working. I tried an 18-135mm WR lens to eliminate that it's not the camera body and I was able to take pictures without autofocus issues. So I am sure the camera body is working. Any help would be much appreciated. I want to make sure it's faulty before returning. Try it on the trepied, in good light and in LiveView; if it makes always the same, change it; good luck !

10-05-2017, 11:05 AM	#3
Na Horuk Veteran Member Join Date: Feb 2012 Location: Slovenia, probably Photos: Gallery \| Albums Posts: 11,186	can you describe the issue a little more? Is the AF slow, or does it just never lock? Or does it lock focus, but the photo is misfocused? Originally posted by iamarunr Tried in Auto, Av, P and Sv. The manual focus seems to be working This should not matter. Auto doesn't let you choose AF modes, but the others let you choose AF.S, AF.A or AF.C and AF point selection. Either way, this should not be a big effect on locking focus, only on where the camera looks for focus and whether it looks for focus once, or continuously. The DA 50mm f1.8 is a really fast aperture lens, so it should be able to lock focus even in lower light conditions than the DA 18-135mm. But at wide apertures (low f-number), the Depth of focus will be very shallow, so the tolerance of "correct" focus is much higher. If you misfocus only a little at f1.8, it will be quickly visible. General recommendations I can give: a) Update camera firmware to the latest version. This is a good idea any time you are using a newer lens, just in case that lens wasn't included in the firmware. Note this can change some of your settings back to defaults. And you need to use a formatted SD card b) Do a test with tripod and 2 sec timer, Centre point AF.S in good daylight, pointed at an obvious, contrasty subject. c) Make sure lens is clean and free of damage, grime. Check the back lens element and camera mount. Check the aperture lever works normally These might not fix the issue directly, but hopefully they will lead to indicators as to what the problem is.

10-05-2017, 11:17 AM	#4
Just1MoreDave Site Supporter Join Date: Feb 2007 Location: Aurora, CO Photos: Gallery \| Albums Posts: 6,340	The 18-135 can focus slightly closer so maybe if you were right at 45cm (kind of 17 and three-quarters in ultraprecise American inches) from the subject to the focal plane, the DA 50 f1.8 would appear to struggle. The 18-135 can focus at 40cm, a couple of inches less. Or you can have trouble close to infinity if the 50mm lens is not quite able to reach infinity. (In that case the lens should be returned.) The only other reason I can think of a normal focusing difference between these two lenses is that the 18-135 is set much wider. If it's at 18mm, just the subject being much smaller could give the AF system enough to lock, while the 50mm doesn't get there. Otherwise, the 50mm is letting in at least three times as much light to the AF sensors, so it ought to work great.

10-05-2017, 06:01 PM	#5
KDD Veteran Member Join Date: Sep 2013 Photos: Gallery \| Albums Posts: 403	Try to RESET your camera body!!!!

10-05-2017, 10:38 PM	#6
iamarunr Junior Member Join Date: Apr 2011 Location: Nashville Posts: 38 Original Poster	Thanks everyone for your suggestions. I really appreciate it. I tried all the mentioned troubleshooting steps but no joy. I really love the lens though. I tried taking some shots in manual and the pictures are stunningly gorgeous. Can't wait to get the replacement and see how it turns out. Thanks again team! Cheers! ---------- Post added 10-06-17 at 12:38 AM ---------- Originally posted by KDD Try to RESET your camera body!!!! Tried this step but no luck. ---------- Post added 10-06-17 at 12:39 AM ---------- Originally posted by Na Horuk can you describe the issue a little more? Is the AF slow, or does it just never lock? Or does it lock focus, but the photo is misfocused? This should not matter. Auto doesn't let you choose AF modes, but the others let you choose AF.S, AF.A or AF.C and AF point selection. Either way, this should not be a big effect on locking focus, only on where the camera looks for focus and whether it looks for focus once, or continuously. The DA 50mm f1.8 is a really fast aperture lens, so it should be able to lock focus even in lower light conditions than the DA 18-135mm. But at wide apertures (low f-number), the Depth of focus will be very shallow, so the tolerance of "correct" focus is much higher. If you misfocus only a little at f1.8, it will be quickly visible. General recommendations I can give: a) Update camera firmware to the latest version. This is a good idea any time you are using a newer lens, just in case that lens wasn't included in the firmware. Note this can change some of your settings back to defaults. And you need to use a formatted SD card b) Do a test with tripod and 2 sec timer, Centre point AF.S in good daylight, pointed at an obvious, contrasty subject. c) Make sure lens is clean and free of damage, grime. Check the back lens element and camera mount. Check the aperture lever works normally These might not fix the issue directly, but hopefully they will lead to indicators as to what the problem is. Great suggestions. Thank you for taking the time to write to me but it didn't work and I am shipping it back. Thanks though.

10-06-2017, 03:57 AM	#7
Na Horuk Veteran Member Join Date: Feb 2012 Location: Slovenia, probably Photos: Gallery \| Albums Posts: 11,186	Yeah, sometimes you just get a lens that is not working properly Hope you get a great copy to enjoy next!