SMC Pentax-F 1:4.5-5.6 35-80mm lens works.. occasionally?

AnttiV · 09-26-2016, 09:53 PM

Hi. First off, I'm thrilled to finally have my own Pentax camera (been lurking here for ages), even if it is an older one (K-m). But now that I have it I can finally use my other PK-lenses (that I've used adapted with my DMC-G3) on a "real" Pentax body and use some of the features some of them have that are not available adapted. Like the Aperture and Focus on F lenses.

However I bumped into a really odd problem with this one. It works, occasionally, when zoomed to 35mm when the camera is first turned on, but if I zoom to 50mm and/or try to quickly focus from far to close, it goes back to MF (instead of AF-S to which I have it set). Then occasionally zooming back to 35mm makes it work again, occasionally squeezing the Aperture ring helps.

This is not a very good or expensive lens, so there isn't probably any point to get it fixed in any shop (the repair probably costs multiple times the cost of the lens), but do any of you know if there's anything "user-fixable" inside? Because to me that sounds terribly familiar having been around electronics my whole life. I could almost bet something that there's a wire loose (or a cold solder) somewhere in the lens. But as I've never even opened an AF lens, I have no idea what to look for. (I've opened a couple MF lenses so I know what to look for in how to open it, but no idea about anything electronic inside a lens).

Should I just suck it up and toss the lens (I do have a 18-55 and a 50-200, so I wouldn't "lose" any focal lengths, but 35-80 is a nice walk-around and a compromise between the two other lenses)?

**paulh** · 09-26-2016, 10:00 PM

Try cleaning the contacts with a small bit of alcohol. That's fixed a few oddball AF problems for me in the past. If it is broken, it's really not worth repairing unless you want to try it yourself for fun or practice

. There are tons of them on the 'bay for around 20 bucks.

AnttiV · 09-27-2016, 01:34 AM

Originally posted by paulh

Try cleaning the contacts with a small bit of alcohol. That's fixed a few oddball AF problems for me in the past. If it is broken, it's really not worth repairing unless you want to try it yourself for fun or practice

. There are tons of them on the 'bay for around 20 bucks.

Unfortunately that didn't help, but thanks for the suggestion. If I shake the camera gently (when lens is attached and the camera is on), it usually goes between AF-S and MF. So there's something loose inside the lens very probably at least. I think I'll scrap that since it is such a cheap lens. Maybe I'll try to ask around locally if anyone wants it free before, but.

Anyways, thanks.

pathdoc · 09-27-2016, 03:34 AM

Well, if it's that much of a dead loss there's nothing to be lost by tearing it down and having a look inside...

AnttiV · 09-27-2016, 03:43 AM

Originally posted by pathdoc

Well, if it's that much of a dead loss there's nothing to be lost by tearing it down and having a look inside...

You have a point there

09-26-2016, 09:53 PM	#1
AnttiV Junior Member Join Date: Jun 2012 Posts: 34	SMC Pentax-F 1:4.5-5.6 35-80mm lens works.. occasionally? Hi. First off, I'm thrilled to finally have my own Pentax camera (been lurking here for ages), even if it is an older one (K-m). But now that I have it I can finally use my other PK-lenses (that I've used adapted with my DMC-G3) on a "real" Pentax body and use some of the features some of them have that are not available adapted. Like the Aperture and Focus on F lenses. However I bumped into a really odd problem with this one. It works, occasionally, when zoomed to 35mm when the camera is first turned on, but if I zoom to 50mm and/or try to quickly focus from far to close, it goes back to MF (instead of AF-S to which I have it set). Then occasionally zooming back to 35mm makes it work again, occasionally squeezing the Aperture ring helps. This is not a very good or expensive lens, so there isn't probably any point to get it fixed in any shop (the repair probably costs multiple times the cost of the lens), but do any of you know if there's anything "user-fixable" inside? Because to me that sounds terribly familiar having been around electronics my whole life. I could almost bet something that there's a wire loose (or a cold solder) somewhere in the lens. But as I've never even opened an AF lens, I have no idea what to look for. (I've opened a couple MF lenses so I know what to look for in how to open it, but no idea about anything electronic inside a lens). Should I just suck it up and toss the lens (I do have a 18-55 and a 50-200, so I wouldn't "lose" any focal lengths, but 35-80 is a nice walk-around and a compromise between the two other lenses)?

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09-26-2016, 10:00 PM	#2
paulh Site Supporter Join Date: Sep 2010 Location: DFW Texas/Ventura County, CA Photos: Gallery \| Albums Posts: 33,301	Try cleaning the contacts with a small bit of alcohol. That's fixed a few oddball AF problems for me in the past. If it is broken, it's really not worth repairing unless you want to try it yourself for fun or practice . There are tons of them on the 'bay for around 20 bucks.

09-27-2016, 01:34 AM	#3
AnttiV Junior Member Join Date: Jun 2012 Posts: 34 Original Poster	Originally posted by paulh Try cleaning the contacts with a small bit of alcohol. That's fixed a few oddball AF problems for me in the past. If it is broken, it's really not worth repairing unless you want to try it yourself for fun or practice . There are tons of them on the 'bay for around 20 bucks. Unfortunately that didn't help, but thanks for the suggestion. If I shake the camera gently (when lens is attached and the camera is on), it usually goes between AF-S and MF. So there's something loose inside the lens very probably at least. I think I'll scrap that since it is such a cheap lens. Maybe I'll try to ask around locally if anyone wants it free before, but. Anyways, thanks.

09-27-2016, 03:34 AM	#4
pathdoc Pentaxian Join Date: Mar 2015 Photos: Gallery \| Albums Posts: 6,381	Well, if it's that much of a dead loss there's nothing to be lost by tearing it down and having a look inside...

09-27-2016, 03:43 AM	#5
AnttiV Junior Member Join Date: Jun 2012 Posts: 34 Original Poster	Originally posted by pathdoc Well, if it's that much of a dead loss there's nothing to be lost by tearing it down and having a look inside... You have a point there