DA* 16-50mm aperture lever jamming when bayonet mount screwed down

Penta · 11-14-2020, 09:42 AM

I recently got a used faulty DA* 16-50mm lens off someone under the impression that only the AF was non functioning ie. manual focus only. However after inspecting the lens I noticed the aperture lever would get stuck in different positions, so took it apart and after further examination, suspected the aperture spring was past its best so have just replaced that but the problem's still there.

The main problem is with the bayonet mount removed the aperture/lever works and returns fine but as soon as I've screwed down the bayonet fitting it causes the aperture lever to get stuck again. When the bayonet is fully screwed in place it's like it causes resistance to the aperture lever and so the lever will just get stuck in different positions.

Has anyone come across this before ? I think I probably need to raise the bayonet fitting very slightly by adding little washers on the 5 bayonet screw holes or something like this so the bayonet doesn't clamp down so hard on the aperture ring. Just a bit confused why I would have to do this in the first place!

Any suggestions welcome, cheers

JohnX · 11-14-2020, 10:06 AM - **1 Like**

Distortion in the bayonet mount? Aperture lever bent?

35mmfilmfan · 11-14-2020, 10:07 AM - **1 Like**

Is it possible that the aperture lever is bent slightly, and is binding on the mount ? Wouldn't moving the mount affect focusing ?

@JohnX Beat me to it !

Doug James · 11-14-2020, 10:11 AM - **1 Like**

Could you have over tighten the screws?

maw · 11-14-2020, 10:29 AM - **1 Like**

Hi Penta,

At a remote it is difficult to understand what is really the cause of the malfunction, I looked for the mechanical scheme but I do not know if it exists.

I found these instructions with illustrations for SDM repair, that may help you. Pentax 16-50 mm SDM (DA*)

and this discussion on the forum Pentax SDM issues (like everyone else)

I hope you will be able to repair it promptly.

Mario

Penta · 11-14-2020, 10:31 AM

Thanks all I had a look at the aperture lever and thought it looked like there was enough play on either side but will look again as that would make the most sense.

Yes there may also be some distortion in the mount although maybe only minor as it's definitely not noticeable. Will have another look at it and report back.

---------- Post added 11-14-20 at 05:35 PM ----------

Originally posted by maw

Hi Penta,

At a remote it is difficult to understand what is really the cause of the malfunction, I looked for the mechanical scheme but I do not know if it exists.

I found these instructions with illustrations for SDM repair, that may help you. Pentax 16-50 mm SDM (DA*)

I hope you will be able to repair it promptly.

Mario

That's really useful Mario as I hadn't found that one before. thank you.

stevebrot · 11-14-2020, 11:03 AM - **1 Like**

Originally posted by Penta

Any suggestions welcome, cheers

Sell it on eBay for parts? Repurpose as a vase?

Steve

Penta · 11-14-2020, 11:14 AM

Haha @stevebrot not a bad idea!

I've just mounted it on a K30 with some of the screws not fully tight to allow the lever to move freely and in AV mode it stops between f5.6 - f32, not possible to go lower.... wait the lens is only mean't to go to f22 isn't it?! Calibration fault issue there ?

Another curious thing is the camera doesn't recognise the lens and asks to input focal length each time it's mounted... is that normal with the 16-50mm ?

stevebrot · 11-14-2020, 11:37 AM - **1 Like**

Originally posted by Penta

Another curious thing is the camera doesn't recognise the lens and asks to input focal length each time it's mounted... is that normal with the 16-50mm ?

Ummmm...no...

Steve

maw · 11-14-2020, 11:52 AM - **1 Like**

Originally posted by Penta

is that normal with the 16-50mm ?

It is normal in the abnormality of things, it is assumed that after the design and before being put on the market,
those unfortunate optics with that type of SDM engine have always had various types of failures.

Take a look: Pentax Lens Disassembly Database

Also in China also complain about these problems: SDM DA 16-50mm

Mario

Penta · 11-14-2020, 11:59 AM

I'm starting to feel like this particular lenses problems are slowly unraveling to be an almighty can of worms.... dooh

pschlute · 11-14-2020, 12:00 PM - **1 Like**

Originally posted by Penta

I've just mounted it on a K30 with some of the screws not fully tight to allow the lever to move freely and in AV mode it stops between f5.6 - f32, not possible to go lower.... wait the lens is only mean't to go to f22 isn't it?! Calibration fault issue there ?

The lens has a range of 2.8-22. Are you getting exposure problems because the camera is misreading the aperture ?

Originally posted by Penta

Another curious thing is the camera doesn't recognise the lens and asks to input focal length each time it's mounted... is that normal with the 16-50mm ?

No that is not normal. Sounds like you have quite a few issues here.

If the exposure is correct but the reading is wrong, then maybe you have a decent lens for what I expect was a cheap price. What is the lens performance like ?

HarisF1 · 11-14-2020, 12:43 PM - **1 Like**

Putting washers on will affect infinity focus.

Also the aperture value issue suggests there may be some dodgy contacts - make sure all pins are seated perfectly.

Penta · 11-14-2020, 12:57 PM

Originally posted by pschlute

The lens has a range of 2.8-22. Are you getting exposure problems because the camera is misreading the aperture ?

No that is not normal. Sounds like you have quite a few issues here.

If the exposure is correct but the reading is wrong, then maybe you have a decent lens for what I expect was a cheap price. What is the lens performance like ?

Exposure seems ok even though the aperture is funky, ok image wise with manual focus although I've never tried the 16-50 before so nothing to compare to. Tbh it's not really usable in the current state...

---------- Post added 11-14-20 at 08:01 PM ----------

Originally posted by HarisF1

Putting washers on will affect infinity focus.

Also the aperture value issue suggests there may be some dodgy contacts - make sure all pins are seated perfectly.

Yes there must be another issue related to the electronics which would explain why its not getting the focal reading to the camera. All contacts have been reseated a number of times and it arrived with these faults before I started to investigate. I think the aperture problem is also related to the lever mechanism.

**Belnan** · 11-14-2020, 01:04 PM

Seems like something is not going back together correctly. Have you tried again?

11-14-2020, 09:42 AM	#1
Penta Junior Member Join Date: Jan 2013 Posts: 42	*DA 16-50mm aperture lever jamming when bayonet mount screwed down** I recently got a used faulty DA* 16-50mm lens off someone under the impression that only the AF was non functioning ie. manual focus only. However after inspecting the lens I noticed the aperture lever would get stuck in different positions, so took it apart and after further examination, suspected the aperture spring was past its best so have just replaced that but the problem's still there. The main problem is with the bayonet mount removed the aperture/lever works and returns fine but as soon as I've screwed down the bayonet fitting it causes the aperture lever to get stuck again. When the bayonet is fully screwed in place it's like it causes resistance to the aperture lever and so the lever will just get stuck in different positions. Has anyone come across this before ? I think I probably need to raise the bayonet fitting very slightly by adding little washers on the 5 bayonet screw holes or something like this so the bayonet doesn't clamp down so hard on the aperture ring. Just a bit confused why I would have to do this in the first place! Any suggestions welcome, cheers

11-14-2020, 10:29 AM - 1 Like	#5
maw Pentaxian Join Date: Feb 2014 Location: Sassari (Italy) Posts: 1,118	Hi Penta, At a remote it is difficult to understand what is really the cause of the malfunction, I looked for the mechanical scheme but I do not know if it exists. I found these instructions with illustrations for SDM repair, that may help you. *Pentax 16-50 mm SDM (DA) and this discussion on the forum Pentax SDM issues (like everyone else)** I hope you will be able to repair it promptly. Mario Last edited by maw; 11-14-2020 at 10:47 AM.

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11-14-2020, 10:06 AM - 1 Like	#2
JohnX Pentaxian Join Date: Jul 2009 Location: London Posts: 1,116	Distortion in the bayonet mount? Aperture lever bent?

11-14-2020, 10:07 AM - 1 Like	#3
35mmfilmfan Pentaxian Join Date: Oct 2016 Location: Norfolk, UK Posts: 4,329	Is it possible that the aperture lever is bent slightly, and is binding on the mount ? Wouldn't moving the mount affect focusing ? @JohnX Beat me to it !

11-14-2020, 10:11 AM - 1 Like	#4
Doug James Junior Member Join Date: Sep 2017 Location: Manitoba Posts: 49	Could you have over tighten the screws?

11-14-2020, 10:31 AM	#6
Penta Junior Member Join Date: Jan 2013 Posts: 42 Original Poster	Thanks all I had a look at the aperture lever and thought it looked like there was enough play on either side but will look again as that would make the most sense. Yes there may also be some distortion in the mount although maybe only minor as it's definitely not noticeable. Will have another look at it and report back. ---------- Post added 11-14-20 at 05:35 PM ---------- Originally posted by maw Hi Penta, At a remote it is difficult to understand what is really the cause of the malfunction, I looked for the mechanical scheme but I do not know if it exists. I found these instructions with illustrations for SDM repair, that may help you. *Pentax 16-50 mm SDM (DA)** I hope you will be able to repair it promptly. Mario That's really useful Mario as I hadn't found that one before. thank you.

11-14-2020, 11:03 AM - 1 Like	#7
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by Penta Any suggestions welcome, cheers Sell it on eBay for parts? Repurpose as a vase? Steve

11-14-2020, 11:14 AM	#8
Penta Junior Member Join Date: Jan 2013 Posts: 42 Original Poster	Haha @stevebrot not a bad idea! I've just mounted it on a K30 with some of the screws not fully tight to allow the lever to move freely and in AV mode it stops between f5.6 - f32, not possible to go lower.... wait the lens is only mean't to go to f22 isn't it?! Calibration fault issue there ? Another curious thing is the camera doesn't recognise the lens and asks to input focal length each time it's mounted... is that normal with the 16-50mm ?

11-14-2020, 11:37 AM - 1 Like	#9
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by Penta Another curious thing is the camera doesn't recognise the lens and asks to input focal length each time it's mounted... is that normal with the 16-50mm ? Ummmm...no... Steve

11-14-2020, 11:52 AM - 1 Like	#10
maw Pentaxian Join Date: Feb 2014 Location: Sassari (Italy) Posts: 1,118	Originally posted by Penta is that normal with the 16-50mm ? It is normal in the abnormality of things, it is assumed that after the design and before being put on the market, those unfortunate optics with that type of SDM engine have always had various types of failures. Take a look: Pentax Lens Disassembly Database Also in China also complain about these problems: SDM DA 16-50mm Mario

11-14-2020, 11:59 AM	#11
Penta Junior Member Join Date: Jan 2013 Posts: 42 Original Poster	I'm starting to feel like this particular lenses problems are slowly unraveling to be an almighty can of worms.... dooh

11-14-2020, 12:00 PM - 1 Like	#12
pschlute Moderator Loyal Site Supporter Join Date: Mar 2007 Location: Surrey, UK Photos: Gallery Posts: 8,198	Originally posted by Penta I've just mounted it on a K30 with some of the screws not fully tight to allow the lever to move freely and in AV mode it stops between f5.6 - f32, not possible to go lower.... wait the lens is only mean't to go to f22 isn't it?! Calibration fault issue there ? The lens has a range of 2.8-22. Are you getting exposure problems because the camera is misreading the aperture ? Originally posted by Penta Another curious thing is the camera doesn't recognise the lens and asks to input focal length each time it's mounted... is that normal with the 16-50mm ? No that is not normal. Sounds like you have quite a few issues here. If the exposure is correct but the reading is wrong, then maybe you have a decent lens for what I expect was a cheap price. What is the lens performance like ?

11-14-2020, 12:43 PM - 1 Like	#13
HarisF1 Veteran Member Join Date: Apr 2016 Posts: 543	Putting washers on will affect infinity focus. Also the aperture value issue suggests there may be some dodgy contacts - make sure all pins are seated perfectly.

11-14-2020, 12:57 PM	#14
Penta Junior Member Join Date: Jan 2013 Posts: 42 Original Poster	Originally posted by pschlute The lens has a range of 2.8-22. Are you getting exposure problems because the camera is misreading the aperture ? No that is not normal. Sounds like you have quite a few issues here. If the exposure is correct but the reading is wrong, then maybe you have a decent lens for what I expect was a cheap price. What is the lens performance like ? Exposure seems ok even though the aperture is funky, ok image wise with manual focus although I've never tried the 16-50 before so nothing to compare to. Tbh it's not really usable in the current state... ---------- Post added 11-14-20 at 08:01 PM ---------- Originally posted by HarisF1 Putting washers on will affect infinity focus. Also the aperture value issue suggests there may be some dodgy contacts - make sure all pins are seated perfectly. Yes there must be another issue related to the electronics which would explain why its not getting the focal reading to the camera. All contacts have been reseated a number of times and it arrived with these faults before I started to investigate. I think the aperture problem is also related to the lever mechanism.

11-14-2020, 01:04 PM	#15
Belnan Site Supporter Join Date: Jul 2010 Location: Nova Scotia Photos: Albums Posts: 1,090	Seems like something is not going back together correctly. Have you tried again?