Pentax KM - lens sets itself to smallest aperture

Ray-uk · 04-26-2021, 08:38 AM

Originally posted by raindog

I understand there should be pictures here but for some reason I can't see any...

Well they were there but fell down a black hole somewhere. I have just put them back.

stevebrot · 04-26-2021, 10:40 AM - **1 Like**

Originally posted by UncleVanya

That’s freaky. I assume the aperture on this lens is de-clicked? Maybe the person who said that connected something wrong in the lens?

There is something missing to this story and I think you may have found a clue. Added: I just viewed the video and the cause is obvious. The lens is declicked and as a result the aperture ring provides no resistance to the spring-loaded body side coupling.

Steve

titrisol · 04-26-2021, 10:57 AM

That seems to be more a lens than camera issue
Maybe someone serviced the lens and lost the small ball bearing of the aperture ring so there is no resistance to the body spring loaded aperture ring
PS. Someone called it declicked... why would anyone do that to a lens?

**UncleVanya** · 04-26-2021, 11:08 AM - **1 Like**

Originally posted by titrisol

That seems to be more a lens than camera issue
Maybe someone serviced the lens and lost the small ball bearing of the aperture ring so there is no resistance to the body spring loaded aperture ring
PS. Someone called it declicked... why would anyone do that to a lens?

Video users on a non Pentax platform. It makes changing aperture step less and quiet.

Ray-uk · 04-26-2021, 11:11 AM - **1 Like**

Originally posted by titrisol

PS. Someone called it declicked... why would anyone do that to a lens?

Seems to be a common thing to do if you're using it for video.
I don't do video but the only advantage I can see is that it would allow you to do fade in and fade out shots.

To my mind it is just an easy way to ruin a good lens.

stevebrot · 04-26-2021, 11:59 AM

Originally posted by Ray-uk

Seems to be a common thing to do if you're using it for video.
I don't do video but the only advantage I can see is that it would allow you to do fade in and fade out shots.

I think the technique is called (variously) aperture, iris, or DOF pull. It is used to modify DOF on the fly. Managing exposure can be problematic, but when done well, the effect can be compelling. Aperture pull may also be used to change exposure during a take.

Steve

raindog · 04-26-2021, 01:24 PM

Originally posted by stevebrot

There is something missing to this story and I think you may have found a clue. Added: I just viewed the video and the cause is obvious. The lens is declicked and as a result the aperture ring provides no resistance to the spring-loaded body side coupling.

Steve

That sounds convincing, but wait! It worked alright for years, and just started doing that thing recently. Does your theory still stand?

---------- Post added 04-26-21 at 01:26 PM ----------

Originally posted by raindog

That sounds convincing, but wait! It worked alright for years, and just started doing that thing recently. Does your theory still stand?

Plus, again, it works well when used with an adapter on a Fuji mirrorless. I would expect it to just not stop at power f stops at all...

---------- Post added 04-26-21 at 01:29 PM ----------

Originally posted by Ray-uk

Well they were there but fell down a black hole somewhere. I have just put them back.

Everything shown in the picture applies to the lens. Exactly the same.

stevebrot · 04-26-2021, 04:39 PM - **1 Like**

Originally posted by raindog

That sounds convincing, but wait! It worked alright for years, and just started doing that thing recently. Does your theory still stand?

The proof is in your video. But wait! Do the aperture click stops on the 28mm lens still work or does the ring rotate freely (no clicks) when off camera? Unless a small gremlin lives in lens or camera, what you are seeing is what I would expect from a declicked lens on a standard K-mount body.* If you have lent your lens out in the recent past, you might want to talk to person that borrowed it.

Steve

* A declicked lens works fine on a Pentax dSLR due to those cameras having a non-coupled mount.

raindog · 04-26-2021, 10:18 PM

Originally posted by stevebrot

The proof is in your video. But wait! Do the aperture click stops on the 28mm lens still work or does the ring rotate freely (no clicks) when off camera? Unless a small gremlin lives in lens or camera, what you are seeing is what I would expect from a declicked lens on a standard K-mount body.* If you have lent your lens out in the recent past, you might want to talk to person that borrowed it.

Steve

* A declicked lens works fine on a Pentax dSLR due to those cameras having a non-coupled mount.

Ok, all sounds right, just one mystery left: this is my lens and was never loaned to anyone. It used to be ok. Can a lens declick itself with time?

Ray-uk · 04-27-2021, 02:40 AM

In theory yes, if the lubrication on the spring and ball have dried out then it could become stuck in the inward position.

**UncleVanya** · 04-27-2021, 07:40 PM

Originally posted by raindog

Ok, all sounds right, just one mystery left: this is my lens and was never loaned to anyone. It used to be ok. Can a lens declick itself with time?

Just to confirm:
If you take the lens and mount it somewhere else or even have it in mounted and you turn the aperture does it have distinct discreet steps or does it turn freely without clicks?

raindog · 04-27-2021, 09:23 PM - **1 Like**

Originally posted by UncleVanya

Just to confirm:
If you take the lens and mount it somewhere else or even have it in mounted and you turn the aperture does it have distinct discreet steps or does it turn freely without clicks?

Kind of in between. It is quite smooth but feels like fine grit or teeth. And as I insist on saying: it used to work fine

**UncleVanya** · 04-27-2021, 09:28 PM

Originally posted by raindog

Kind of in between. It is quite smooth but feels like fine grit or teeth. And as I insist on saying: it used to work fine

It does seem like the aperture click lost its mojo. Maybe the ball bearing is stuck as someone mentioned. A CLA might fix this.

04-26-2021, 10:40 AM - 1 Like	#17
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by UncleVanya That’s freaky. I assume the aperture on this lens is de-clicked? Maybe the person who said that connected something wrong in the lens? There is something missing to this story and I think you may have found a clue. Added: I just viewed the video and the cause is obvious. The lens is declicked and as a result the aperture ring provides no resistance to the spring-loaded body side coupling. Steve Last edited by stevebrot; 04-26-2021 at 10:47 AM.

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04-26-2021, 08:38 AM	#16
Ray-uk Senior Member Join Date: Oct 2013 Location: Kent Photos: Gallery Posts: 159	Originally posted by raindog I understand there should be pictures here but for some reason I can't see any... Well they were there but fell down a black hole somewhere. I have just put them back.

04-26-2021, 10:57 AM	#18
titrisol Pentaxian Join Date: Dec 2007 Location: In the most populated state... state of denial Photos: Gallery \| Albums Posts: 1,851	That seems to be more a lens than camera issue Maybe someone serviced the lens and lost the small ball bearing of the aperture ring so there is no resistance to the body spring loaded aperture ring PS. Someone called it declicked... why would anyone do that to a lens?

04-26-2021, 11:08 AM - 1 Like	#19
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,381	Originally posted by titrisol That seems to be more a lens than camera issue Maybe someone serviced the lens and lost the small ball bearing of the aperture ring so there is no resistance to the body spring loaded aperture ring PS. Someone called it declicked... why would anyone do that to a lens? Video users on a non Pentax platform. It makes changing aperture step less and quiet.

04-26-2021, 11:11 AM - 1 Like	#20
Ray-uk Senior Member Join Date: Oct 2013 Location: Kent Photos: Gallery Posts: 159	Originally posted by titrisol PS. Someone called it declicked... why would anyone do that to a lens? Seems to be a common thing to do if you're using it for video. I don't do video but the only advantage I can see is that it would allow you to do fade in and fade out shots. To my mind it is just an easy way to ruin a good lens.

04-26-2021, 11:59 AM	#21
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by Ray-uk Seems to be a common thing to do if you're using it for video. I don't do video but the only advantage I can see is that it would allow you to do fade in and fade out shots. I think the technique is called (variously) aperture, iris, or DOF pull. It is used to modify DOF on the fly. Managing exposure can be problematic, but when done well, the effect can be compelling. Aperture pull may also be used to change exposure during a take. Steve

04-26-2021, 01:24 PM	#22
raindog New Member Join Date: Apr 2021 Posts: 10 Original Poster	Originally posted by stevebrot There is something missing to this story and I think you may have found a clue. Added: I just viewed the video and the cause is obvious. The lens is declicked and as a result the aperture ring provides no resistance to the spring-loaded body side coupling. Steve That sounds convincing, but wait! It worked alright for years, and just started doing that thing recently. Does your theory still stand? ---------- Post added 04-26-21 at 01:26 PM ---------- Originally posted by raindog That sounds convincing, but wait! It worked alright for years, and just started doing that thing recently. Does your theory still stand? Plus, again, it works well when used with an adapter on a Fuji mirrorless. I would expect it to just not stop at power f stops at all... ---------- Post added 04-26-21 at 01:29 PM ---------- Originally posted by Ray-uk Well they were there but fell down a black hole somewhere. I have just put them back. Everything shown in the picture applies to the lens. Exactly the same.

04-26-2021, 04:39 PM - 1 Like	#23
stevebrot Otis Memorial Pentaxian Join Date: Mar 2007 Location: Vancouver (USA) Photos: Gallery \| Albums Posts: 42,007	Originally posted by raindog That sounds convincing, but wait! It worked alright for years, and just started doing that thing recently. Does your theory still stand? The proof is in your video. But wait! Do the aperture click stops on the 28mm lens still work or does the ring rotate freely (no clicks) when off camera? Unless a small gremlin lives in lens or camera, what you are seeing is what I would expect from a declicked lens on a standard K-mount body.* If you have lent your lens out in the recent past, you might want to talk to person that borrowed it. Steve * A declicked lens works fine on a Pentax dSLR due to those cameras having a non-coupled mount.

04-26-2021, 10:18 PM	#24
raindog New Member Join Date: Apr 2021 Posts: 10 Original Poster	Originally posted by stevebrot The proof is in your video. But wait! Do the aperture click stops on the 28mm lens still work or does the ring rotate freely (no clicks) when off camera? Unless a small gremlin lives in lens or camera, what you are seeing is what I would expect from a declicked lens on a standard K-mount body.* If you have lent your lens out in the recent past, you might want to talk to person that borrowed it. Steve * A declicked lens works fine on a Pentax dSLR due to those cameras having a non-coupled mount. Ok, all sounds right, just one mystery left: this is my lens and was never loaned to anyone. It used to be ok. Can a lens declick itself with time?

04-27-2021, 02:40 AM	#25
Ray-uk Senior Member Join Date: Oct 2013 Location: Kent Photos: Gallery Posts: 159	In theory yes, if the lubrication on the spring and ball have dried out then it could become stuck in the inward position.

04-27-2021, 07:40 PM	#26
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,381	Originally posted by raindog Ok, all sounds right, just one mystery left: this is my lens and was never loaned to anyone. It used to be ok. Can a lens declick itself with time? Just to confirm: If you take the lens and mount it somewhere else or even have it in mounted and you turn the aperture does it have distinct discreet steps or does it turn freely without clicks?

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04-27-2021, 09:23 PM - 1 Like	#27
raindog New Member Join Date: Apr 2021 Posts: 10 Original Poster	Originally posted by UncleVanya Just to confirm: If you take the lens and mount it somewhere else or even have it in mounted and you turn the aperture does it have distinct discreet steps or does it turn freely without clicks? Kind of in between. It is quite smooth but feels like fine grit or teeth. And as I insist on saying: it used to work fine

04-27-2021, 09:28 PM	#28
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,381	Originally posted by raindog Kind of in between. It is quite smooth but feels like fine grit or teeth. And as I insist on saying: it used to work fine It does seem like the aperture click lost its mojo. Maybe the ball bearing is stuck as someone mentioned. A CLA might fix this.