Found the problem with M lenses on my k100!

jboyde · 04-23-2009, 02:46 PM

I noticed the problem when I put my old M lens on the 100d a few months ago. It stayed wide open no matter what. I've had many helpful people troubleshoot the problem but today, after 3 months, I figured it out.

If you look at the picture you'll see that there's a small black metallic tab on the left side of the lens mount. I figure that this is what moves the blades open and closed since its right by where the lever of a lens would go once you mount it.

What happened tho is that the tab was stuck halfway, leaving the lens open. I was able to "un-stick" it and now the tab stays in that top position the way you see it in the picture. Now when I use the aperture ring I can see the image in the viewfinder lighten or darken depending on the f/stop and it meters correctly. When I turn the ring I can see the blades open and close. Before, it would just stay wide open. The tab also springs back to top if you move it down to that halfway position I found it stuck in. Looks like all is well, right?

But guess what, now the blades stay closed when I put on an A lens or later and have them in A mode. When I look thru the viewfinder while any lens is in A the image is completely dark, like f22. And it meters like its f22 no mater what aperture I dial into the camera. Unless, I use the ring. Ironic, huh?

So, it looks like I traded one problem with another. Ugh. My k200d doesn't have this problem so I'm pretty much sure its a body issue with he 100d.

Looks like I'm going to need it serviced.

Last edited by jboyde; 12-10-2010 at 10:56 PM.

SOldBear · 04-23-2009, 03:07 PM

I don't have my K10D body with me here, so I'm writing this based on my memory (many times failing according to my wife

):

The normal location for the tab is at the middle (the "stuck halfway" location in your post). This will keep the M lens at full aperture ("stayed wide open no matter what" in your post) so you can focus easily.

When you hit the shutter release, that tab moves to the top position, closing down the lens's aperture, then after the shutter has closed, moves back to the halfway location (this assumes you have the camera in M mode, the only mode M lens works correctly).

Pentax DSLRs do not allows full-aperture metering with M-lenses. So to meter, you have to hit the green button (K10D, K20D) or the AE-L button (K100D, K110D) with the camera in M mode.

Read this thread.

I don't know what you did to "un-stick" it, but you shouldn't have done that.

See if this thread helps you to bring it back to the "stuck halfway" location.

jboyde · 04-23-2009, 04:40 PM

Fortunately, it snapped back to middle so theres no damage done.
The thing is, it was the only way to use an M lens. Once I put it back to the middle, I'm back in the same position, pardon the pun.

I took a look at the links you posted. Yup, its definitely the actuator spring. When I used the optical preview to see if the tab would move, it didnt. But the way it seems right now, this has been a chronic problem with my k100. The optical preview worked until about 2 months after I bought it. I sorta put it out of my mind since I was using DA lenses more and switched to digital preview. When I used my M lens on it is when this problem became apparent. The actuator isnt controlling the aperture blades as it should. I shoulda noticed that when the optical preview stopped working since it needs to set the lens at the proper f/stop to see the DOF effect. I saw in your dpreview.com post that you too were having the same problem.

I DO see a spring above the tab when I bring it to middle and snap it there, but theres no spring visible below the tab when I move it up. Is there supposed to be one?

Thanks.

SOldBear · 04-23-2009, 06:21 PM

Reset, reset.....

My descriptions are for the K10D. The K100D may be different. I don't know.

I'm not clear about the problem you have with M lens.

Now please try this:

- Set the K100D to M mode.
- Attach an M lens. Set the aperture ring to, say f/16.
- Look through the viewfinder. Hit AE-L. Do you notice the viewfinder getting darker? What's the shutter speed?
- Change the lens's aperture ring setting to f/5.6.
- Hit AE-L. What's the shutter speed?

Please report back.

jboyde · 04-23-2009, 06:53 PM

Originally posted by SOldBear

Reset, reset.....

My descriptions are for the K10D. The K100D may be different. I don't know.

I'm not clear about the problem you have with M lens.

Now please try this:

- Set the K100D to M mode.
- Attach an M lens. Set the aperture ring to, say f/16.
- Look through the viewfinder. Hit AE-L. Do you notice the viewfinder getting darker? What's the shutter speed?
- Change the lens's aperture ring setting to f/5.6.
- Hit AE-L. What's the shutter speed?

Please report back.

Thanks Soldbear.
The viewfinder doesnt get dark at any of the high f/stops. I get that "whish-whish" sound when I push AE-L but theres no change.

I'm pointing my camera at the monitor and here are the numbers:
ISO200 at f/16
shutter speed 1/250

but at f/2.8 at ISO 200
shutter speed 1/250

theres no difference.

Andi Lo · 04-23-2009, 07:16 PM

Originally posted by jboyde

Thanks Soldbear.
The viewfinder doesnt get dark at any of the high f/stops. I get that "whish-whish" sound when I push AE-L but theres no change.

I'm pointing my camera at the monitor and here are the numbers:
ISO200 at f/16
shutter speed 1/250

but at f/2.8 at ISO 200
shutter speed 1/250

theres no difference.

hi jboyde.

Just to clarify, the viewfinder should get dark only during the "whish whish" sound. I don't know what the solution to your problem is unfortunately... just trying to help

jboyde · 04-23-2009, 07:19 PM

Originally posted by Andi Lo

hi jboyde.

Just to clarify, the viewfinder should get dark only during the "whish whish" sound. I don't know what the solution to your problem is unfortunately... just trying to help

I know, and its not doing that.

SOldBear · 04-23-2009, 08:14 PM

jboyde,

Yup. I think you're right. Your K100D is really sick.

jboyde · 04-23-2009, 09:16 PM

Originally posted by SOldBear

jboyde,

Yup. I think you're right. Your K100D is really sick.

Yeahhhh. Sigh. Its ok. I'm glad I live in NYC since its so easy to have it serviced. Good thing its something thats not a hassle to fix and that I use the 100D as my second body.

Thanks for your help.

res3567 · 04-23-2009, 10:19 PM

Originally posted by jboyde

Yeahhhh. Sigh. Its ok. I'm glad I live in NYC since its so easy to have it serviced. Good thing its something thats not a hassle to fix and that I use the 100D as my second body.

Thanks for your help.

Check this out.

Just bought a lens from a guy on EBAY

A Vivitar 100-300 f/5

Mounted it and played with it.

Everytime I use the "Green button" (the equivalant of yor AE button on your K100D) the viewfinder would get dark.

Took off the lens and turned the apeture ring,and the blades did not open up.

The auto aperture works just great.

If I use the M mode and green button, I have permanant f/22

If I use one of the AE modes, I have permanant f/5.

The "Tab" will move the auto aperture lever after the camera exposes wide open in AE mode.

The aperture ring has somehow detached itself from the blades.

Has anyone had this problem with an old lens, and can this be fixed by a pro who specializes in old lenses at reasonable prices?

jboyde · 04-23-2009, 11:01 PM

Originally posted by res3567

Check this out.

Just bought a lens from a guy on EBAY

A Vivitar 100-300 f/5

Mounted it and played with it.

Everytime I use the "Green button" (the equivalant of yor AE button on your K100D) the viewfinder would get dark.

Took off the lens and turned the apeture ring,and the blades did not open up.

The auto aperture works just great.

If I use the M mode and green button, I have permanant f/22

If I use one of the AE modes, I have permanant f/5.

The "Tab" will move the auto aperture lever after the camera exposes wide open in AE mode.

The aperture ring has somehow detached itself from the blades.

Has anyone had this problem with an old lens, and can this be fixed by a pro who specializes in old lenses at reasonable prices?

Is it only with that lens?

I wonder if older lenses affect the newer Pentax DSLRs because their "heavier" than newer ones. New cameras mainly use autoexposure so the blades and the levers arent manipulated as often, so the camera mechanics may be more delicate. Kinda like putting a new Toyota engine in a '74 Chevy Nova. Sure the engine is good for a car thats made out of fiberglass and aluminum but it doesnt have the torque for 2 tons of Detrot steel!

Bad analogy?

res3567 · 04-23-2009, 11:11 PM

Originally posted by jboyde

Is it only with that lens?

I wonder if older lenses affect the newer Pentax DSLRs because their "heavier" than newer ones. New cameras mainly use autoexposure so the blades and the levers arent manipulated as often, so the camera mechanics may be more delicate. Kinda like putting a new Toyota engine in a '74 Chevy Nova. Sure the engine is good for a car thats made out of fiberglass and aluminum but it doesnt have the torque for 2 tons of Detrot steel!

Bad analogy?

Good Point! Well taken!

This is a HEAVY lens.

Another option to investigate.

Havn't had time to FULLY explore all options.

Thank You!

SOldBear · 04-24-2009, 11:50 AM

Originally posted by res3567

The aperture ring has somehow detached itself from the blades.

Has anyone had this problem with an old lens, and can this be fixed by a pro who specializes in old lenses at reasonable prices?

I had a Pentax SMC-M 100mm 1:2.8 with the same symptom.

Technically, it's simple to fix.

The problem with the lens I had was that the lever connecting the aperture ring and the aperture had been broken at the joint. I could not find the replacement part. So I used the lens as an organ donnor for other lenses.

So whether it can be fix depends on what's broken. If something just comes loose, it's easy. If a part is broken, it's not easy.

04-23-2009, 02:46 PM	#1
jboyde Veteran Member Join Date: Apr 2009 Location: New York Posts: 328	Found the problem with M lenses on my k100! I noticed the problem when I put my old M lens on the 100d a few months ago. It stayed wide open no matter what. I've had many helpful people troubleshoot the problem but today, after 3 months, I figured it out. If you look at the picture you'll see that there's a small black metallic tab on the left side of the lens mount. I figure that this is what moves the blades open and closed since its right by where the lever of a lens would go once you mount it. What happened tho is that the tab was stuck halfway, leaving the lens open. I was able to "un-stick" it and now the tab stays in that top position the way you see it in the picture. Now when I use the aperture ring I can see the image in the viewfinder lighten or darken depending on the f/stop and it meters correctly. When I turn the ring I can see the blades open and close. Before, it would just stay wide open. The tab also springs back to top if you move it down to that halfway position I found it stuck in. Looks like all is well, right? But guess what, now the blades stay closed when I put on an A lens or later and have them in A mode. When I look thru the viewfinder while any lens is in A the image is completely dark, like f22. And it meters like its f22 no mater what aperture I dial into the camera. Unless, I use the ring. Ironic, huh? So, it looks like I traded one problem with another. Ugh. My k200d doesn't have this problem so I'm pretty much sure its a body issue with he 100d. Looks like I'm going to need it serviced. Last edited by jboyde; 12-10-2010 at 10:56 PM.

04-23-2009, 03:07 PM	#2
SOldBear Veteran Member Join Date: Feb 2009 Location: Alameda, CA Posts: 3,206	I don't have my K10D body with me here, so I'm writing this based on my memory (many times failing according to my wife ): The normal location for the tab is at the middle (the "stuck halfway" location in your post). This will keep the M lens at full aperture ("stayed wide open no matter what" in your post) so you can focus easily. When you hit the shutter release, that tab moves to the top position, closing down the lens's aperture, then after the shutter has closed, moves back to the halfway location (this assumes you have the camera in M mode, the only mode M lens works correctly). Pentax DSLRs do not allows full-aperture metering with M-lenses. So to meter, you have to hit the green button (K10D, K20D) or the AE-L button (K100D, K110D) with the camera in M mode. Read this thread. I don't know what you did to "un-stick" it, but you shouldn't have done that. See if this thread helps you to bring it back to the "stuck halfway" location. Last edited by SOldBear; 04-23-2009 at 03:13 PM.

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04-23-2009, 04:40 PM	#3
jboyde Veteran Member Join Date: Apr 2009 Location: New York Posts: 328 Original Poster	Fortunately, it snapped back to middle so theres no damage done. The thing is, it was the only way to use an M lens. Once I put it back to the middle, I'm back in the same position, pardon the pun. I took a look at the links you posted. Yup, its definitely the actuator spring. When I used the optical preview to see if the tab would move, it didnt. But the way it seems right now, this has been a chronic problem with my k100. The optical preview worked until about 2 months after I bought it. I sorta put it out of my mind since I was using DA lenses more and switched to digital preview. When I used my M lens on it is when this problem became apparent. The actuator isnt controlling the aperture blades as it should. I shoulda noticed that when the optical preview stopped working since it needs to set the lens at the proper f/stop to see the DOF effect. I saw in your dpreview.com post that you too were having the same problem. I DO see a spring above the tab when I bring it to middle and snap it there, but theres no spring visible below the tab when I move it up. Is there supposed to be one? Thanks.

04-23-2009, 06:21 PM	#4
SOldBear Veteran Member Join Date: Feb 2009 Location: Alameda, CA Posts: 3,206	Reset, reset..... My descriptions are for the K10D. The K100D may be different. I don't know. I'm not clear about the problem you have with M lens. Now please try this: - Set the K100D to M mode. - Attach an M lens. Set the aperture ring to, say f/16. - Look through the viewfinder. Hit AE-L. Do you notice the viewfinder getting darker? What's the shutter speed? - Change the lens's aperture ring setting to f/5.6. - Hit AE-L. What's the shutter speed? Please report back.

04-23-2009, 06:53 PM	#5
jboyde Veteran Member Join Date: Apr 2009 Location: New York Posts: 328 Original Poster	Originally posted by SOldBear Reset, reset..... My descriptions are for the K10D. The K100D may be different. I don't know. I'm not clear about the problem you have with M lens. Now please try this: - Set the K100D to M mode. - Attach an M lens. Set the aperture ring to, say f/16. - Look through the viewfinder. Hit AE-L. Do you notice the viewfinder getting darker? What's the shutter speed? - Change the lens's aperture ring setting to f/5.6. - Hit AE-L. What's the shutter speed? Please report back. Thanks Soldbear. The viewfinder doesnt get dark at any of the high f/stops. I get that "whish-whish" sound when I push AE-L but theres no change. I'm pointing my camera at the monitor and here are the numbers: ISO200 at f/16 shutter speed 1/250 but at f/2.8 at ISO 200 shutter speed 1/250 theres no difference.

04-23-2009, 07:16 PM	#6
Andi Lo Veteran Member Join Date: Jul 2008 Location: Halifax, Nova Scotia Posts: 2,924	Originally posted by jboyde Thanks Soldbear. The viewfinder doesnt get dark at any of the high f/stops. I get that "whish-whish" sound when I push AE-L but theres no change. I'm pointing my camera at the monitor and here are the numbers: ISO200 at f/16 shutter speed 1/250 but at f/2.8 at ISO 200 shutter speed 1/250 theres no difference. hi jboyde. Just to clarify, the viewfinder should get dark only during the "whish whish" sound. I don't know what the solution to your problem is unfortunately... just trying to help

04-23-2009, 07:19 PM	#7
jboyde Veteran Member Join Date: Apr 2009 Location: New York Posts: 328 Original Poster	Originally posted by Andi Lo hi jboyde. Just to clarify, the viewfinder should get dark only during the "whish whish" sound. I don't know what the solution to your problem is unfortunately... just trying to help I know, and its not doing that.

04-23-2009, 08:14 PM	#8
SOldBear Veteran Member Join Date: Feb 2009 Location: Alameda, CA Posts: 3,206	jboyde, Yup. I think you're right. Your K100D is really sick.

04-23-2009, 09:16 PM	#9
jboyde Veteran Member Join Date: Apr 2009 Location: New York Posts: 328 Original Poster	Originally posted by SOldBear jboyde, Yup. I think you're right. Your K100D is really sick. Yeahhhh. Sigh. Its ok. I'm glad I live in NYC since its so easy to have it serviced. Good thing its something thats not a hassle to fix and that I use the 100D as my second body. Thanks for your help.

04-23-2009, 10:19 PM	#10
res3567 Veteran Member Join Date: Sep 2008 Location: Houston Tx. Photos: Gallery Posts: 1,876	Originally posted by jboyde Yeahhhh. Sigh. Its ok. I'm glad I live in NYC since its so easy to have it serviced. Good thing its something thats not a hassle to fix and that I use the 100D as my second body. Thanks for your help. Check this out. Just bought a lens from a guy on EBAY A Vivitar 100-300 f/5 Mounted it and played with it. Everytime I use the "Green button" (the equivalant of yor AE button on your K100D) the viewfinder would get dark. Took off the lens and turned the apeture ring,and the blades did not open up. The auto aperture works just great. If I use the M mode and green button, I have permanant f/22 If I use one of the AE modes, I have permanant f/5. The "Tab" will move the auto aperture lever after the camera exposes wide open in AE mode. The aperture ring has somehow detached itself from the blades. Has anyone had this problem with an old lens, and can this be fixed by a pro who specializes in old lenses at reasonable prices?

04-23-2009, 11:01 PM	#11
jboyde Veteran Member Join Date: Apr 2009 Location: New York Posts: 328 Original Poster	Originally posted by res3567 Check this out. Just bought a lens from a guy on EBAY A Vivitar 100-300 f/5 Mounted it and played with it. Everytime I use the "Green button" (the equivalant of yor AE button on your K100D) the viewfinder would get dark. Took off the lens and turned the apeture ring,and the blades did not open up. The auto aperture works just great. If I use the M mode and green button, I have permanant f/22 If I use one of the AE modes, I have permanant f/5. The "Tab" will move the auto aperture lever after the camera exposes wide open in AE mode. The aperture ring has somehow detached itself from the blades. Has anyone had this problem with an old lens, and can this be fixed by a pro who specializes in old lenses at reasonable prices? Is it only with that lens? I wonder if older lenses affect the newer Pentax DSLRs because their "heavier" than newer ones. New cameras mainly use autoexposure so the blades and the levers arent manipulated as often, so the camera mechanics may be more delicate. Kinda like putting a new Toyota engine in a '74 Chevy Nova. Sure the engine is good for a car thats made out of fiberglass and aluminum but it doesnt have the torque for 2 tons of Detrot steel! Bad analogy?

04-23-2009, 11:11 PM	#12
res3567 Veteran Member Join Date: Sep 2008 Location: Houston Tx. Photos: Gallery Posts: 1,876	Originally posted by jboyde Is it only with that lens? I wonder if older lenses affect the newer Pentax DSLRs because their "heavier" than newer ones. New cameras mainly use autoexposure so the blades and the levers arent manipulated as often, so the camera mechanics may be more delicate. Kinda like putting a new Toyota engine in a '74 Chevy Nova. Sure the engine is good for a car thats made out of fiberglass and aluminum but it doesnt have the torque for 2 tons of Detrot steel! Bad analogy? Good Point! Well taken! This is a HEAVY lens. Another option to investigate. Havn't had time to FULLY explore all options. Thank You!

04-24-2009, 11:50 AM	#13
SOldBear Veteran Member Join Date: Feb 2009 Location: Alameda, CA Posts: 3,206	Originally posted by res3567 The aperture ring has somehow detached itself from the blades. Has anyone had this problem with an old lens, and can this be fixed by a pro who specializes in old lenses at reasonable prices? I had a Pentax SMC-M 100mm 1:2.8 with the same symptom. Technically, it's simple to fix. The problem with the lens I had was that the lever connecting the aperture ring and the aperture had been broken at the joint. I could not find the replacement part. So I used the lens as an organ donnor for other lenses. So whether it can be fix depends on what's broken. If something just comes loose, it's easy. If a part is broken, it's not easy.