Problem with aperture control - Pentax-M 50mm f1.7

Bui · 01-02-2017, 04:55 AM

Hello,

First of all Happy New Year to all of you

I have a Pentax-M 50mm f1.7 that stayed in my cabinet for a long time, I took it out today to play, and I realize something weird: when stopping down, the viewfinder darkens (it behave like a M42 lens) on my K-x. I have some K lenses that doesn't close the aperture when stopping down, only when I press the green button for metering, and taking picture, this M 50mm I used months ago when I started photography so I don't remember how it behaved back then. Does the lens have some problem (like a stuck aperture stick), can this problem be fixed? or this is the characteristic of the lens?

Thank you.

**Tonytee** · 01-02-2017, 05:03 AM - **1 Like**

Originally posted by Bui

Hello,

First of all Happy New Year to all of you

I have a Pentax-M 50mm f1.7 that stayed in my cabinet for a long time, I took it out today to play, and I realize something weird: when stopping down, the viewfinder darkens (it behave like a M42 lens) on my K-x. I have some K lenses that doesn't close the aperture when stopping down, only when I press the green button for metering, and taking picture, this M 50mm I used months ago when I started photography so I don't remember how it behaved back then. Does the lens have some problem (like a stuck aperture stick), can this problem be fixed? or this is the characteristic of the lens?

Thank you.

Hello. The only green button on the lens is to be pushed in, in order to the aperture ring into the "A" or Automatic Mode. Then you will need to push the same button in again in order to take the ring out of "A" or Automatic Mode. What happens when you take the aperture ring out of A Mode and move the ring back and forth?

Tony

**patrick9** · 01-02-2017, 05:10 AM - **1 Like**

Originally posted by Bui

Hello,

First of all Happy New Year to all of you

I have a Pentax-M 50mm f1.7 that stayed in my cabinet for a long time, I took it out today to play, and I realize something weird: when stopping down, the viewfinder darkens (it behave like a M42 lens) on my K-x. I have some K lenses that doesn't close the aperture when stopping down, only when I press the green button for metering, and taking picture, this M 50mm I used months ago when I started photography so I don't remember how it behaved back then. Does the lens have some problem (like a stuck aperture stick), can this problem be fixed? or this is the characteristic of the lens?

Thank you.

My K55/1.8 stops down ( gets darker just long enough for meter reading) with the green button, if the iso is set in manual. If in auto iso it does not. That is in M mode on the camera.

Bui · 01-02-2017, 05:15 AM

Originally posted by Tonytee

Hello. The only green button on the lens is to be pushed in, in order to the aperture ring into the "A" or Automatic Mode. Then you will need to push the same button in again in order to take the ring out of "A" or Automatic Mode. What happens when you take the aperture ring out of A Mode and move the ring back and forth?

Tony

Hello, mine is a M so there is no A level on the lens. The stop down metering work fine with my K 55 f2 so this is probably the problem of the lens (if there is). Just to be clear this is not a problem of not stopping down or not metering, and actually this is not a serious one that affect the use, but I find it weird that the viewfinder darkens when I stop down (that mean the lens really stops down when I change the aperture, not like my usual K lens when it does nothing, just stop down when metering and taking picture).

D1N0 · 01-02-2017, 05:18 AM - **1 Like**

This would happen when the aperture lever doesn't catch in the camera. Maybe somebody adapted the lens by taking out or cutting of the lever or it is bent.

pschlute · 01-02-2017, 05:24 AM - **1 Like**

Show us a picture of the rear of the lens

Not a Number · 01-02-2017, 06:14 AM - **1 Like**

Originally posted by Bui

I have a Pentax-M 50mm f1.7 that stayed in my cabinet for a long time, I took it out today to play, and I realize something weird: when stopping down, the viewfinder darkens (it behave like a M42 lens) on my K-x.

Have you used the lens before putting in the cabinet? Did it behave differently then?

Bui · 01-02-2017, 06:26 AM

Now I get your idea, I examine the rear of the lens and it seems exactly as you say. The M is on the right and the K is on the left. The lever of the M is too low, yeah maybe the previous owner cut it off (why did he do that?).

Is there any chance that this can be fixed?

Thank you.

HarisF1 · 01-02-2017, 06:35 AM - **1 Like**

Probably to make it act like an M42 lens or to use it on another camera model such as Canon to avoid hitting the mirror.

pschlute · 01-02-2017, 06:35 AM - **1 Like**

He probably cut it off so the lens now behaves like a M42 lens. It will stop down as you change aperture, which means the viewfinder will get darker, but on the plus side you can now use Av mode to expose your pictures.

You could try and find a damaged/fungus ridden M 50 1.7 on ebay and swap out the aperture lever yourself. Or just buy a working one...they are not expensive and will cost less than taking to a repair man/finding a donor lens.

---------- Post added 01-02-2017 at 01:38 PM ----------

Originally posted by D1N0

This would happen when the aperture lever doesn't catch in the camera. Maybe somebody adapted the lens by taking out or cutting of the lever or it is bent.

Good guess Sherlock !

Not a Number · 01-02-2017, 06:54 AM - **1 Like**

The DIY repair other than finding a donor part would be to silver solder or rivet a brass piece to extend the lever.

Sell the lens on the market place and note the condition of the lever. There are many MF shooters that find Av mode indispensable. These shooters might be interested in the neutered lens. Or someone may want it for parts.

HarisF1 · 01-02-2017, 07:24 AM - **1 Like**

I'd say you should probably keep it and treat it like an M42 lens. There's no need to lose out on a bit of money just to have to use the green button!

Bui · 01-02-2017, 07:49 AM

Actually I'm not thinking about selling or getting rid of it, for most of the time I won't hqve problem except for maybe when using a very small aperture, it will be hard to see the object. If fixing it requires buying another one for part I will probably do nothing.

This is the first time I know that a M42 lens can be used in AV mode (I'm a newbie), please tell me how, or I just switch to AV mode and shoot? How do the camera know the aperture?

Thank you.

HarisF1 · 01-02-2017, 07:56 AM - **1 Like**

Simply switch to Av mode and shoot. The camera doesn't need to know the aperture, it takes a light reading through the stopped down lens so will give a well exposed image most of the time.

Try to focus wide open, then stop down to shoot with this lens and your M42 lenses.

**UncleVanya** · 01-02-2017, 08:13 AM - **1 Like**

Just twist to open aperture and focus then twist to desired aperture and shoot when in Av mode.

01-02-2017, 04:55 AM	#1
Bui Veteran Member Join Date: Nov 2016 Photos: Gallery Posts: 316	Problem with aperture control - Pentax-M 50mm f1.7 Hello, First of all Happy New Year to all of you I have a Pentax-M 50mm f1.7 that stayed in my cabinet for a long time, I took it out today to play, and I realize something weird: when stopping down, the viewfinder darkens (it behave like a M42 lens) on my K-x. I have some K lenses that doesn't close the aperture when stopping down, only when I press the green button for metering, and taking picture, this M 50mm I used months ago when I started photography so I don't remember how it behaved back then. Does the lens have some problem (like a stuck aperture stick), can this problem be fixed? or this is the characteristic of the lens? Thank you.

01-02-2017, 05:10 AM - 1 Like	#3
patrick9 Site Supporter Join Date: Feb 2011 Location: Murfreesboro Tennessee Photos: Gallery \| Albums Posts: 3,458	Originally posted by Bui Hello, First of all Happy New Year to all of you I have a Pentax-M 50mm f1.7 that stayed in my cabinet for a long time, I took it out today to play, and I realize something weird: when stopping down, the viewfinder darkens (it behave like a M42 lens) on my K-x. I have some K lenses that doesn't close the aperture when stopping down, only when I press the green button for metering, and taking picture, this M 50mm I used months ago when I started photography so I don't remember how it behaved back then. Does the lens have some problem (like a stuck aperture stick), can this problem be fixed? or this is the characteristic of the lens? Thank you. My K55/1.8 stops down ( gets darker just long enough for meter reading) with the green button, if the iso is set in manual. If in auto iso it does not. That is in M mode on the camera. Last edited by patrick9; 01-02-2017 at 05:14 AM. Reason: spelling

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01-02-2017, 05:03 AM - 1 Like	#2
Tonytee Loyal Site Supporter Join Date: Jul 2012 Photos: Gallery \| Albums Posts: 21,505	Originally posted by Bui Hello, First of all Happy New Year to all of you I have a Pentax-M 50mm f1.7 that stayed in my cabinet for a long time, I took it out today to play, and I realize something weird: when stopping down, the viewfinder darkens (it behave like a M42 lens) on my K-x. I have some K lenses that doesn't close the aperture when stopping down, only when I press the green button for metering, and taking picture, this M 50mm I used months ago when I started photography so I don't remember how it behaved back then. Does the lens have some problem (like a stuck aperture stick), can this problem be fixed? or this is the characteristic of the lens? Thank you. Hello. The only green button on the lens is to be pushed in, in order to the aperture ring into the "A" or Automatic Mode. Then you will need to push the same button in again in order to take the ring out of "A" or Automatic Mode. What happens when you take the aperture ring out of A Mode and move the ring back and forth? Tony

01-02-2017, 05:15 AM	#4
Bui Veteran Member Join Date: Nov 2016 Photos: Gallery Posts: 316 Original Poster	Originally posted by Tonytee Hello. The only green button on the lens is to be pushed in, in order to the aperture ring into the "A" or Automatic Mode. Then you will need to push the same button in again in order to take the ring out of "A" or Automatic Mode. What happens when you take the aperture ring out of A Mode and move the ring back and forth? Tony Hello, mine is a M so there is no A level on the lens. The stop down metering work fine with my K 55 f2 so this is probably the problem of the lens (if there is). Just to be clear this is not a problem of not stopping down or not metering, and actually this is not a serious one that affect the use, but I find it weird that the viewfinder darkens when I stop down (that mean the lens really stops down when I change the aperture, not like my usual K lens when it does nothing, just stop down when metering and taking picture).

01-02-2017, 05:18 AM - 1 Like	#5
D1N0 Pentaxian Join Date: May 2012 Location: --- Photos: Gallery Posts: 6,802	This would happen when the aperture lever doesn't catch in the camera. Maybe somebody adapted the lens by taking out or cutting of the lever or it is bent.

01-02-2017, 05:24 AM - 1 Like	#6
pschlute Moderator Loyal Site Supporter Join Date: Mar 2007 Location: Surrey, UK Photos: Gallery Posts: 8,211	Show us a picture of the rear of the lens

01-02-2017, 06:14 AM - 1 Like	#7
Not a Number Moderator Join Date: Mar 2012 Location: Venice, CA Posts: 10,526	Originally posted by Bui I have a Pentax-M 50mm f1.7 that stayed in my cabinet for a long time, I took it out today to play, and I realize something weird: when stopping down, the viewfinder darkens (it behave like a M42 lens) on my K-x. Have you used the lens before putting in the cabinet? Did it behave differently then?

01-02-2017, 06:26 AM	#8
Bui Veteran Member Join Date: Nov 2016 Photos: Gallery Posts: 316 Original Poster	Now I get your idea, I examine the rear of the lens and it seems exactly as you say. The M is on the right and the K is on the left. The lever of the M is too low, yeah maybe the previous owner cut it off (why did he do that?). Is there any chance that this can be fixed? Thank you.

01-02-2017, 06:35 AM - 1 Like	#9
HarisF1 Veteran Member Join Date: Apr 2016 Posts: 543	Probably to make it act like an M42 lens or to use it on another camera model such as Canon to avoid hitting the mirror.

01-02-2017, 06:35 AM - 1 Like	#10
pschlute Moderator Loyal Site Supporter Join Date: Mar 2007 Location: Surrey, UK Photos: Gallery Posts: 8,211	He probably cut it off so the lens now behaves like a M42 lens. It will stop down as you change aperture, which means the viewfinder will get darker, but on the plus side you can now use Av mode to expose your pictures. You could try and find a damaged/fungus ridden M 50 1.7 on ebay and swap out the aperture lever yourself. Or just buy a working one...they are not expensive and will cost less than taking to a repair man/finding a donor lens. ---------- Post added 01-02-2017 at 01:38 PM ---------- Originally posted by D1N0 This would happen when the aperture lever doesn't catch in the camera. Maybe somebody adapted the lens by taking out or cutting of the lever or it is bent. Good guess Sherlock !

01-02-2017, 06:54 AM - 1 Like	#11
Not a Number Moderator Join Date: Mar 2012 Location: Venice, CA Posts: 10,526	The DIY repair other than finding a donor part would be to silver solder or rivet a brass piece to extend the lever. Sell the lens on the market place and note the condition of the lever. There are many MF shooters that find Av mode indispensable. These shooters might be interested in the neutered lens. Or someone may want it for parts.

01-02-2017, 07:24 AM - 1 Like	#12
HarisF1 Veteran Member Join Date: Apr 2016 Posts: 543	I'd say you should probably keep it and treat it like an M42 lens. There's no need to lose out on a bit of money just to have to use the green button!

01-02-2017, 07:49 AM	#13
Bui Veteran Member Join Date: Nov 2016 Photos: Gallery Posts: 316 Original Poster	Actually I'm not thinking about selling or getting rid of it, for most of the time I won't hqve problem except for maybe when using a very small aperture, it will be hard to see the object. If fixing it requires buying another one for part I will probably do nothing. This is the first time I know that a M42 lens can be used in AV mode (I'm a newbie), please tell me how, or I just switch to AV mode and shoot? How do the camera know the aperture? Thank you.

01-02-2017, 07:56 AM - 1 Like	#14
HarisF1 Veteran Member Join Date: Apr 2016 Posts: 543	Simply switch to Av mode and shoot. The camera doesn't need to know the aperture, it takes a light reading through the stopped down lens so will give a well exposed image most of the time. Try to focus wide open, then stop down to shoot with this lens and your M42 lenses.

01-02-2017, 08:13 AM - 1 Like	#15
UncleVanya Loyal Site Supporter Join Date: Jul 2014 Photos: Gallery \| Albums Posts: 28,445	Just twist to open aperture and focus then twist to desired aperture and shoot when in Av mode.