Manual apature stop-down metering?

**NaClH2O** · 03-22-2011, 02:28 PM

Originally posted by Ira

No noise on mine with Ev. I'm also curious whether this a K lens that will only shoot wide open.

The main thing is, with anything before Pentax M lenses, the camera is incapable of changing the aperture of the lens because the lens can't do it. There is nothing "electrically connected" to change the manually set (by hand) aperture of, let's say, a Super Takumar.
All the cam can do is change ISO and shutter speed for correct metering.

True but a "K" lens is designed to be focused wide open. Even if your lens is set to f/8 (or f/22 for that matter) you focus wide open because there is so much more light that way. When you push the green or e/v button the camera does 2 things. 1 the camera stops down the lens to the aperture you set (by moving the small tab on the back of the lens) and 2. It takes a reading at that aperture. You are then able to take your photo. There is no electrical connection but there is a mechanical one.

NaCl(clever people these Japanese)H2O

**NaClH2O** · 03-22-2011, 02:30 PM

Originally posted by Ira

Are you guys telling me that the mirror has to flip up for metering on the K-x?

No that was my bad. That is what you get when you are trying to do 5 things at the same time. I apologize.

NaCl(there is nothing so much fun as monitoring a field modification, ordering parts and trying to post on PF at the same time)H2O

jolepp · 03-22-2011, 02:33 PM

Hmm ... I seem to recall that the k-x does not bother to operate the aperture lever when green button metering in M-mode if the lens has a non-conductive base.

Chonker · 03-22-2011, 02:34 PM

The little metal tab works okay, smooth and easy to move, this is what the camera body lets go of to stop it down I guess?

If I look directly down the lens I can see it's held open (I can see the mirror clearly) and when I press the shutter I can see it stop down to take the picture. There is also a large brightness difference in two pictures taken with the same settings with the apature ring set differently so it's definitely working in this regards.

**NaClH2O** · 03-22-2011, 02:37 PM

Originally posted by jolepp

Hmm ... I seem to recall that the k-x does not bother to operate the aperture lever when green button metering in M-mode if the lens has a non-conductive base.

How does it work then? I know that the lens focuses wide open, I haven't shot with a manual lens in a while with my K-x, but I don't ever remember it focusing while stopped down. Will it work only with the e/v button?

NaCl(even I'm confused now)H2O

jolepp · 03-22-2011, 02:38 PM

Originally posted by Ira

Are you guys telling me that the mirror has to flip up for metering on the K-x?

It does not have to but for some reason it does if a lens has a conductive base and the auto pin is not shorted (or so I would recall

).

**NaClH2O** · 03-22-2011, 02:39 PM

Originally posted by Chonker

The little metal tab works okay, smooth and easy to move, this is what the camera body lets go of to stop it down I guess?

If I look directly down the lens I can see it's held open (I can see the mirror clearly) and when I press the shutter I can see it stop down to take the picture. There is also a large brightness difference in two pictures taken with the same settings with the apature ring set differently so it's definitely working in this regards.

OK take a picture of a bright scene at f8 or so and see if it comes out. If you don't have anything else shoot at a relative bright lamp.

NaCl(it should work)H2O

Chonker · 03-22-2011, 02:43 PM

Originally posted by jolepp

Hmm ... I seem to recall that the k-x does not bother to operate the aperture lever when green button metering in M-mode if the lens has a non-conductive base.

That sounds like it could be the trouble then.

These are the two lenses I've tried, the one on the left is the new one which I'm having troubles with.

jolepp · 03-22-2011, 03:05 PM

Originally posted by Chonker

That sounds like it could be the trouble then.

These are the two lenses I've tried, the one on the left is the new one which I'm having troubles with.

Yup, the one on the left seems to have a painted / coated base which would do it. The logic of this escapes me

. Some people report using a piece of aluminium tape at the base to short the contacts as a chromed base would. Slipping a piece of aluminium foil in there when mounting the lens so that it shorts the contacts could be used verify whether this is about the contacts being shorted (I would further recall that shorting any of them would make a difference).

Chonker · 03-22-2011, 03:05 PM

The black surface is definitely not conductive (had a go at it with a multi-meter). Now I'm wondering if strategically placed aluminised tape would fix that, is there a diagram anywhere explaining what the different pins on the lens do? (so i can avoid exploding anything)

**NaClH2O** · 03-22-2011, 03:05 PM

Chonker, try Ira's method of pusing the e/v button instead of the green button. I know that one of the two works as I took a bunch of shots last fall with the K-x and the Pentax K 125 f2.5 they all came out pretty much perfectly metered.

NaCl(even tho it was kinda dark and I was shooting at 3200 iso)H2O

jolepp · 03-22-2011, 03:08 PM

Shorting the pins is what happens with a chromed base (M/K lenses) so there should be no harm in it. This should explain pin functions: Features and Operation of the Ka Mount.

**NaClH2O** · 03-22-2011, 03:09 PM

Originally posted by Chonker

The black surface is definitely not conductive (had a go at it with a multi-meter). Now I'm wondering if strategically placed aluminised tape would fix that, is there a diagram anywhere explaining what the different pins on the lens do? (so i can avoid exploding anything)

The pins should just ground out, just as if you had a chromed base.

NaCl(they can't do anything anyway with a completely manual lens)H2O

Chonker · 03-22-2011, 03:10 PM

is that the button with the +/- symbol, I've tried and it does nothing either (no noises or change in shutter speed at different apertures)

Chonker · 03-22-2011, 03:31 PM - **1 Like**

Success!

Bit of aluminium tape did the trick, it's a little stiff to mount the lens but meters a treat

Looking forward to a nice day to give this a go, if it's any good it'll be a proper bargain.

Thanks for all your help, that's a neat bit of knowledge to have about the metallic bases!

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03-22-2011, 02:28 PM	#16
NaClH2O Site Supporter Join Date: Sep 2006 Location: Bronx NY Photos: Gallery \| Albums Posts: 5,631	Originally posted by Ira No noise on mine with Ev. I'm also curious whether this a K lens that will only shoot wide open. The main thing is, with anything before Pentax M lenses, the camera is incapable of changing the aperture of the lens because the lens can't do it. There is nothing "electrically connected" to change the manually set (by hand) aperture of, let's say, a Super Takumar. All the cam can do is change ISO and shutter speed for correct metering. True but a "K" lens is designed to be focused wide open. Even if your lens is set to f/8 (or f/22 for that matter) you focus wide open because there is so much more light that way. When you push the green or e/v button the camera does 2 things. 1 the camera stops down the lens to the aperture you set (by moving the small tab on the back of the lens) and 2. It takes a reading at that aperture. You are then able to take your photo. There is no electrical connection but there is a mechanical one. NaCl(clever people these Japanese)H2O

03-22-2011, 02:30 PM	#17
NaClH2O Site Supporter Join Date: Sep 2006 Location: Bronx NY Photos: Gallery \| Albums Posts: 5,631	Originally posted by Ira Are you guys telling me that the mirror has to flip up for metering on the K-x? No that was my bad. That is what you get when you are trying to do 5 things at the same time. I apologize. NaCl(there is nothing so much fun as monitoring a field modification, ordering parts and trying to post on PF at the same time)H2O

03-22-2011, 02:33 PM	#18
jolepp Veteran Member Join Date: Oct 2010 Location: Finland Photos: Albums Posts: 3,196	Hmm ... I seem to recall that the k-x does not bother to operate the aperture lever when green button metering in M-mode if the lens has a non-conductive base.

03-22-2011, 02:34 PM	#19
Chonker New Member Join Date: Mar 2011 Posts: 9 Original Poster	The little metal tab works okay, smooth and easy to move, this is what the camera body lets go of to stop it down I guess? If I look directly down the lens I can see it's held open (I can see the mirror clearly) and when I press the shutter I can see it stop down to take the picture. There is also a large brightness difference in two pictures taken with the same settings with the apature ring set differently so it's definitely working in this regards.

03-22-2011, 02:37 PM	#20
NaClH2O Site Supporter Join Date: Sep 2006 Location: Bronx NY Photos: Gallery \| Albums Posts: 5,631	Originally posted by jolepp Hmm ... I seem to recall that the k-x does not bother to operate the aperture lever when green button metering in M-mode if the lens has a non-conductive base. How does it work then? I know that the lens focuses wide open, I haven't shot with a manual lens in a while with my K-x, but I don't ever remember it focusing while stopped down. Will it work only with the e/v button? NaCl(even I'm confused now)H2O

03-22-2011, 02:38 PM	#21
jolepp Veteran Member Join Date: Oct 2010 Location: Finland Photos: Albums Posts: 3,196	Originally posted by Ira Are you guys telling me that the mirror has to flip up for metering on the K-x? It does not have to but for some reason it does if a lens has a conductive base and the auto pin is not shorted (or so I would recall ).

03-22-2011, 02:39 PM	#22
NaClH2O Site Supporter Join Date: Sep 2006 Location: Bronx NY Photos: Gallery \| Albums Posts: 5,631	Originally posted by Chonker The little metal tab works okay, smooth and easy to move, this is what the camera body lets go of to stop it down I guess? If I look directly down the lens I can see it's held open (I can see the mirror clearly) and when I press the shutter I can see it stop down to take the picture. There is also a large brightness difference in two pictures taken with the same settings with the apature ring set differently so it's definitely working in this regards. OK take a picture of a bright scene at f8 or so and see if it comes out. If you don't have anything else shoot at a relative bright lamp. NaCl(it should work)H2O

03-22-2011, 02:43 PM	#23
Chonker New Member Join Date: Mar 2011 Posts: 9 Original Poster	Originally posted by jolepp Hmm ... I seem to recall that the k-x does not bother to operate the aperture lever when green button metering in M-mode if the lens has a non-conductive base. That sounds like it could be the trouble then. These are the two lenses I've tried, the one on the left is the new one which I'm having troubles with.

03-22-2011, 03:05 PM	#24
jolepp Veteran Member Join Date: Oct 2010 Location: Finland Photos: Albums Posts: 3,196	Originally posted by Chonker That sounds like it could be the trouble then. These are the two lenses I've tried, the one on the left is the new one which I'm having troubles with. Yup, the one on the left seems to have a painted / coated base which would do it. The logic of this escapes me . Some people report using a piece of aluminium tape at the base to short the contacts as a chromed base would. Slipping a piece of aluminium foil in there when mounting the lens so that it shorts the contacts could be used verify whether this is about the contacts being shorted (I would further recall that shorting any of them would make a difference).

03-22-2011, 03:05 PM	#25
Chonker New Member Join Date: Mar 2011 Posts: 9 Original Poster	The black surface is definitely not conductive (had a go at it with a multi-meter). Now I'm wondering if strategically placed aluminised tape would fix that, is there a diagram anywhere explaining what the different pins on the lens do? (so i can avoid exploding anything)

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03-22-2011, 03:05 PM	#26
NaClH2O Site Supporter Join Date: Sep 2006 Location: Bronx NY Photos: Gallery \| Albums Posts: 5,631	Chonker, try Ira's method of pusing the e/v button instead of the green button. I know that one of the two works as I took a bunch of shots last fall with the K-x and the Pentax K 125 f2.5 they all came out pretty much perfectly metered. NaCl(even tho it was kinda dark and I was shooting at 3200 iso)H2O

03-22-2011, 03:08 PM	#27
jolepp Veteran Member Join Date: Oct 2010 Location: Finland Photos: Albums Posts: 3,196	Shorting the pins is what happens with a chromed base (M/K lenses) so there should be no harm in it. This should explain pin functions: Features and Operation of the Ka Mount.

03-22-2011, 03:09 PM	#28
NaClH2O Site Supporter Join Date: Sep 2006 Location: Bronx NY Photos: Gallery \| Albums Posts: 5,631	Originally posted by Chonker The black surface is definitely not conductive (had a go at it with a multi-meter). Now I'm wondering if strategically placed aluminised tape would fix that, is there a diagram anywhere explaining what the different pins on the lens do? (so i can avoid exploding anything) The pins should just ground out, just as if you had a chromed base. NaCl(they can't do anything anyway with a completely manual lens)H2O

03-22-2011, 03:10 PM	#29
Chonker New Member Join Date: Mar 2011 Posts: 9 Original Poster	is that the button with the +/- symbol, I've tried and it does nothing either (no noises or change in shutter speed at different apertures)

03-22-2011, 03:31 PM - 1 Like	#30
Chonker New Member Join Date: Mar 2011 Posts: 9 Original Poster	Success! Bit of aluminium tape did the trick, it's a little stiff to mount the lens but meters a treat Looking forward to a nice day to give this a go, if it's any good it'll be a proper bargain. Thanks for all your help, that's a neat bit of knowledge to have about the metallic bases!