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02-23-2009, 06:10 AM   #1
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M42 adapters on Me Super - metering shift !?

I have just got a Pentax Me Super from ebay and started to try some M42 lenses I got earlier. With M42 to Pentax K adapters, I am able to put old M42 lenses on my Me super. However, there is an annoying problem of metering shift. Based on tests I have done, the problem seems to be from the adapters.

I have two adapters, both are third party. One of them, which has no flange, makes the metering constantly 2 stops under correct exposure, and the othere, which has a flange, makes correct metering. They are tested with the same lens. Therefore, I come to realised that it is the adapters that are really making the problem. I wonder if anyone of you have encountered similar problem. Is this normal? Will a genuine adapter from Pentax solve the problem?

Please help. Many thanks!

Pei

02-23-2009, 06:26 AM   #2
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The adapter with the flange is not going to let you focus to infinity.

As to the meter values. Are you sure the meter is even correct. You may want to check that before testing lenses.
02-23-2009, 07:23 AM   #3
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Perhaps the battery is near dead and gives inconsistent readings. Or you have some basic malfunction. I never encountered any M42 metering problems with Pentax film cameras, especially not with these old modells, which have a very plain meter (no spot metering or sophisticated matrix metering, I mean). This simple center weighted metering usually works reliable with anything you put onto the mount...

Ben
02-23-2009, 07:37 AM   #4
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a few more details

Thanks for the words, folks!

I test the metering of that Me Super against my other cameras using the same lens, and the batteries are brand new. The adapter which has no flange makes a constant 2 stops metering shift. And what is interesting is that if you look through the viewfinder and turn the adapter, you can actually see the change of meter value (the more you turn it, the more metering shift there is).

By the way, the meter stays at very low position (most of the time at the bottom: 2S/4S) if there is no lens mounted, but it changes as soon as an adapter is put in (say, 1/30). There seems to be some kind of connection between the lens mount and the metering, which I cannot figure out.

02-23-2009, 07:54 AM   #5
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Look inside the camera, there's an armature that reads the K mount lens aperture. Perhaps the flanged adapter also engages this armature, pushing it as you screw the adapter in.
02-23-2009, 08:45 AM   #6
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QuoteOriginally posted by micahhsu Quote
Thanks for the words, folks!

I test the metering of that Me Super against my other cameras using the same lens, and the batteries are brand new. The adapter which has no flange makes a constant 2 stops metering shift. And what is interesting is that if you look through the viewfinder and turn the adapter, you can actually see the change of meter value (the more you turn it, the more metering shift there is).

By the way, the meter stays at very low position (most of the time at the bottom: 2S/4S) if there is no lens mounted, but it changes as soon as an adapter is put in (say, 1/30). There seems to be some kind of connection between the lens mount and the metering, which I cannot figure out.
Thanks for the additional info. That indeed sounds quite like Nester wrote: the adapter engages the aperture simulator lever - which it should not. I guess, it is a bit roughly made and a sharp corner just catches the lever. You can try to file that down - or buy a genuine Pentax adapter.

Ben
02-23-2009, 09:00 AM   #7
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From what I saw, the adapter SHOULD engage the meter, and actually push it all the way (as if it was a f/1.2 lens) then you meter the light with the diaphragm.
QuoteOriginally posted by Nesster Quote
Look inside the camera, there's an armature that reads the K mount lens aperture. Perhaps the flanged adapter also engages this armature, pushing it as you screw the adapter in.
02-23-2009, 09:27 AM   #8
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QuoteOriginally posted by titrisol Quote
From what I saw, the adapter SHOULD engage the meter, and actually push it all the way (as if it was a f/1.2 lens) then you meter the light with the diaphragm.
Huh? I have the Genuine Pentax Adapter in front of me as I type and it has no coupler. Edit: The preceding statement is WRONG! See below... End edit I have used this adapter on both of my non-A, K-mount bodies (both Ricohs made about the same time as the ME Super) with no metering issues.

For the original OP...Does you ME Super meter properly with K-mount lenses? It sounded from your posts as if you were determining the meter accuracy by comparison to other bodies. If you were doing the comparison using a K10D or K20D and your M42 lens, the ME Super is probably the more accurate of the two (assuming both bodies are functioning properly).

Steve

P.S. The coupler on the non-crippled K-mount never communicates absolute aperture to the camera. Instead, it communicates the degree of bias to apply to the current meter reading only. This was usually done using a variable resistor in the meter circuit.


Last edited by stevebrot; 02-24-2009 at 07:03 PM.
02-23-2009, 09:33 AM   #9
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QuoteOriginally posted by micahhsu Quote
Thanks for the words, folks!

I test the metering of that Me Super against my other cameras using the same lens, and the batteries are brand new. The adapter which has no flange makes a constant 2 stops metering shift. And what is interesting is that if you look through the viewfinder and turn the adapter, you can actually see the change of meter value (the more you turn it, the more metering shift there is).

By the way, the meter stays at very low position (most of the time at the bottom: 2S/4S) if there is no lens mounted, but it changes as soon as an adapter is put in (say, 1/30). There seems to be some kind of connection between the lens mount and the metering, which I cannot figure out.
I just read this post a little more carefully.

Normally, you should see a slight decrease in indicated shutter speed if you get any change at all when the adapter is inserted (smaller opening). Is there any indication of damage to the mount or mirror box? The coupler for the aperture follower lever should not touch the mount adapter. If it does, it is not in the proper position. Either that (as noted above) or the adapter is not properly machined.

Edit:

I am wrong, so WRONG!

I guess I never really looked carefully at the Genuine Pentax adapter when mounted on a non-crippled K-mount. The right side slot (facing camera) slips over the aperture ring coupler. When the adapter is properly mounted the coupler will be at full clockwise position indicating maximum aperture. This position should always the same regardless of what the actual maximum aperture is. My Pentax-M 200/4 at f/4 will position the coupler at the same location as my Pentax-M 50/1.7 at f/1.7. Too far clockwise and there is risk of damage and/or underexposure. Not far enough and you will get consistent overexposure.

End Edit

Steve

Last edited by stevebrot; 02-24-2009 at 07:12 PM.
02-23-2009, 05:13 PM   #10
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Thanks guys! I think I have figured it out!

There is a difference between the two adapters I have. The one with flange has a hole on the flange to lock it in the right position, but the one without flange obviously cannot do so. Therefore, when I mount the lens in with the latter, it passes the right position and goes in further, and it pushes the aperture value lever all the way to the end, which makes Me Super read the largest aperture of the lens as something around f1.0!

As there is no hole on the adapter to lock the position, an alternative may be to drill a hole on the bottom plate of the lens, which is something I do not like. And I doubt genuine Pentax M42 adapter can be free from this issue, since the condition is the same - no where to lock the position. Maybe I am wrong on this.

Anyone using genuine adapters on Me Super? If it can be locked in the right position, I will certainly get one; otherwise I will simply need to live with manual exposure/ASA compensation.

Last edited by micahhsu; 02-23-2009 at 05:31 PM.
02-24-2009, 03:32 AM   #11
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QuoteOriginally posted by micahhsu Quote
Thanks guys! I think I have figured it out!

There is a difference between the two adapters I have. The one with flange has a hole on the flange to lock it in the right position, but the one without flange obviously cannot do so. Therefore, when I mount the lens in with the latter, it passes the right position and goes in further, and it pushes the aperture value lever all the way to the end, which makes Me Super read the largest aperture of the lens as something around f1.0!

As there is no hole on the adapter to lock the position, an alternative may be to drill a hole on the bottom plate of the lens, which is something I do not like. And I doubt genuine Pentax M42 adapter can be free from this issue, since the condition is the same - no where to lock the position. Maybe I am wrong on this.

Anyone using genuine adapters on Me Super? If it can be locked in the right position, I will certainly get one; otherwise I will simply need to live with manual exposure/ASA compensation.
There is plainly something very wrong with your adapter. Any adapter made after the original Pentax one (those by Hama and Kood are more or less exact copies) and ofcourse the original Pentax adapter DO NOT NEED LOCKING HOLES! They are locked into place by a tiny spring, screwed to the adapter.

In fact, there cannot be a hole, as the adapter is completely inside the K-mount and ends flush with that, which renders the camera's locking pin useless.

It would be best, if you could post an image of this assembly, as it is rather pointless to continue this guesswork.

Ben
02-24-2009, 04:53 AM   #12
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I think the hole refers to a slot that engages the metering lever. Which tell the camera that the lens is fully open, and htne stop-down metering can be performed easily.
If my mechanics are correct the equivalent to f/1 occurs when the lever is moved all the way clockwise and thus the adapter should engage the lever in that manner.
02-24-2009, 06:11 PM   #13
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The ME super is my body of choice for screwmount lenses. But I'm a slave to aperture priority. With a pentax brand adapter, everything works perfect.
Ryan
02-24-2009, 07:19 PM   #14
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QuoteOriginally posted by stevebrot Quote
I just read this post a little more carefully.

Normally, you should see a slight decrease in indicated shutter speed if you get any change at all when the adapter is inserted (smaller opening). Is there any indication of damage to the mount or mirror box? The coupler for the aperture follower lever should not touch the mount adapter. If it does, it is not in the proper position. Either that (as noted above) or the adapter is not properly machined.

Edit:

I am wrong, so WRONG!

I guess I never really looked carefully at the Genuine Pentax adapter when mounted on a non-crippled K-mount. The right side slot (facing camera) slips over the aperture ring coupler. When the adapter is properly mounted the coupler will be at full clockwise position indicating maximum aperture. This position should always the same regardless of what the actual maximum aperture is. My Pentax-M 200/4 at f/4 will position the coupler at the same location as my Pentax-M 50/1.7 at f/1.7. Too far clockwise and there is risk of damage and/or underexposure. Not far enough and you will get consistent overexposure.

End Edit

Steve

As noted in the edits I made to my previous post, I was badly mistaken. Titrisol has it right regarding how the coupling engages. The correct position of the coupler should be at about the 4 o'clock position when the adapter is properly mounted. It should also be visible through the "slot" and flush with the face of the adapter. This position indicates maximum aperture and should be the same for all lenses when the aperture ring is set at maximum for that lens.

Steve

Last edited by stevebrot; 02-24-2009 at 07:33 PM.
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