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05-19-2013, 11:43 AM   #1
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M42 to K Adapter tampering with metering (MF Film SLRs)?

Not another M42-adapter thread!

It is kind of hard to explain for me, but maybe you will know what I am talking about.

When using my Kipon M42 adapter (which features a nice inside flange to depress the pin to close the lenses aperture; haven't seen that one on the original Pentax adapter) on a film era K-mount body, the adapter's notch that moves the body's aperture lever (which would tell the camera the desired aperture if you would use an open aperture metering M lens) most likely doesn't travel to the optimal position when I attach the adapter and screw a lens into it.

In order to replicate the metering that my digital body gives me for a selected aperture (I used an evenly lit white wall as reference and triple compared the results that the metering system of each camera gave me), I need to turn the adapter back a few degrees, otherwise the picture would end up underexposed by as much as two stops in some cases. This means that when I find the right angle for the adapter, I need to be very careful when attaching the lens, so that I won't turn the adapter past the "sweet spot" again. In practice this means, that before taking any picture, I have to "re-calibrate" my camera/adapter/lens combination each time I switch lenses, endlessly comparing what the light meter tells me to what my digital camera (which I don't even want to have with me all the time) tells me. You can imagine that switching between lenses becomes a real pain.

Did anyone of you notice similar behaviour with your adapters of different brands? Is it a common problem? Does the genuine Pentax adapter magically not turn too far? Is there a trick on how to do it correctly? Where about is the "absolute zero" for the lever? How do people, who recommend getting rid of the spring that keeps the adapter from getting loose do it (I imagine a loose adapter to be even less accurate)?

The whole thing really keeps me from enjoying my Helios 44 and my 35 mm SMC Tak on my MX and ME. I don't want to be restricted to using them only on a digital body in a reliable way.. Maybe I am over analyzing stuff, so please tell me.

Just as a side note, this doesn't affect the use of the adapter on a digital body at all. The digital body doesn't feature this special lever, so there is no way to confuse it. It will just assume that the lens is wide open, even if it's not, meter the ligth that falls in through the lens, set/recommend the shutter speed accordingly and that's it, no problem.

05-19-2013, 12:01 PM   #2
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As long as you set the diaphragm to manual and ensure that the lever isn't being moved, you should be able to get proper metering without having to do anything else.

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05-19-2013, 01:59 PM   #3
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You are correct in that the adapter should move the follower on the body to position about 170 degrees opposite the red index on the lens mount. With a K-mount lens mounted, the position or this lever represents the current lens aperture and provides a reference offset to the meter. Moving it a few degrees will affect the reading, even when doing stop-down metering.

That being said, are you sure the metering from your reference dSLR is correct? You did not say whether your readings with the dSLR were done with the M42 lenses or with a more modern A, FA, or DA series lens. With the exception of M mode on the recent models, erratic stop-down metering on Pentax dSLRs is pretty much the rule. If possible, I would repeat your meter test with a hand-held meter or using the film body with a non-M42 lens.


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05-19-2013, 02:13 PM   #4
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I just compared what the original Pentax adapter, and the Kipon adapter do with that lever.

The slot in the adapter is dragging the follower all the way (about 70 deg.). With this function there is no difference between the two adapters.
And it seems even with a bent follower or damaged adapter the follower couldn't escape that movement.

So I don't think there is something wrong with the adapter (at least nothing that could produce this misbehaving).

By the way, removing the spring/screw when you use the original Pentax adapter with a Pentax film body is not such a good idea. Without a lens attached, this adapter sits very loose inside the body, and the spring loaded follower can prevent the adapter staying in the "screwed in" position, making it difficult to attach a lens. With DSLRs and some models of the last series of film bodies this problem does not exist ("crippled" mount).

EDIT:
You should also check whether the aperture in your M42 lenses isn't "slow" (delayed closing), or the flange of the Kipon doesn't always grab the aperture actuator of the M42 auto lens correctly. This could happen if the actuator doesn't move all the way out anymore (spring may have become tired). And, if the problem is only with one body, the resistor in the body giving the information about the follower position could be dirty. But in this case, you would face the same problem with M and A lenses.


Last edited by RKKS08; 05-19-2013 at 02:28 PM.
05-24-2013, 09:18 AM   #5
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QuoteOriginally posted by Adam Quote
As long as you set the diaphragm to manual and ensure that the lever isn't being moved, you should be able to get proper metering without having to do anything else.
The lever will be moved as soon as the adapter is attached to the camera body. If I would use only one lens for one roll of film and would be careful not to move the adapter (and thus the lever), it wouldn't really matter much, you are right. In that case the exposure on single pictures on the film would be pretty consistent and could be easily compensated for when developing or printing negatives.

QuoteOriginally posted by RKKS08 Quote
You should also check whether the aperture in your M42 lenses isn't "slow" (delayed closing), or the flange of the Kipon doesn't always grab the aperture actuator of the M42 auto lens correctly. This could happen if the actuator doesn't move all the way out anymore (spring may have become tired). And, if the problem is only with one body, the resistor in the body giving the information about the follower position could be dirty. But in this case, you would face the same problem with M and A lenses.
The lens blades are not sticky at all on both lenses (Helios and Tak) and the 35 mm Takumar is really very snappy while I also paid attention not to accidently have its Manual/Auto switch in the wrong position. The Kipon adapter permanently engages the "aperture actuator", so that the aperture will always be stopped down. I even made sure that the adapter was really pushing the pin in far enough since there is a little space between the inside flange that pushes the pin in and the bottom of the lens that is screwed in. I used a small blade to push it in even further, but the lenses were already closed down as far as possible, so this can't be the source of error.

I finally got the time and somewhat consistent light again to compare three lenses. The Helios 44-4 55mm f2, the SMC Tak 35mm f3.5 both on the M42 adapter and the SMC M 50mm f1.7. I used my Pentax ME because it has nice red LEDs in the viewfinder. I tried all lenses against a white wall that I pointed a lamp at, while it was rather cloudy outside, so I guess the light didn't really change dramatically during the time of the test.
On both M42 lenses the light meter gave me a reading of 1/125s at f5.6. When I opened the lenses up half a step (I guess that would be f4.5?), the meter would jump up to 1/250s (which means it would stay at 1/125 at f6.3 and fall to 1/60 at f8, which it also did in practice). I aimed at the same spot (thankfully there are a few spots) with all lenses and the results of the M42 lenses gave me confidence that my method was somewhat reliable. When I put on my K-mount M 50mm though, the light meter would suggest 1/60s at f5.6 and only go up to 1/125 when opened up to f4, which tells me that the adapter will lead the camera to under expose somewhere between half a stop and a full stop.
Gripping th lens and turning the adapter inside the body backwards a little, I could compensate for that and reproduce the metering that the K-mount lens had given me (and which I double checked using that same lens on my DSLR. Had to switch to spot metering, though. I guess the center weighted metering back in the day was a little more harsh than nowadays.).

My Impression still is that at least the Kipon adapter has too much play in the camera body. By removing that spring, you would make it even worse and I guess that is true for any adapter. I guess since most people use their adapters on digital bodies, anyway, it is not noticable since the exact position of the adapter is not that important (no lever here, camera in Av mode simply registers the light that is coming through correctly, no matter if stopped down or not), as long as it keeps your lens from falling off and any light from falling in.

Anybody else tried any adapters on MF bodies? What are your impressions?

Last edited by Arvid; 05-24-2013 at 09:30 AM.
05-27-2013, 12:06 PM   #6
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QuoteOriginally posted by Arvid Quote
Anybody else tried any adapters on MF bodies? What are your impressions?
I use the genuine Pentax adapter with my M-42 lenses and have not noticed any particular problems with my K-mount film cameras, though to be honest, I have never done any comparison readings.


Steve
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