[jocko_nc]

I had it happen with my new Beck 135 lens. My SMC-M's always seem to find the correct shutter speed when in Av mode. This Beck is always underexposed. I switched to M mode and found the correct shutter speed, the photos were great.

I know they are "M" series, but they do have a mechanical aperture link. ???.

I don't know the answer, just that that Beck lens is to be used in M mode.

[ryan s]

I just tried 3 M42 lenses, but couldn't duplicate the result. I've seen it with a lens, but can't remember which...could have been an M style lens.

As for why...no idea...

[troyz]

using the jupiter - 9 (m42 mount using an adaptor) at wide open makes the camera think it is shooting at F1.4, and i think this is impacting on its metering.

anyone have any similar experience with M42 lenses?

Consulting table 1 in

Features and Operation of the Ka Mount

I gotta think your m42 adaptor/lens combination is shorting the "r3" contact (and possibly others) on the lens mount.

The VL125 "2.5 reads as 2.4" issue is totally different; whether the body reads the contact pattern on the VL125's mount as 2.5 or 2.4 is arbitrary.

[Miserere]

I'm with troyz, you're shorting something.

[Gooshin]

i think i got it..

the jupiter is an all metal lens, and its base is wide enough to cover all the electrical contacts (including the pin, which is why my hole drilling technique works)

so the thing just shorts all of the contacts at once.

egad!

[rparmar]

You don't need to make swiss cheese of it. Four more holes and you've got a 1.0 lens!

[Lowell Goudge]

also i would like to note,

the jupiter has no connections and no aperture lever, so as far as i know the camera is simply measuring light hitting the sensor... hmmm

is it possible that a FF lens is giving the cropped sensor more light in relative terms? (hope that made sense?)

I forget what camera body you have, but note,

The K10D has a real issue with metering and manual lenses. I have tested several things and have made from these tests the following conclusion.

The K10D focusing screen causes the metering to be very irregular as a function of apature of the lens. If you take a 50mm F1.4 lens, and meter wide open, it under exposes by about 1-1.5 stops. If you use stopped down metering, and check each apature detent, the metering improves at between F4 and F5.6, but by F8/F11 it is over exposing by 1.5 to 2 stops. Ultimately by F22/32 it comes back a little (perhaps only +1.5 stops.

This behavior holds true even for a new lens, when you take it out of A mode.

BUT if you install an *istD screen in the K10D the metering behaves exactly the same as an *istD.

This leads me to believe the focusing screen on the K10D has a tendancy to scatter light a little, and it scatters more light when lenses are wide open, causing the metering to see more light than is actually reflected at the point the metering is directed at, resulting in under exposure, and less light when stopped down (causing over exposure). The reason it is reading correctly at F4-F5.6 is this is the normal range of maximum apature in consumer lenses today, hence it is biased to read correclty for this apature. The camera uses the maximum apature information from the lens to apply the corection factor for other maximum apatures.

Now, back to your initial posting and the camera thinking it has an F1.4 lens mounted. Does the camera show an apature value? if so, there is either something that is sticking down from the lens into your body right at the pin location for automatic apature as this pin should be recessed into the mount, or the pin in your camera body is either shorted to the mount or sticking out too far, and contacting the flange on the lens.

The AE pin must contact the flange (or a pin protruding from the lens) to make the camera think it is an AE lens. If this connection is made, then I would need to look at the contact information to tell you what all other pins shorted is interpreted as on the K mount.

[ryan s]

i think i got it..

the jupiter is an all metal lens, and its base is wide enough to cover all the electrical contacts (including the pin, which is why my hole drilling technique works)

so the thing just shorts all of the contacts at once.

egad!

My Vivitar touches all the contacts (ooo naughty), and I didn't check, but I bet the Sears does as well.

BUT if you install an *istD screen in the K10D the metering behaves exactly the same as an *istD.

The newer screen is designed to be "brighter" for the user. As we've discussed before, and as you've mentioned in your post, new cameras tend to be most accurate between f/4 and f/7.1-ish since most of the lenses fall into this range.

I have an LI-60 in mine, and the metering has improved, but only slightly. Enough so that I can salvage mildly over-exposed pictures. I like how dark it is, and everything tends to "snap" into focus with it. 100% worthwhile upgrade

[georgweb]

ryan s said:

I like how dark it is,

Anyway I just wanted to 3rd troyz opinion about the contacts,
Manual Focus Forum / M42 on K100D, pin assignment, auto-iso, focus trap

With the recessed pin contacted it should be possible to get the shutter-release-trap on AF mode working, as well as Auto-ISO, with ANY lens attached, should you find a ways to close those contacts like you need it. Matrix metering could work also then.

I've been seriously thinking about shortcut-options for those contacts, like a small dip-switch-panel on the exterior.

BTW I just shot the Jup-9 yesterday, black anodized version, gives me the same behaviour like 90% of my manual lenses, open EV ca. 0 - +0,5, closed down ca. +1,5 - +2,0. Viewfinder shows: F--

Georg

[Lowell Goudge]

ryan s said:



Anyway I just wanted to 3rd troyz opinion about the contacts,
Manual Focus Forum / M42 on K100D, pin assignment, auto-iso, focus trap

With the recessed pin contacted it should be possible to get the shutter-release-trap on AF mode working, as well as Auto-ISO, with ANY lens attached, should you find a ways to close those contacts like you need it. Matrix metering could work also then.

I've been seriously thinking about shortcut-options for those contacts, like a small dip-switch-panel on the exterior.

BTW I just shot the Jup-9 yesterday, black anodized version, gives me the same behaviour like 90% of my manual lenses, open EV ca. 0 - +0,5, closed down ca. +1,5 - +2,0. Viewfinder shows: F--

Georg

A very long time ago now (just after I joined the forum) I experimented with converting a NON AE lens to AE.

I did this successfully, in terms of making the function work, controlling the apature, getting matrix metering etc. BUT (and it is a big one) there is an issue with lenses prior to KA mount that makes this useless, or nearly so. On K mounts, the apature changes diameter linearly with movement of the activation lever, but on KA mount lenses the apature area changes linearly with the activation lever. As a result although you can sort of control the apature with the camera the result is not close enough to be a workable function.

[richard64]

This has happened to me too with some M series lens

That is impossible. M lenses do have a coupler to feedback the aperture ring setting to the camera, but the K100D and Super do not have a corresponding coupler. So regardless of the position of the aperture ring, the camera will not know what aperture is used. Further, M lenses do not have electrical contacts, instead, there is a bare metal face, so they short all the contacts on the body (this is how the camera knows that you are using an K or M lens).

However, the diaphragm is stopped down by the camera when you take a shot since M lenses have a diaphragm actuator. The way that this works is like this: when you attach the lens the aperture is pulled fully open the aperture actuator (this is pulled against a spring so that in the rest position the diaphragm is closed). When you turn the aperture ring it effectively sets an end-stop, when you take a shot the actuator coupler in the camera stops pulling against the spring in the lens which pulls the diaphragm to the end-stop set by the aperture.

However, for an A lens (in the A position) the camera will move the actuator the appropriate amount when you take the shot. It knows how far to move the actuator by the electrical contacts on the A lens - some conduct and some do not and these indicate the max and min aperture of the lens, so the camera knows the aperture when the lens is wide open (which is the case once you have attached the lens) and it knows how much to move the actuator to get a specified aperture.

This raises the question: why not paint on the M lens plate so that the correct code is sent to the camera, and so now the camera will be able to determine how much to move the actuator? Unfortunately this is not possible. The reason is that for A lenses and later, the actuator moves in proportion to the area of the iris (and so, it is proportional to the f-number), and this is how the Pentax digital cameras work. Whereas for M lenses the diaphragm actuator moves in proportion to the diameter of the iris. So even if you tell the camera the max and min aperture of the lens, since the camera will always move the actuator in proportion to the f-number you will not get the correct aperture with an M lens.

So, the camera will know that you have a K or M lens (because all the contacts are shorted) but it knows that for K and M lenses it cannot determine the max and min value of the aperture and it cannot determine the position of the aperture ring. So it should give F-- for all K and M lenses. (Unless, of course, your camera is faulty in some way.)

Richard

[stevebrot]

...Further, M lenses do not have electrical contacts, instead, there is a bare metal face, so they short all the contacts on the body (this is how the camera knows that you are using an K or M lens)...

Richard,
That is not quite true. My Jupiter-9 has a non-conductive base as do most Takumars and many other M-42 lenses. It is "lack of data" rather than shorted contacts that clues the body that it does not have an "A" type lens attached. You can demonstrate this removing your lens and turning the camera on.

There is also a general misconception regarding the aperture information coupling on K-series and M-series lenses. The original K-mount had a "follower" ring in the body that engaged with a recessed tab attached to the aperture ring in the lens. That "follower" ring was mated to a variable resistor such that movements of the "follower" ring could be used to apply a bias to the meter voltage to allow full-open metering. The aperture ring determined the position of the "follower" ring, which in turn biased the meter to allow for accurate exposure. The whole system was quite elegant and versatile and was based entirely upon analog electronics (no computer used or needed).

The important point to understand is that metering and aperture-priority automation was done without sending any actual f/stop information to the body. This feature (in the form of max/min aperture) was added to the A-series and later lenses by means of electrical contacts to allow for programmed exposure automation. More contacts were later added to support automatic focus.

Note also that this meter coupling feature is not the same as the linear/non-linear behavior of the aperture actuator (two different pieces of hardware). As you correctly stated, The aperture actuator lever behaves basically like a switch in K-series and M-series lenses. Aperture is either open or closed. On the other hand, in the A-series mounts the amount of travel of this lever determines the the f/stop at time of exposure.

Steve

[Lowell Goudge]

That is impossible. M lenses do have a coupler to feedback the aperture ring setting to the camera, but the K100D and Super do not have a corresponding coupler. So regardless of the position of the aperture ring, the camera will not know what aperture is used.

the lens contacts do not feed any apature information to the camera, all they do is tell the maximum and minimum apature so that the camera knows the range

Further, M lenses do not have electrical contacts, instead, there is a bare metal face, so they short all the contacts on the body (this is how the camera knows that you are using an K or M lens).

this is not correct. in fact the knowledge of an "A" lens is based upon the shorting of one specific pin only to the base, this pin is recessed in the mount, and requires a protruding male pin on the lens to contact it. on origonal A series lenses, this was a sliding pin that was pushed down a little when the A position was selected

However, the diaphragm is stopped down by the camera when you take a shot since M lenses have a diaphragm actuator. The way that this works is like this: when you attach the lens the aperture is pulled fully open the aperture actuator (this is pulled against a spring so that in the rest position the diaphragm is closed). When you turn the aperture ring it effectively sets an end-stop, when you take a shot the actuator coupler in the camera stops pulling against the spring in the lens which pulls the diaphragm to the end-stop set by the aperture.

However, for an A lens (in the A position) the camera will move the actuator the appropriate amount when you take the shot. It knows how far to move the actuator by the electrical contacts on the A lens - some conduct and some do not and these indicate the max and min aperture of the lens, so the camera knows the aperture when the lens is wide open (which is the case once you have attached the lens) and it knows how much to move the actuator to get a specified aperture.

This raises the question: why not paint on the M lens plate so that the correct code is sent to the camera, and so now the camera will be able to determine how much to move the actuator? Unfortunately this is not possible. The reason is that for A lenses and later, the actuator moves in proportion to the area of the iris (and so, it is proportional to the f-number), and this is how the Pentax digital cameras work. Whereas for M lenses the diaphragm actuator moves in proportion to the diameter of the iris. So even if you tell the camera the max and min aperture of the lens, since the camera will always move the actuator in proportion to the f-number you will not get the correct aperture with an M lens.

this is not possible because regardless of whether you paint over the places, or drill them, a flat lens plate will never contact the recessed "A" pin on the body mount.

So, the camera will know that you have a K or M lens (because all the contacts are shorted) but it knows that for K and M lenses it cannot determine the max and min value of the aperture and it cannot determine the position of the aperture ring. So it should give F-- for all K and M lenses. (Unless, of course, your camera is faulty in some way.)

Richard

actually it will fisplay F-- for any lens that is taken out of the "A" position because that opens the contact to the "A" pin on the mount. FYI it is the thirtd pin from the lens locking pin, and is recessed.

[stevebrot]

the lens contacts do not feed any apature information to the camera, all they do is tell the maximum and minimum apature so that the camera knows the range

...the knowledge of an "A" lens is based upon the shorting of one specific pin only to the base, this pin is recessed in the mount, and requires a protruding male pin on the lens to contact it...it will fisplay F-- for any lens that is taken out of the "A" position because that opens the contact to the "A" pin on the mount. FYI it is the thirtd pin from the lens locking pin, and is recessed.

Thank you Lowell for the accurate description of what the "A" contacts do and how they work.

Steve