[newarts]

The contact works, but seems a bit "precarious", if this didn't last, I will remember to try the thin copper wire tricks. Sound more "stable" (easier to get a good contact).

My contact seems precarious too but has lasted more than two years I think.

Lowell is right, the exposure is not correct. So if anyone plan to do this, bare the limitations in mind.

I kind of get confused at first, but manage to work out that when in use flash I can either have (if I am using M42 lens or pentax-M lens that are not fully mounted, so aperture ring at lens still close down the aperture):

It can be useful to put a notch on the M lens base before the existing notch so the lens will stop and be secured when not fully rotated.

- set aperture on camera to max, and set actual aperture on lens, which should give correct exposure

I preset the lens to the desired aperture and rotate the ewheel so aperture indicated in the viewfinder is fully open - then the camera will not attempt to close the lens' aperture at exposure time.

Strangely, for my vivitar 28mm f2, it works as expected at f2, f2.8 and f4. At f8 and beyond, I still need +1ev compensation. Will play around with this a bit more and see if my understanding is somehow wrong.

I see behavior like this sometimes & don't understand it!

[demp10]

I was guessing perhaps the actuator displacement scales would converge as you approach minimum aperture. Did you test it out to f/45?

I did not test at F45 but my calculations indicate that should need no compensation at either end, which makes sense.

[demp10]

I preset the lens to the desired aperture and rotate the ewheel so aperture indicated in the viewfinder is fully open - then the camera will not attempt to close the lens' aperture at exposure time.

If I understand it right, when you mount the lens, the camera body pushes the aperture lever so the lens is fully open. An unmount lens is normally closed to whatever aperture is set on the ring. For A lenses at the "A" position, it is simply the smallest aperture (e.g. F22 or F32). When the lens is mounted, even if you set the aperture at a smaller f-stop, the camera will force it to stay open wide.

When you take the photo, the camera moves the level proportionally to the F-stop selected by the camera dial. If you set the camera at wide open, it will not move the leaver and the lens will stay wide open even if you stopped it down using the aperture ring. On the other hand, if you set the camera, let's say at F16 and the lens at F5.6 through the ring, then when taking the photo, the camera will move the lever to the F16 distance, but the lens will close only to F5.6 since it is stopped at that.

The proper way to control the aperture though the camera, is to set the lens at the smallest aperture (which on A lenses is next to "A") to allow full movement of the level. The camera then will stop down the lens based on the f-stop dialed in the body. With the exception of fully open or fully closed F-stops, all other will have incorrect exposures on M or K lenses (with very few exceptions for late version of some M lenses with linear area apertures).

[newarts]

If I understand it right, when you mount the lens, the camera body pushes the aperture lever so the lens is fully open. An unmount lens is normally closed to whatever aperture is set on the ring. For A lenses at the "A" position, it is simply the smallest aperture (e.g. F22 or F32). When the lens is mounted, even if you set the aperture at a smaller f-stop, the camera will force it to stay open wide.

When you take the photo, the camera moves the level proportionally to the F-stop selected by the camera dial. If you set the camera at wide open, it will not move the leaver and the lens will stay wide open even if you stopped it down using the aperture ring. On the other hand, if you set the camera, let's say at F16 and the lens at F5.6 through the ring, then when taking the photo, the camera will move the lever to the F16 distance, but the lens will close only to F5.6 since it is stopped at that.

The proper way to control the aperture though the camera, is to set the lens at the smallest aperture (which on A lenses is next to "A") to allow full movement of the level. The camera then will stop down the lens based on the f-stop dialed in the body. With the exception of fully open or fully closed F-stops, all other will have incorrect exposures on M or K lenses (with very few exceptions for late version of some M lenses with linear area apertures).

The approach I use is a little different - it is based on m42 lenses in manual mode. The aperture ring is used to set the aperture on the lens & metering is done with the actual setting that'll be used when the shot is taken - there is no aperture lever to worry about with M42 lenses. M & K series lenses can be used the same way by not rotating the lens fully when mounting it. The lens' aperture lever is not contacted by the camera's lever, so the lens' aperture does not change as the photo is taken, ie. just like a fully manual lens.

My lenses are virtually all A type or M42 & the problem of M or K type lenses rarely arises for me in real life.

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Last edited by newarts; 02-01-2012 at 09:26 PM.

[Lowell Goudge]

If I understand it right, when you mount the lens, the camera body pushes the aperture lever so the lens is fully open. An unmount lens is normally closed to whatever aperture is set on the ring. For A lenses at the "A" position, it is simply the smallest aperture (e.g. F22 or F32). When the lens is mounted, even if you set the aperture at a smaller f-stop, the camera will force it to stay open wide.

good so far,

When you take the photo, the camera moves the level proportionally to the F-stop selected by the camera dial. If you set the camera at wide open, it will not move the leaver and the lens will stay wide open even if you stopped it down using the aperture ring.

be careful here, on an A lens out of A, the camera will treat it like any non A lens, and shoot wide open unless in Manual, and then the lever moves to full stopped down to let the lens determine the aperture

On the other hand, if you set the camera, let's say at F16 and the lens at F5.6 through the ring, then when taking the photo, the camera will move the lever to the F16 distance, but the lens will close only to F5.6 since it is stopped at that.

no, out of A mode the camera treats the lens like a K and allows it to stop down to the mechanical limit you set with the aperture ring, UNLESS we are discussing having the aperture pin shorted, then things get interesting. The camera moves the aperture lever to the position an A series lens would require for the camera set aperture, as you say, and the lens will limit aperture to it's own limit, or if the aperture setting on the camera is more restrictive, to the camera limit. Due to the differences in motion between A and Non A lenses this is any one's guess.

The proper way to control the aperture though the camera, is to set the lens at the smallest aperture (which on A lenses is next to "A") to allow full movement of the level. The camera then will stop down the lens based on the f-stop dialed in the body. With the exception of fully open or fully closed F-stops, all other will have incorrect exposures on M or K lenses (with very few exceptions for late version of some M lenses with linear area apertures).

correct. and even if you try to force the lens to an aperture, usually the camera is more restrictive for the linear A motion, so many F stops over expose because the camera never lets the lens stop down enough. I plotted and posted this curve once.

I think some third party lenses may also be linear, which complicates things. That would be an interesting experiment, since if someone posted a list of linear aperture third party K mount lenses, these would be ones that have the potential to be successfully modified.

[demp10]

UNLESS we are discussing having the aperture pin shorted, then things get interesting.

All my comments/thoughts were with the "A" pin shorted at the camera mount, so the camera thinks it has an A lens.

I always wondered why Pentax did not provide input of max/min f-stop along with focal length for manual lenses (and allow to save presets for your popular lenses for instant retrieval). They already ask for focal length so it is just another input.

Then they could treat any manual lens as and A lens and even compensate automatically for the non-linear area steps in the lever displacements calculation. The formulas are not that complicated. They could even have a lookup table for all their manual lenses with parameters and corrections, so all you have to do is pick the lens by name and have full auto control.

[Lowell Goudge]

All my comments/thoughts were with the "A" pin shorted at the camera mount, so the camera thinks it has an A lens.

I always wondered why Pentax did not provide input of max/min f-stop along with focal length for manual lenses (and allow to save presets for your popular lenses for instant retrieval). They already ask for focal length so it is just another input.

Then they could treat any manual lens as and A lens and even compensate automatically for the non-linear area steps in the lever displacements calculation. The formulas are not that complicated. They could even have a lookup table for all their manual lenses with parameters and corrections, so all you have to do is pick the lens by name and have full auto control.

I think it has to do that every lens has a different range of stops. The a series has both max and min aperture contacts to scale the movement. But yes it is only 2 inputs more

[seppstefano]

The approach I use is a little different - it is based on m42 lenses in manual mode. The aperture ring is used to set the aperture on the lens & metering is done with the actual setting that'll be used when the shot is taken - there is no aperture lever to worry about with M42 lenses. M & K series lenses can be used the same way by not rotating the lens fully when mounting it. The lens' aperture lever is not contacted by the camera's lever, so the lens' aperture does not change as the photo is taken, ie. just like a fully manual lens.

My lenses are virtually all A type or M42 & the problem of M or K type lenses rarely arises for me in real life.

Ciao all,
first post here since first-time Pentax dslr user . Yes, just got an oldie but goodie K-x, with standard kit 18-55 and 50-200, after having been a Canon 30D dslr user using only MF lenses (pentax, nikon, contax).

So far so good but was disappointed when I started getting exposure issues with my pentax K series and just devised the same solution of not rotating the lens fully and using them stopdown, just as was used to do on the 30D. I almost decided to:
- for each lens: drill a locking hole and add insulators according to http://www.robertstech.com/matrix.htm.
- place the foil under the A pin of the bajonet.

Any comment, idea, input would be very warmly welcomed!

TIA,

Stefano

P.S.: Yesterday evening I just took some shots with an old AF-D 35-70/2.8 which just locked in place (only some issue on the f/stop ring).

[seppstefano]

Hello,
I'm again getting a metering issue, even with stop down mode (i.e. lens can stop down, doesn't engage the in body simulator), Av mode and fixed ISO on a K-x.

While I get good images with the lens full open (a generic lens), with the same light, the showed evaluated time doesn't change even if I stop the lens down.

It seems the camera isn't metering but just assuming from simulator lever. If it is not engaged light evaluation stays firm although the lens has been stopped down.

What makes me angry is that the old and obsolete Canon 30D allows to shot in Av and stop down without any other issue aside from the relative loss of light when stopping down. Any idea, perhaps an insulator on the lens mount informing the camera of maximum aperture would do the trick? I'm stuck. It seems the camera is not metering in stop down. BTW everything works fine in usual auto everything and latest lenses, so it is not a camera issue.

Thank you again

[Lowell Goudge]

Hello,
I'm again getting a metering issue, even with stop down mode (i.e. lens can stop down, doesn't engage the in body simulator), Av mode and fixed ISO on a K-x.

While I get good images with the lens full open (a generic lens), with the same light, the showed evaluated time doesn't change even if I stop the lens down.

It seems the camera isn't metering but just assuming from simulator lever. If it is not engaged light evaluation stays firm although the lens has been stopped down.

What makes me angry is that the old and obsolete Canon 30D allows to shot in Av and stop down without any other issue aside from the relative loss of light when stopping down. Any idea, perhaps an insulator on the lens mount informing the camera of maximum aperture would do the trick? I'm stuck. It seems the camera is not metering in stop down. BTW everything works fine in usual auto everything and latest lenses, so it is not a camera issue.

Thank you again

In Av mode the camera only shoots wide open, you must use manual mode, that is all.

As for telling the camera about maximum aperture, etc, this thread goes through the whole story. To be breif;

K and M lenses have a different movement to the aperture mechanism than A lenses so metering and control even if the apertures are known is not accurate, I modified a lens like this, including the A pin and powted the results
The viewfinder/metering is not accurate and needs compensation for open aperture metering, this needs to be addressed

In short, use manual and live with it. You do not need to meter every shot, set up for the lighting and shoot until it changes, checking the histogram as you go

If you want to shoot in Av mode, with manual lenses you should be shooting with M42 lenses

[seppstefano]

Thank you Lowell,
but if I mount let's say a M or K lens not fully locked-in the lens stops down exactly like a M42 lens (when I turn the ring). So, what prevents the camera from correctly metering in stop down and Av?

How can the camera avoid detecting that EV has to be lowered when diaphragm is getting closed?

I'd love to use Av (fixed ISO) with lens in stop down, nothing fancy

If Canon 30D (no contacts on bajonet) can, I can only think that those unused (all short) pins may prevent the camera to alter the metering...

Am I barking at the wrong tree?

[JimJohnson]

Turn out that the mount ring and the contact pin A act as a "punch" and cut out a hole on the foil (kitchen aluminium foil). Should I use a ticker foil?

You are correct. The lens mount acts like a paper punch with the chad stuck in the hole. This works just fine. And unless you are in the habit of transporting your camera body without either an attached lens or body cap, it is doubtful the chad will just fall out. I've had one mounted in my K-r for going on 10 months. I could remove it in a few minutes if I wanted to do so with no damage whatsoever to my camera. I have yet to find any reason to to remove it.

[seppstefano]

Well, well.

I tried with not fully locked in K35/3,5: fine exposures at different f stops.
Then with a P50/1,7 (not engaging the simulation lever): wrong exposures. The exposure with the P50/1,7 was heavily underexposed, even at full aperture.

So I examined the lens mount.

The Zeiss lens mount sits flat flush to camera bajonet and surely does short all the pins.
Pentax lens mount have a different profile with a recessed central part (in section something looking like an "U" I__I) which, I bet, prevents the pins from being shorted.

Some nail polish is over a zeiss lens mount and I'll briefly report what happens... Should this experiment be successful, next step would of course be a proper insulation/shortening pattern which would inform the camera.

Edit: no good results. Still figuring how why...

[Lowell Goudge]

Thank you Lowell,
but if I mount let's say a M or K lens not fully locked-in the lens stops down exactly like a M42 lens (when I turn the ring). So, what prevents the camera from correctly metering in stop down and Av?

nothing, the camera behaves like it does with M42 in this case

How can the camera avoid detecting that EV has to be lowered when diaphragm is getting closed?

nothing to my knowledge

I'd love to use Av (fixed ISO) with lens in stop down, nothing fancy

If Canon 30D (no contacts on bajonet) can, I can only think that those unused (all short) pins may prevent the camera to alter the metering...

Am I barking at the wrong tree?

The Pentax camera should behave. You indicate, at least my *istD and K19D would do this, I don't know about K7 and K5 as there was some difference to lens sensing on those bodies but as far as I know that can work, I just prefer to use the K lenses in manual mode, meter once of a middle grey tone in the scene and then check the histogram as I shoot to make sure nothing has changed

[seppstefano]

Thank you Lowell,
of course your method is the most correct and prevents from unwanted under/overexposures due to different colors or reflections of the subject(s).

About my "unorthodox" attempt of using non pentax lenses in continuous stop down mode, I guess that my problem is caused by either all-shorted pins (the shape of metal mount pentax lenses seems to me recessed and not allowing pins to make contact) or/and by some mechanical interference between zeiss lens and pentax camera levers.

Similar to what found and declared by Leitax the issue has different effects on different lenses, although I couldn't devise hard interferences. I'll keep trying to understand, anyway

Ciao,

Stefano