[MikeS]

In my experience with a K-x, it is the DATA pin which must be shorted for your purposes.

Now that you say that, I tried shorting each contact pin (without a lens on, obviously), and it stopped down regardless of which pin I was shorting.... seemingly as long as at least one was shorted, it thinks there's a lens... interesting

[jheu02]

I'll just throw this in to keep the can o' worms open a bit longer. Don't the K20D and K-x (or any modern Pentax for that matter) all have the same KA2 crippled mount? If so, seems like the only reason I could think of would be firmware.

[newarts]

.....
.... however, the tubes are John's, so I'll try to hold off attacking his equipment with duct tape for the time being

Plain old aluminum foil works well too!

[Silverkarn]

I'm still not exactly sure what the definition of stop-down metering is. But when i use Extension tubes with my Pentax K-x i can see the depth of field in the viewfinder without pushing any buttons.

When i turn the aperture dial the depth of field changes in the viewfinder, and the green button sets the proper shutter speed. The only problem i have is sometimes the image is so dark in the viewfinder i cannot see properly to focus correctly.

[MikeS]

without pushing any buttons

That's different. What kind of lens are you using? And any idea about what setting you're using to stop-down the aperture in real time (instead of upon the shutter release)?

[Silverkarn]

That's different. What kind of lens are you using? And any idea about what setting you're using to stop-down the aperture in real time (instead of upon the shutter release)?

Using a Sigma Macro 28-80 auto focus lens. The extension tubes are your basic metal tubes, no electrical connections. I set the aperture wheel to my desired Aperture and "what i see is what i get". Camera forces me to be in Aperture Priority i believe.

If there is no aperture lever on the extension tubes there is NO WAY for the camera to move the aperture on the lens, AT ALL

I dont know about your friends camera, but there is physically no way for the camera to move the aperture without an aperture lever on the extension tube.

[MikeS]

tubes are your basic metal tubes

Hmm, haven't played with the tubes very much, but it could be (as suggested earlier) that the metal part is the problem (or rather, a lack of [conductive] metal). The camera seems to sense a lens' presence if pins are shorted (by contacting any conductive metal, having electrical connections or not--I used a key while the lens was off, and it tried to stop down=it sensed that a 'lens' was there). But I'll be able to tinker more the next time I use the tubes...

I'd be interested to know how you got it to show DOF in the viewfinder all the time (like a constant DOF preview). I glanced through the settings and didn't see anything pertaining to it....

[Silverkarn]

Hmm, haven't played with the tubes very much, but it could be (as suggested earlier) that the metal part is the problem (or rather, a lack of [conductive] metal). If the pins aren't shorted (by contacting any conductive metal, having electrical connections or not--I used a key while the lens was off, and it tried to stop down). But I'll be able to tinker more the next time I use the tubes...

I'd be interested to know how you got it to show DOF in the viewfinder all the time (like a constant DOF preview). I glanced through the settings and didn't see anything pertaining to it....

>_> I just slapped on the extension tube, the macro lens, set "allow aperture ring" to on and started shooting. I thought there was something wrong with my viewfinder at first because it was so dark, then i realized that my aperture was closing when i turn the ring, and i was used to the aperture being wide open all of the time as on my 18-55 kit lens.

And my extension tubes have a matte paint covering the whole thing. Its your basic black 3-4 dollar extension tubes from Ebay.

I need to ask. What, exactly, are you expecting your camera to do with the extension tubes on?

[Jodokast96]

Could just be that once you get the lens attached to the end of the tubes, there's enough flex in the mount to keep from making contact to short the pins. I occasionally get this when using a heavier lens and a full set of tubes. In my case, I have tubes with contacts, so I can watch my aperture setting flick on and off on my top display. Doesn't happen with my lighter lenses or if using only a single tube.

[Hypocorism]

I think it would, if pin#2 was not shorted. In practice it seems that the lenses with the lever have a conductive (chomed) base, and the non-conductive bases go with M42 lenses such as the Takumars (there is some sort of coating on the metal bases, apparently). I know of no really convincing explanation as to why treat lenses differently based on this, though :-) Other quirks of the k-x body would seem to be raising the mirror with green button metering and also treating lenses with the aperture ring A position indicator pin shorted/not shorted (e.g. A vs. M) differently for AWB (at least).

Is this an explanation for what you are describing?

Pentax K mount - Wikipedia, the free encyclopedia

.R.

[Lowell Goudge]

there was a similar thread to this a while back regarding the K7 and Vivitar Auto Extension tubes which have black paint or anodizing. What is required is to remove the insulating surface that would contact the pins, I removed all of it, out of ease to do this, and the stopped down worked.

I do not recall this issue on my K10D or *istD, but regardless it does not impact anything really

[jheu02]

To clear up what may be a little confusion, here are the tubes in question, your basic set of PK mount auto extension tubes. They are black aluminum, though I guess that's just the anodized coating.

On my K20, in Manual mode, I get stop down metering when pushing the green button (Use Aperture Ring - set to on), i.e. camera will set an appropriate shutter speed based on stopping down the aperture to what the ring on the lens is set to.

On Mike's K-x, when he tries to perform the same function, the aperture doesn't stop down with tubes attached between the mount and lens. If only the manual lens is mounted to the camera, it stops down normally for the meter reading.

On my K20, manual mode, no lens attached, the aperture lever will actuate when the green button is depressed whether or not I short any of the pins, i.e. the camera body doesn't care that nothing's attached, it will try to meter by actuating the aperture lever on the body

On Mike's K-x, this apparently does not happen except when he shorts a pin. So, it sounds to me like it's a firmware issue with the K-x, i.e. it will only actuate the aperture lever if there's conductive metal attached to the mount. I verified that the black coating is non-conductive with my DMM set to a continuity test mode.

I also checked some spots where there was some brassing or bare aluminum exposed and the continuity checked good. So, I suppose I could scratch the anodized coating so his K-x would recognize them, or I could just let him hang and get his own set. Hmmm....

[jolepp]

Is this an explanation for what you are describing?

Pentax K mount - Wikipedia, the free encyclopedia

.R.

Not really, the question is: why does green button metering work differently depending on whether the lens shorts pin(s) on the mount or not?

[MikeS]

So, it sounds to me like it's a firmware issue with the K-x, i.e. it will only actuate the aperture lever if there's conductive metal attached to the mount.

Well, it seems like this answers the question at hand, as far as why it won't stop-down meter with the tubes.

the question is: why does green button metering work differently depending on whether the lens shorts pin(s) on the mount or not?

I guess we'd have to ask Pentax for the answer as to why they designed it this way. But at least I know now what my issue is.

Interesting thoughts nonetheless. It isn't like there aren't ways around this, and I may play with some settings later, if I try the tubes again.
Thanks to everyone for all the input and discussion. Very enlightening

[MikeS]

I suppose I could scratch the anodized coating so his K-x would recognize them

Thanks John! You're a real trooper