Crippled mount?

I have come across this phrase a few times, here on the forum, and one or two other places, but I'm not entirely sure what it means.

Anybody care to enlighten me?

A horse with a lame leg? I've never heard of the term before. Not in the context of photography anyway

Taken from Wiki:

The "crippled" KAF2 mount is found on Pentax DSLRs released beginning with the K10D/K100D Super. It supports the extra features of the KAF2 mount including the two power contacts for the lens. Power zoom is supported (not full support and only in K10D), as well as lenses with focus motors. Such lenses support Supersonic Drive Motor (SDM), allowing for quieter autofocus. Like the "crippled" KAF mount, it does not have a mechanical stop-down coupler/indicator and thus can only use stop-down metering on pre-A lenses.

Ah!, I see. - Thank you.

My istD has a mechanical stop down coupler. So, I can meter at full aperture with an M or K lens, yes?... But later models can't do this!

Sounds like a backward step from Pentax. Why'd they do that?

Almost, depends on what you mean with full aperture.
The crippled one will meter at the lens wide open but it can't stop down to do a metering.
, so if you've a f/2.8 lens it will meter at that but if you've the aperture ring on f/5.6 you image will be underexpose.

Yes. I think I understand. Thanks.

PG and me have learned something!

To sell more new lenses of course.

Adding a little more to Stefans explanation, "K" mount lenses (and screw mount used via an adaptor) do not have the electrical contacts to relay lens informatiom to the body, so the body will have no idea what aperture is in use as this information is no longer relayed through the actuating lever used to stop the lens down at the firing stage.

"K" mount lenses were designed in the days when setting the aperture on the lens would result in the information been passed mechanically through the actuating lever to the body, with the advancement in electronics and the addition of electrical contact to the lens ("KA" mount), the need for the mechanical linkage eventually became redundant.

I'm fond of posting this link for anyone interested in the K mount evolution link

Another chart etc.etc.

link

Regards

Yes they can do it. The *ist D and all digital models have a crippled KAF or KAF2 mount. This means you can't normally use the camera in Av mode with M and K lenses except for the largest aperture. That's not the case with all film cameras.

See http://www.bdimitrov.de/kmp/technology/summary/index.html

That chart wrongly states that Av mode completely works with M & K lenses for the digital models. They should have put an Av" symbol instead of Av.

That's the diaphragm release. The *ist D doesn't have a stop down coupler, so the camera doesn't know what aperture is selected until it stops down. It has to physically stop down to meter, which you do via the Green button. You wouldn't need to do this if it had a stop down coupler.

I have just sent them a mail.

Regards

Or to reduce costs by removing support for long obsolete lenses (in the wider market's sense), or to make room for other technological developments that mean the mechanical coupling can no longer be accommodated.

When you press the "green button" it still closes down the aperture, I really don't understand why it can't take a reading then and when the lens is wide open (in rest) so that the camera knows the difference and calculate that.
I can't see why this can't be done.