[nucleon]

Link:
Can I use aperture ring of Pentax FA lens in aperture priority mode? - Photography Stack Exchange

Posted instructions (copy) from the link above. The M Mode + Green Botton have worked for me. It seems that now I can use my failed K-30.

Q:
Can I use aperture ring of Pentax FA lens in aperture priority mode?
I'm considering getting an FA Limited lens for my Pentax DSLR. The FA series has an aperture ring with an "A" setting for control by camera bodies that support it.
Can I instead use the aperture ring to set the actual aperture value in Av (aperture priority mode), letting the camera pick a shutter speed, or am I limited to the "A" aperture and have to use the thumb dials on the body to control aperture? I don't want to go full-manual mode.



A #1
To use aperture priority on Pentax dSLR with FA lens, you have to leave the aperture ring to "A" and select the aperture on body.
With aperture ring in A mode, the FA lens will behave just like a DA lens. You can use Av mode and set aperture on the body, shutter time will be calculated according to automatically measured exposure.
With aperture ring set on a specific aperture, the body does not know what you have set it to and would not be able to select shutter speed. By default, shutter will not work. You can enable using aperture ring in Custom Settings, but that will just enable using shutter - the lens will be used wide open regardless of the setting on aperture ring.
That's where the "crippled" part of the "crippled KAF2" mount on Pentax dSLR-s shows up - they do not have the mechanical linkage to read aperture settings from an aperture ring.

A #2

It's a shame; I would love to have a real aperture ring! Oh well, thanks for the tip. – Henry Jackson May 16 '11 at 12:46

@HenryJackson To get a real aperture ring that can be used in Av mode, you should get an older, non-A lens (e.g. something from SMC-M series). With such lens, the aperture selected will be in effect immediately. A Lensbaby with Sweet 35 Optics would also work similarly. – Imre May 16 '11 at 13:31
add a comment

A #3 !!!

Another thing to note about the use of the aperture ring when using manual lenses on Pentax bodies is that you'll need to press the green button to "stop down" before taking your shot. This triggers the aperture lever and so when you take your shot the lens properly closes rather than stays fully open. This procedure is required on the K series lenses. Via this method, the camera will be able to sense the proper light levels and offer a shutter speed. Note that this will only work in Manual mode. If you use Av, then the aperture will always be fully open. On the older non-automatic lenses (those without the aperture lever like the screw-mount lenses), when you stop down the iris will close and remain closed.

END

[grahame]

The answers are not 100% correct.

If you set the aperture ring on FA lens at the aperture you want, instead of "A", you get a "M/K" like lens. You can still fire the shutter, and if you sett the camera at "M", you can use green button to get semi-auto exposure.
Otherwise, if you set the camera at Av, and lens at, say F8.0, you can get wide-open image on normal functional camera, rather than an F8.0 picture you want;
And on your failed aperture unit, all pictures will still be dark, regardless what you set on lens or camera, because a failed aperture motor on camera will always leave the aperture fully closed during exposure. Unless you set your camera using the smallest aperture also.
With a camera having failed aperture unit, you can use M42 lenses, or those lenses modified by Canon users (aperture lever removed), so the malfunctioning aperture motor will not close the aperture.

[UncleVanya]

I'm confused. In manual aperture mode the most the lens can stop down is the aperture you set. So it can't underexpose by overextending the lever. However my failed aperture control block gave inconsistent results sometimes seeming to not depress the control arm enough resulting in overexposed shots.

[grahame]

The lens stops down by the spring inside; And the aperture motor on camera moves to the position where the lever should be stopped.
I guess there are different types of aperture motor failure, some may keep the lens wide open (could not move = overexposure) and some just let the aperture level go all the way (to minimum aperture, dark image).

[UncleVanya]

The lens stops down by the spring inside; And the aperture motor on camera moves to the position where the lever should be stopped.
I guess there are different types of aperture motor failure, some may keep the lens wide open (could not move = overexposure) and some just let the aperture level go all the way (to minimum aperture, dark image).

But again - in manual aperture I don't care how far you move it - it can't go all the way closed. Try it off camera. The lens will only close as far as the aperture ring is set to.

[grahame]

The lens will only close as far as the aperture ring is set to.

You are right.
To use the aperture ring on the lens, you can not use Av on camera. You will have to use M on camera. You set exposure, and set aperture manual on lens. Unless the camera has issue closing the aperture (you get wide open shot in this case), you should be able to get the exposure set as you want. -- a full manual way.

[richandfleur]

If you use a manual aperture ring equipped lens, in AV mode and set the aperture manually to the same as you have fixed the ring to, you should be able to meter correctly, with the camera selecting the appropriate ISO and shutter speed?

[grahame]

If you use a manual aperture ring equipped lens, in AV mode and set the aperture manually to the same as you have fixed the ring to, you should be able to meter correctly, with the camera selecting the appropriate ISO and shutter speed?

Nope. The lens will be kept wide open, unless the aperture motor is broken.
DSLR camera always keep the aperture wide open for AF, and close the aperture only during exposure to the F you set on camera.
Older film cameras could do what you described, but the DSLR simplified the mount and loss the ability to do that -- we call the new mount "crippled" mount.

[nucleon]

I have several manual lenses and without the Green Button none of them worked correctly. Now I am confused after all the posts and will try to repeat #3 instructions tomorrow without and with Green Button. As I pushed the Green Button the aperture closed and hen opened, No picture taken. Then the next picture was taken with correct exposure, I thought that I understood why and how :-)

[UncleVanya]

I have several manual lenses and without the Green Button none of them worked correctly. Now I am confused after all the posts and will try to repeat #3 instructions tomorrow without and with Green Button. As I pushed the Green Button the aperture closed and hen opened, No picture taken. Then the next picture was taken with correct exposure, I thought that I understood why and how :-)

With aperture ring set to anything other than A - you need to use Green Button. This will stop the aperture down, but only to the point you set the aperture to no farther (that's the key) which sets the exposure for you. You can then make changes to this exposure as you want. Every time you shoot the aperture should close using M mode - the question is how to meter. If you set your exposure without the green button (using external light meter for example) that should work also.

Av mode - lens will be open unless you have a lens with A and then the aperture control block could malfunction and press too far resulting in minimum aperture rather than what you selected.