[markoneswift]

Hi all, can someone please tell me what I'm doing wrong ? I'm trying to use my Pentax-A 70-210 F/4 on my K-x and I've used it successfully many times, but tonight I CANNOT select an aperture other than wide open ! I'm in Manual as usual, A mode disengaged on lens, aperture lever works iris fine off camera, but I mount the lens and the iris opens and stays open. This is also going on with my Tamron 70-210 F/3.8-4 adaptall lens - mounts with fully open aperture and unable to change the aperture dial.


I think my brain must have gone bad because I've used these lenses fine before, but now - not !! Help ??!!

[NZ_Ross]

I think my brain must have gone bad because I've used these lenses fine before, but now - not !! Help ??!!

It is 5th on November - Guy Fawkes night in NZ. I think the trick is - take the fireworks out of the mirror box, it will probably work much better

[Giklab]

A mode disengaged on lens

There's your problem.

[Fogel70]

The camera will hold the aperture fully open until exposure. Have you checked what happen when you capture a shot?

[Digitalis]

The camera will hold the aperture fully open until exposure.

...or better yet, select an aperture of f/8 and hold down the Green button. The aperture blades should be visible.

[markoneswift]

A mode disengaged on lens is what I want - I want to manually control aperture so that is not a problem. I don't want to hold down the green button to see the aperture blades - that won't work if the lens isn't in A mode will it ?

---------- Post added 11-05-15 at 01:56 AM ----------

It is 5th on November - Guy Fawkes night in NZ. I think the trick is - take the fireworks out of the mirror box, it will probably work much better

I'm trying to get fireworks IN my mirror box mate :-)

[Digitalis]

I don't want to hold down the green button to see the aperture blades - that won't work if the lens isn't in A mode will it ?

Yes you do, and it should visibly stop the lens down. The green button it is what allows people to use stop down metering. The camera has to stop the lens down to get an accurate metering value for your selected aperture when your lens isn't set to the "a" mode. If you can see the aperture blades that will show if your lens/camera is working properly or not.

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Last edited by Digitalis; 11-05-2015 at 02:09 AM.

[Adam]

Hi all, can someone please tell me what I'm doing wrong ? I'm trying to use my Pentax-A 70-210 F/4 on my K-x and I've used it successfully many times, but tonight I CANNOT select an aperture other than wide open ! I'm in Manual as usual, A mode disengaged on lens, aperture lever works iris fine off camera, but I mount the lens and the iris opens and stays open. This is also going on with my Tamron 70-210 F/3.8-4 adaptall lens - mounts with fully open aperture and unable to change the aperture dial.


I think my brain must have gone bad because I've used these lenses fine before, but now - not !! Help ??!!

It's supposed to stay open until the exposure. Just set the ring to "A", select the desired aperture, and it should be used when you release the shutter. There's no way to get a K-mount lens to work as if it had a manual diaphragm.

[Na Horuk]

Go to Menu, scroll to back, and Enable Aperture ring use. Turn off camera; on the lens, there is an aperture ring, press the A button on it, and place the aperture setting to A. Leave it there forever. This allows the camera to choose the aperture, and you can choose it through the camera. You no longer need to touch the lens, except for manual focus.

In M mode, you need to have single ISO number (like ISO 200, not range like Auto ISO 100-1600). Using a lens without selecting A on aperture ring (or older K-mount lens that doesn't have that) will only let you use M in fully manual, single ISO mode. This will let the camera stop down the lens to the selected aperture (on the lens ring), but the camera does not actually know the chosen aperture, so it cannot do any calculations with it (this is why metering must be done through green button, where camera stops down and takes a reading)
All other modes default to Av, which has continuous metering, allows ISO range, but never stops down the lens.
Both of these problems disappear once you select A mode on aperture ring. This makes the lens behave practically like modern DA lenses (except it might not have autofocus)

Generally speaking, you want aperture to be wide open while you focus the photo, as DoF is most shallow when wide open. This means your focusing is most accurate. Then the camera will stop down lens to chosen aperture once the trigger is pressed. You can use DoF preview (check camera manual) if you want.

[markoneswift]

OK thanks for the tips everyone, very much appreciated. I'm coming from a few years of Sony NEX use, where I was using the live view screen with fully manual prime lenses and I got used to using the aperture ring and watching the histogram on screen for metering. I can see the effect of the 'optical preview' green button fine with my Tamron lens as it is a fully manual lens - my confusion was trying to use Aperture priority so manual with 'green button' stop-down metering seems to work fine.
I do also have a Pentax-A lens and I still cannot get that to behave properly though - I think there may be a mechanical issue with it so I'm going to investigate.
Thanks again, great tips and great forum :-)

[Lowell Goudge]

A mode disengaged on lens is what I want - I want to manually control aperture so that is not a problem. I don't want to hold down the green button to see the aperture blades - that won't work if the lens isn't in A mode will it ?

---------- Post added 11-05-15 at 01:56 AM ----------




I'm trying to get fireworks IN my mirror box mate :-)

If A mode is disengaged you need to go into the settings and select aperture ring, or the camera thinks nothing is attached and will not activate the diaphram lever,

Once that is done, you can force shutter speed with the green button in manual mode, or check exposure using DOF preview without changing settings, but A mode is much better because the metering is a ton better in A mode.

Also A mode lets you use P-TTL flash metering, if you have A mode available there is no justifiable reason to manually use the aperture ring

[Digitalis]

my confusion was trying to use Aperture priority so manual with 'green button' stop-down metering seems to work fine.

I told you to use the green button.

I do also have a Pentax-A lens and I still cannot get that to behave properly though - I think there may be a mechanical issue with it so I'm going to investigate.

If it happens to be a Pentax SMC-A 50mm f/1.7 - that is a lens that has a bit of notoriety with aperture control issues.

[markoneswift]

I told you to use the green button.



If it happens to be a Pentax SMC-A 50mm f/1.7 - that is a lens that has a bit of notoriety with aperture control issues.

It's not mate, it's an A 70-210 F/4. A previous owner tried cleaning fungus out of it and accidentally remove the aperture 'click' stops. All other aspects of the lens seem fine and, after testing, it does work OK in manual with stop down metering. A mode doesn't work, so I suspect the previous owner has stuffed the mount contact.

[ChristianRock]

By the way, if you are using the aperture ring to select the aperture (not leaving it on A), you can ONLY use M (Manual) mode. Aperture Priority (and any other automatic mode) will always shoot the lens wide open regardless of what you setting you have on your aperture ring.