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02-08-2010, 02:49 AM   #1
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Lens with A setting

HI All

can anyone explain to me exactly how the A position on a lens works??

The reason i ask is that i have lens (2 in fact) that have A settings but the camera K7 doesnt seem to recognise that it has an A setting and treats it as a manual lens.

Although i can use it like this i would like to try an rectify whatever problem the lens has.

Adrian

02-08-2010, 02:51 AM   #2
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Moved to Beginners Corner.
02-08-2010, 02:56 AM   #3
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You actually have to set the aperture ring to the "A" position, by turining it and pressing the small button on the aperture ring to overcome the lock. The aperture ring locks if set to A or set to any of the manual aperture numbers.

If you dial in any of the aperture numbers, the camera will only recognize a manual lens. That is also true for later autofokus lenses with a real aperture ring.

Ben
02-08-2010, 02:56 AM   #4
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HI Brit

not sure that beginers corner is the right place for this......im trying to get a techincal explanation on how the A setting works (so i can try and repair it)

02-08-2010, 03:00 AM   #5
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bi Ben
sorry didnt see your reply.......yeah i know how to use a manual lens on the camera, but what i am trying to understand is what the camera is looking for ......for example it it looking for a resistance reading through the aperture pin (or something similar??)
02-08-2010, 03:05 AM   #6
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QuoteOriginally posted by milesy Quote
HI All

can anyone explain to me exactly how the A position on a lens works??

The reason i ask is that i have lens (2 in fact) that have A settings but the camera K7 doesnt seem to recognise that it has an A setting and treats it as a manual lens.

Although i can use it like this i would like to try an rectify whatever problem the lens has.

Adrian
Adrian,

What lens is it? Is it an prime lens? With a prime, the lens in auto (A) position means automatic aperture. The focus may be either manual or automatic depending upon the lens itself.

Then in P mode (camesa P-mode), the aperture is selected automatically when you half-press the shutter release button. If the lens is manual focus, you need then to focus the lens and the gren light in the viewfinder gives you some indication assisting with the focus.

You need also to set the camera Rec mode accordingly to enable the Aperture Ring Auto mode: [using Aperture Ring] = [Permitted] (K-7 instruction manual pages 94 & 294). How is configured your camera?

Hope that it will help ..

Last edited by hcc; 02-08-2010 at 03:06 AM. Reason: Typos
02-08-2010, 03:25 AM   #7
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HI HCC

no its a Vivitar 70-300 manual focus.

My dad gave it to me a littl while back he and mum used to use it on their Pentax ME.

As i said i can use it as a manual lens by using the Aperture ring etc etc, but i was really trying to get it workin as it should using the A aperture setting.

Trouble is im not too sure how it works....im guessing that the A setting connects to a chip inside the lens to set the aperture but what how it works im not sure
02-08-2010, 03:33 AM   #8
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QuoteOriginally posted by milesy Quote
HI HCC

no its a Vivitar 70-300 manual focus.

My dad gave it to me a littl while back he and mum used to use it on their Pentax ME.

As i said i can use it as a manual lens by using the Aperture ring etc etc, but i was really trying to get it workin as it should using the A aperture setting.

Trouble is im not too sure how it works....im guessing that the A setting connects to a chip inside the lens to set the aperture but what how it works im not sure
Nope, no chip inside an A-lens. A-lenses have a series of contacts which transmit max. aperture and also an A-contact that informs the camera, that it is an A lens. If this A-contact does not get contact to the camera (dirt or whatever), tha camera will not recognize the A-lens as such.

Look here: Features and Operation of the Ka Mount

Ben

EDIT: the camera cannot" recognize an A-setting" on the lens - only if the lens is actuially set to A...

02-08-2010, 03:48 AM   #9
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QuoteOriginally posted by milesy Quote
HI Brit

not sure that beginers corner is the right place for this......im trying to get a techincal explanation on how the A setting works (so i can try and repair it)
To some (especially beginners), yes it is quite technical. Questions like this get asked frequently and we put them in Beginners Corner where potentially they will have the most benefit. It also stops the other forums from being clogged with the same questions, which keeps the older members happy.

NOTE: It is a question about a lens so the DSLR forum (where you first posted it) was the wrong forum anyway.

Last edited by Damn Brit; 02-08-2010 at 03:53 AM.
02-08-2010, 04:07 AM   #10
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thanks for the link - thats what i was looking for - now i just need to understand it...

Brit - fair enough
02-08-2010, 06:40 AM   #11
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If you post a picture of the mount somebody here should be able to confirm if there is something visibly wrong with it. If you can turn the aperture ring then it is almost guaranteed that the lens is not actually in "A" mode. The few exceptions to that would be Tamron Adaptall lenses and possibly a few other 3rd party lenses get set to their smallest aperture (f/22, etc) to enable the "A" setting.

Last edited by Steinback; 02-08-2010 at 08:53 AM.
02-08-2010, 06:54 AM   #12
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When the lens is properly set to "A", a pin will protrude from the lens base to engage the recessed contact on the camera mount.

The above image also shows one way to purposely short circuit the A pin (useful for manual lenses.)

Dave

PS sometimes a lens needs to be twisted a bit when mounted for the A pin to properly align for contact.
02-08-2010, 09:46 AM   #13
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Try to gove a read of this too: https://www.pentaxforums.com/forums/pentax-beginners-corner-q/59272-shooting-...x-dslrs-f.html
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