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06-28-2012, 03:08 AM   #1
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Green button and AE-L button

Hi Guys

I revisited this article/page Shooting manual lenses on Pentax DSLRs « robertsdonovan.com which is good info for beginners. Towards the end of this article where it says 'Here's how it works....', it is advised that you set the f-stop, iso, focus, compose and then press the green button to get a suitable shutter speed.
I am using K-x with an M 28/2.8 lens on AV mode and manual focus. Green button settings are on 'P-line' and the e-dial settings are 'off'.
The shutter speed doesn't change after pressing the green button if I follow the steps from that article/page. Also no matter where my aperture ring lies (2.8 or 22) I get the same shutter speed after I half-press the shutter, meaning its sitting on the same f-stop all the time (which f-stop I don't know, by the way is there a way to know that when using manual lenses via LCD display?).
There must be some way to get the K-x to adhere to the f-stop I want to shoot in in AV mode. Also, why doesn't the green button work according to what's mentioned in the article/page? Are my green button settings for this purpose right?
Thanks.

06-28-2012, 03:17 AM   #2
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Switch to M, and green button should be TV shift.

QuoteOriginally posted by voyager13 Quote
There must be some way to get the K-x to adhere to the f-stop I want to shoot in in AV mode.
No, there isn't. The lens has to have an 'A' on the aperture ring, and then set the aperture on the body. Your lens is an M type, so it will only work wide open in Av, or stopped down in M mode. For more information google "pentax crippled mount".

Last edited by kcobain1992; 06-28-2012 at 03:23 AM.
06-28-2012, 03:50 AM   #3
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QuoteOriginally posted by kcobain1992 Quote
The lens has to have an 'A' on the aperture ring, and then set the aperture on the body. Your lens is an M type, so it will only work wide open in Av, or stopped down in M mode.
Doesn't that mean that the green button won't determine shutter speed in manual (non-A) lenses like the M and K's unless I am in Manual mode?
Yes as you mentioned it allowed me to set the f-stop on my A zoom lens.
What use can the green button (and the AE-L button as well) be when using M and K lenses or are they mainly useful when non-M/K lenses are used?
06-28-2012, 04:00 AM   #4
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QuoteOriginally posted by voyager13 Quote
Doesn't that mean that the green button won't determine shutter speed in manual (non-A) lenses like the M and K's unless I am in Manual mode?
Yes, that is true. However, in M mode, the green button gives a proper exposure regardless of the lens used (it can be used even with modern lenses). It is only especially useful with M and K series.

QuoteOriginally posted by voyager13 Quote
Doesn't that mean that the green button won't determine shutter speed in manual (non-A) lenses like the M and K's unless I am in Manual mode?
Yes as you mentioned it allowed me to set the f-stop on my A zoom lens.
What use can the green button (and the AE-L button as well) be when using M and K lenses or are they mainly useful when non-M/K lenses are used?
My only use of the AE-L button is when I want to lock exposure during video. The green button can also be set to act as optical preview - as long as you keep it pressed, the lens is stopped down at your desired aperture and there is a meter in the viewfinder that tells you if you are over- or underexposed. The AV +/- button also acts like a green button with M/K/M42, so you can have the quick exposure adjustment too.

06-28-2012, 04:50 AM   #5
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aperture lever

Without the green button, the aperture is wide-open all the time because of the aperture lever near the base of the lens. If you have an old tamron adaptall-2 adapter that you are willing to destroy, you can bend off sideways the aperture lever near the base of the adapter - when you mount it to the lens and then the lens to the camera, the aperture will be free to stop down manually. Of course, at f/8 and beyond it becomes extremely dark, but it illustrates the difference in using a lens without that lever. Would not advise this on a fixed lens, kills the resale value. The green button magically holds that aperture lever to the right point you set on the lens aperture, similar to a depth of field preview, but with Tv changed in the info line. The technique with the adaptall-2 mount is useful with still life and macro photography where I focus at full brightness, then stop down manually to take the shot. Hope that helps.

06-28-2012, 04:57 AM   #6
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QuoteOriginally posted by goldenarrow Quote
Without the green button, the aperture is wide-open all the time because of the aperture lever near the base of the lens. If you have an old tamron adaptall-2 adapter that you are willing to destroy, you can bend off sideways the aperture lever near the base of the adapter - when you mount it to the lens and then the lens to the camera, the aperture will be free to stop down manually. Of course, at f/8 and beyond it becomes extremely dark, but it illustrates the difference in using a lens without that lever. Would not advise this on a fixed lens, kills the resale value. The green button magically holds that aperture lever to the right point you set on the lens aperture, similar to a depth of field preview, but with Tv changed in the info line. The technique with the adaptall-2 mount is useful with still life and macro photography where I focus at full brightness, then stop down manually to take the shot. Hope that helps.

Easier really to do with an M42 lens, no destruction implied either.
06-28-2012, 10:30 AM   #7
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AE-L can be useful for shooting panoramas too (though not in Manual, obviously...).
06-28-2012, 12:26 PM   #8
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I use the +/- button instead on K-x but most times I tweak the shutter speed. See my post and many responses "Using M lens". Maybe that will help.

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