Yes, that too. A lenses move 1 unit per stop (based on area), but pre-A
lenses move only √2/2 (0.7071) per stop (based on diameter) so the images
are progressively overexposed & a correction of about 0.3/stop is needed.
Some degree of manipulation is possible with false coding but re-engineering
the lens innards is the only sure solution. Some fanatics have actually done
just that. I may well have done so too if I was into this 10 years ago.
Alan C
-----Original Message-----
From: P.J. Alling
Sent: Saturday, September 20, 2014 6:35 PM
To: Pentax-Discuss Mail List
Subject: Re: Get with the times (FF DSLR, etc)
It's not that the lenses have to be coded, the aperture is inconsistent
with the movement of the stop down lever in pre A lenses. The original
A lenses just supplied minimum and maximum stop information, coding that
is easy, all that takes is a drill and the proper sized bit, and knowing
where to put a pit on the lens mount, getting the lens to stop down
consistently in accordance with what the camera expects, that's the hard
part.
On 9/20/2014 9:17 AM, Alan C wrote:
When I went digital (only 4 years ago!) I started with a special offer
Canon
1000D body & emf af confirm adaptors for my pentax M42 & K mount lenses.
Set
the desired f on the lens & the camera, open wide to zoom, focus, meter &
lock, then stop down & shoot. It worked very easily with the M42's & their
A/M switch but less easily with the K mounts (with no A/M you have to
count
the clicks) . After a while I found it a pain so I gave the Canon to my
son-in-law & bought a S/H K110D on which AE-L performs the same function
as
the Green Button on later Pentax models. The aperture is stopped down &
the
available light used to determine the exposure. The metering is quite
accurate. M42's with a K-mount adaptor can be used in AV mode if the A/M
switch is set to M but AF confirm only works up to f5.6 (f8 in bright
light). K-mounts would presumably also work like that in AV mode if the
aperture lever was removed. I also tried the "tricking" trick with a strip
of Al foil under the "A" pin on the camera body but, unless the lenses are
coded, the exposures are all over the place. (A lot has been written on
that!) The K7 with a Green Button I now have is similar but the metering
is
less accurate than with the K110D. For me, Sunny 16 is the easiest
solution
& it is good for the brain cells too. However, enough buggering around & I
have decided to get rid of all my pre-"FA" lenses & move with the times.
AF
& AV makes life a hell of a lot easier.
Alan C
-----Original Message----- From: JC OConnell
Sent: Friday, September 19, 2014 10:52 PM
To: Pentax-Discuss Mail List
Subject: Re: Get with the times (FF DSLR, etc)
when I use the green button metering/setting, its only to get me in the
ballpark. I then fine tune
the exposure with either and or both the shutter speed and aperture
setting using the histogram/lcd.
works for me.
jco
On 9/19/2014 4:38 PM, Bruce Walker wrote:
Pentax has definitely failed to promote the Green button. To me it's
just a Mystery Button that I could just as easily cover over with
black electrical tape.
After it got talked about here a few years ago, I made the effort to
read up on it. The manual left me scratching my head, but folks here
insisted it was awesome. I think the issue with the manual is there's
no overview or Big Picture -- why it was added.
When I tried it out, no matter what I did with it it just seemed to
produce random and inscrutable results -- incorrect exposures -- with
no apparent benefit to me.
I think of it as the Do Not Press Me Ever button. It just presents one
more opportunity for me to fsck up the settings if I fumble-finger it.
On Fri, Sep 19, 2014 at 10:08 AM, Darren Addy <pixelsmi...@gmail.com>
wrote:
On Fri, Sep 19, 2014 at 2:54 AM, Alan C <c...@lantic.net> wrote:
If people really want to use pre-"A"
lenses, they can easily work in M mode and use Sunny 16 like we all did
long
ago (& waste no film).
Pentax has actually given us a lot more than that. Most everyone knows
that the Green Button can be set to give you the Program exposure
setting while in Manual. But a lot of people still don't know about
Hyper Manual. Hit the AE/L button after the green button and now you
can change BOTH the aperture and shutter speed (together with only ONE
dial) at your chosen ISO. Super handy.
- - -
Photographers must learn not to be ashamed to have their photographs
look like photographs.
~ Alfred Stieglitz
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