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09-15-2018, 08:07 AM   #1
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3rd Party lens early K mount - Vivitar 28mm f2.5 67mm fil - can't operate aperture

Hi folks - curly problem for my first post.

I've just received a Vivitar 28mm f2.5 K mount 67mm variant - it matches K14 on this lens db: Great Vivitar 28mm Bestiary: Details

And I'm wondering if anyone else has experience with this lens. It fits and clips into place ok on my K-5iis, but once in place the aperture ring does not operate the aperture. It all works fine off the camera, and works fine on the camera up to a couple of degrees before clicking into place by the locking mechanism.

As received, it already had the excess flange elimination treatment per Flange Fix for Vivitar Lenses - Mark Roberts Photography

It seems there is something just slightly off-spec with the diaphragm control peg position and appears to get either stuck in full-open position once clicked in place... when I try mounting with aperture all the way closed down, mounting the lens opens the aperture.

I've set the shutter to allow firing when no A mode present; everything ok with my M42 lenses. This is my only K mount lens without an A position however. I do have non Pentax K mount and they all seem to have very slight variations, so it seems the tolerance is fairly generous - just somehow this one is past marginal.

I have a couple pictures (hopefully) attached comparing the smc Pentax-A 50mm f1.4 (left) with this Vivitar 28mm (right) - first 2 pics fully stopped down, last pic shows control arm/peg in wide open position.

I hope someone has a tip for this problem.. For the moment, I am looking at trying to secure it in position just before the aperture control starts failing, and trust the friction to keep lens in place - it's usable in this mode, I'm just concerned I might forget and spin it off while focusing.

cheers,
Norbert

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09-15-2018, 08:30 AM   #2
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Every pentax K mount lens has fully open aperture when mounted on the camera. Because the camera should measure exposure with fully open aperture.
Mount the lens on camera. Choose the aperture value on the ring of the lens, check in camera settings to be sure the camera is allowed to use aperture and use green button before shooting to measure exposure. The camera will temporary close the aperture to the selected value you chose on the aperture ring and after that will close aperture during shooting
09-15-2018, 08:45 AM   #3
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QuoteOriginally posted by Medex Quote
Every pentax K mount lens has fully open aperture when mounted on the camera. Because the camera should measure exposure with fully open aperture.
Mount the lens on camera. Choose the aperture value on the ring of the lens, check in camera settings to be sure the camera is allowed to use aperture and use green button before shooting to measure exposure. The camera will temporary close the aperture to the selected value you chose on the aperture ring and after that will close aperture during shooting
Just to add.....you should be in Manual exposure mode.
09-15-2018, 09:00 AM   #4
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The Aperture does not close when mounted to the camera till one of 2 things is done either the green button is pushed for light measurement or you press the shutter release to take the picture. Till then the aperture stays wide open

09-15-2018, 09:08 AM   #5
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There is in the menu that says " using aperture ring " default is disable - make this " enable ".
The camera must be in MF position.
09-15-2018, 10:26 AM - 1 Like   #6
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QuoteOriginally posted by Penview52 Quote
There is in the menu that says " using aperture ring " default is disable - make this " enable ".
The camera must be in MF position.
Are you sure? MF vs AF shouldn't matter. Putting the camera in AF mode with Manual lenses simply enables catch in focus.
09-15-2018, 11:40 AM   #7
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K-mount lenses without "A" contacts need to use stop-down metering in Manual mode. Either by using the green button or (depends on model) optical DOF preview. You can use Av mode but it will only meter and shoot with the lens wide open. You could modify the lens so it always stops down. This is not recommended if you intend on later selling the lens.

Refer to these two threads:
How to use/meter Manual & M42 Lenses on all Pentax DSLRs (K-1, K-3, K-5, K-30, etc) - PentaxForums.com
Manual Metering on Pentax DSLRs with Manual and Automatic Lenses - PentaxForums.com
09-15-2018, 12:13 PM   #8
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" ..Are you sure? MF vs AF shouldn't matter.. "

Try it, MF is the way that the shutter will release even when the aperture is not in " A " settings, except when this lens is restricted on pentax camera.

09-15-2018, 12:54 PM   #9
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QuoteOriginally posted by Penview52 Quote
" ..Are you sure? MF vs AF shouldn't matter.. "

Try it, MF is the way that the shutter will release even when the aperture is not in " A " settings, except when this lens is restricted on pentax camera.
It will release, except focus confirmation has to take place, as focus-priority AF-S is normally engaged, it will also apply to MF operation or to a MF lens.

The aperture ring use in menus is found in the "C" Custom menu #4, I believe. Select "permitted". You can just leave it that way when going back to a regular AF lens, so you don't have to go menus all over again.

Then shoot in M Manual mode on your mode dial, and use the green button to automatically close down aperture and meter as the camera sets shutter speed, after your having manually selected aperture via the aperture ring. There will be no display of aperture, except on the ring itself.

Keep in mind that now the camera is converted mainly to a ye olden manual/aperture priority camera, having centerweighted metering. Your matrix metering automatically switches to centerweighted. This will be displayed. Getting accurate exposure is a little tricky. Try pointing to a brighter area of the scene having some mid-tone color- like well-lit grass (but not too bright like the sky on a sunny day!) to get your metered exposure with the green button, then reposition your camera to get your shot.

If you ever get an old MF common variable-aperture zoom lens to be used in this manner, keep in mind that since you don't have electronic aperture control, only mechanical, as you zoom the aperture value will deviate from what you select on the ring, getting narrower as you zoom to a longer FL, so then you have to re-meter with the green button.

Last edited by mikesbike; 09-15-2018 at 01:30 PM.
09-15-2018, 12:57 PM   #10
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It sounds like the lens is working properly. If you want to check the aperture, with the lens mounted, chose an aperture such as f/16. While looking through the viewfinder, push the DOF lever (on the shutter button on a K5). The viewfinder should go darker as the lens stops down.

Having AF on will enable “catch in focus” if you have it enabled in the menu system. It’s a handy feature.
09-15-2018, 01:03 PM   #11
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QuoteOriginally posted by Penview52 Quote
Try it, MF is the way that the shutter will release even when the aperture is not in " A " settings, except when this lens is restricted on pentax camera.
I am too lazy to open my bags and try it with different bodies and lenses.
But my *istDS with a Petri 2/28 (K-mount, not KA-Mount) was just ready to use.

There was no difference whether the camera was set to AF or MF.

---------- Post added 15-09-18 at 22:09 ----------

QuoteOriginally posted by mikesbike Quote
Then shoot in M Manual mode on your mode dial, and use the green button to automatically meter and the camera sets shutter speed, after your having manually selected aperture via the aperture ring.
Not all Pentax DSLRs use the Green Button, this has changed over time. Earlier series used OK or AE-L button.

EDIT: The *istD series don't even have a Green Button.

Last edited by RKKS08; 09-15-2018 at 01:16 PM. Reason: Typing
09-15-2018, 01:28 PM   #12
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QuoteOriginally posted by Penview52 Quote
" ..Are you sure? MF vs AF shouldn't matter.. "

Try it, MF is the way that the shutter will release even when the aperture is not in " A " settings, except when this lens is restricted on pentax camera.
MF isn't required. AF with M or K series will release when in focus.
09-15-2018, 01:50 PM   #13
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I happen to also have and still use a K-5IIs, so I got it out and modified my post a little to reflect the particular indications of this camera. I also have numerous lenses with aperture rings. I didn't go get an old "M" lens, but just took an AF lens off of "A" to use the ring. But as I remember, they work fine with the camera set to AF, as above.
09-15-2018, 03:07 PM   #14
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When set to AF - this will work if " mike.. said - as focus-priority AF-S is normally engaged" or priority.
If this will not work - again the lens is restricted on pentax camera.

The best is switch MF to AF or vice versa whichever work - and if it will not work - make the lens as a keepsake !
09-15-2018, 09:17 PM   #15
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Brilliant! thanks everyone... pretty sure I haven't even touched the green button since first month six years ago when I flicked through the manual... these manual and vintage lenses I got excited over are giving me both frustration and inspiration... much more fun than just compose and shoot to catch kids events. I've been between P & Av too long, forgot M is for more than just photo-walks :-)

Green button and M mode combo did the trick... I'm happy and comfortable with the purchase, and the education opportunity!
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