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04-06-2011, 11:52 AM   #1
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SMC Pentax-M lens 'stuck' to largest aperture on K10D

Hi, I have a few m42 lenses for my Pentax Me Super and Pentax K10D. A while ago I bought my first manual with Pentax bayonet, SMC Pentax-M 50mm. It's working just fine on my Pentax Me Super as intended...

But I tested it for the first time on my K10D now... and the aperture is always set to largest 1.7. The aperture ring does nothing and neither does DOF-preview.
What's wrong?

04-06-2011, 12:05 PM   #2
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you need to shoot only in m mode, set your aperture where you want and meter by pressing the green button to get the exposure. In Av mode (or any mode except M) it will meter wide open
there are 2 stickies on using m and k lenses/green button

https://www.pentaxforums.com/forums/pentax-beginners-corner-q/60081-usage-green-button.html

https://www.pentaxforums.com/forums/pentax-beginners-corner-q/110658-using-ma...x-dslrs-f.html
04-06-2011, 12:20 PM   #3
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Hmm, I can't use Av mode as I can on m42 lenses?
But yes, M mode work
04-06-2011, 12:26 PM   #4
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Grease on diaphragm blades

Most likely you have grease on the diaphragm blades. The grease migrates from the focusing helix if the lens gets too hot (don't leave your lens in a hot car). The glass has to be taken out of the lens and the diaphragm blades cleaned. Sometimes you can gently move the diaphragm lever on the lens mount and get the blades to close. If you don't see rust, it is probably grease on evaporated onto the blades. Sometimes you can see shiny areas of grease.

04-06-2011, 12:40 PM   #5
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you can use av mode, but only wide open. i do that when i am shooting low light and will be wide open anyway, like at concerts
04-06-2011, 12:41 PM   #6
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QuoteOriginally posted by pentaxus Quote
Most likely you have grease on the diaphragm blades. The grease migrates from the focusing helix if the lens gets too hot (don't leave your lens in a hot car). The glass has to be taken out of the lens and the diaphragm blades cleaned. Sometimes you can gently move the diaphragm lever on the lens mount and get the blades to close. If you don't see rust, it is probably grease on evaporated onto the blades. Sometimes you can see shiny areas of grease.
Though this could have been the issue i believe he mentioned it worked fine on a film body so it was just an av mode issue
04-06-2011, 12:44 PM   #7
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QuoteOriginally posted by Zakovva Quote
Hmm, I can't use Av mode as I can on m42 lenses?
But yes, M mode work
Unfortunatley you can't use K and M series lenses in Av mode on digital bodies except wide open.
If you want to use the lens at any other f stop than wide open, you need to:
- go to custom menu and enable aperture ring
- use green button metering,

It's PITA as the K10's green button metering is consitently inconsistent, but it can work very well if you know your stuff...
Good luck
09-05-2011, 09:04 PM   #8
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Same problem but on attaching the M len, the apperture opens fully and can't be closed. I have three M lens & it happens with all of them. All lens' work on a P30. I have changed to "Aperture permitted" and use in "M" mode.

Thanks

09-05-2011, 09:40 PM   #9
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That's why the KAF and successor mounts are called 'crippled', because they don't automatically engage the aperture linkage. Write a letter to Pentax. Ask for them to fix this. Right...

I actually find this crippling to be useful with K and M lenses on my K20D. With such lenses, any Auto mode setting (Av, Tv, Sv, TAv) defaults functionally to Av mode. When I mount the M28/2.8 or K50/1.2 or M50/1.7 or M135/3.5, I may set the mode to TAv, which is right next to M on the dial, and set the aperture ring to f/8 or whatever. I can shoot wide-open and let the metering determine the shutter; or if light is bright, I can quickly switch to M, hit the Green button, and take control. Thus I can do a quick-shift between modes -- handy, for street-shooting.

Last edited by RioRico; 09-05-2011 at 10:17 PM.
09-05-2011, 10:50 PM   #10
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QuoteOriginally posted by jibbonpoint Quote
Same problem but on attaching the M len, the apperture opens fully and can't be closed. I have three M lens & it happens with all of them. All lens' work on a P30. I have changed to "Aperture permitted" and use in "M" mode.

Thanks
Do remember that you need to perform "stop-down metering" (using the "green button") before taking a shot.
09-05-2011, 10:56 PM   #11
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Thanks Pio Rico

So, I would need to remove the lever that extends into the camera to operate the aperture ring? Have I got that right?

Hmmm! I'm just wondering if there's something wrong with my Camera. When I fit the lens, the aperture becomes wide open and connot be changed regardless of what I do with the aperture ring.

Last edited by jibbonpoint; 09-05-2011 at 11:11 PM.
09-06-2011, 12:15 AM   #12
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QuoteOriginally posted by jibbonpoint Quote
So, I would need to remove the lever that extends into the camera to operate the aperture ring? Have I got that right?
NO NO NO NO NO!! The crippled mount doesn't AUTOMATICALLY push the lever -- you do that MANUALLY in M mode by pushing the Green button.

First, go into the Custom menu and set Using Aperture Ring to Allowed. Leave it like that for the rest of your life. Now, with the lens mounted, set the aperture ring to f/8 or whatever. Set the mode dial to M(anual), aim at something, and press the Green button. This stops-down the aperture to your setting, and takes a meter reading. You can leave the exposure there, or use the e-dial to adjust the exposure as needed. Now when you hit the shutter, the aperture stops-down to shoot.

QuoteQuote:
Hmmm! I'm just wondering if there's something wrong with my Camera. When I fit the lens, the aperture becomes wide open and connot be changed regardless of what I do with the aperture ring.
That's right, the aperture stays wide-open UNTIL YOU PRESS THE GREEN BUTTON! That's the magic key! Try the procedure I just mentioned and tell us what happens, eh?
09-06-2011, 01:29 AM   #13
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RioRico is right, as always. You can also use depth of field preview on the K10D. Go into 'M' mode, and set your aperture ring onto f8 or whatever. Pull the 'On/Off' switch to the right with your forefinger and you will be able to see the light meter through the viewfinder as the aperture closes. I use my middle finger to adjust the shutter speed and watch the light meter to get the correct exposure. Fiddly, but it works if you have the time.
09-06-2011, 01:44 AM   #14
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Ah! Ha! Thank you very much.

It works. Well, that saved a camera & a lens from some damaging mechanical interference. .

The three lenses I have (+ a 2x tele) are shown with a P30 Camera. I have had these from yesterday when my wife was having a bit of a scavenge (which is how she got me )during our six monthly council cleanup where you throw your rubbish on the footpath & the council pick it up. (Unless my wife gets there first)

The lenses were in their original leather cases except for the Tokina RMC 80-200 which was attached to the camera. The lenes are an M 28 - 2.8 & M 50 - 1.4. I have a couple of M42's (50 1.4 & 135 3.5) and I thought that they would operate the same way.

They are all a bit grubby but I couldn't see any evidence of fungus but I'll have a closer look before I store them with the others.

Interestingly, there were instruction manuals for a Canon Rebel & other Canon peripherals. Someone must have got there first & decided that the Pentax deserved to stay. Lucky me.


Last edited by jibbonpoint; 09-06-2011 at 05:01 AM. Reason: Add more info
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