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12-01-2012, 05:19 AM   #16
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Thx Tom, it has a point ! I'll try and let you know.

12-01-2012, 06:34 AM   #17
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QuoteOriginally posted by TomB_tx Quote
The lens also will not stop down if the camera doesn't detect that a lens is in place. If you try the "preview" lever without a lens in place nothing happens. The lens mount must be clean and conductive so that the electrical contacts can tell it is mounted. Some 3rd party lenses have anodized mounts that don't make electrical contact. Some people report "sandpapering" the back of the lens where it meets the electrical contacts to correct this problem, and others have tried a piece of foil over the contacts. Both methods report success - that the lens will then stop down.
Yes...of course! We all seem to have forgot!

Here's an example of surgery needed with my Cosina 35mm f/2.8 Cosinon W. This modification is also mandatory for focus confirmation and Cath-in-Focus to work:
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12-01-2012, 11:20 AM   #18
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Great !!! Thank you all ! especially TomB_tx! I've refined it with a sandpaper and everything now works great ! Great advice !

Adam, maybe it would be usefull to mention this in your post here https://www.pentaxforums.com/forums/pentax-lens-articles/110657-how-use-meter...k-x-k-7-a.html. Like I said, I read many articles about shooting with these old Pentax K lenses, but nobody never mentioned this one !

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12-01-2012, 11:48 AM   #19
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Good to hear the problem is solved . I have a Vivitar 135 (Cosina-built) with an anodized mount as shown in the photos. However, it works fine other than lacking focus confirmation & CIF. I've just gotten used to working around its limitations, but I might try a bit of sandpaper as well!

12-01-2012, 03:17 PM   #20
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QuoteOriginally posted by TomB_tx Quote
The lens also will not stop down if the camera doesn't detect that a lens is in place. If you try the "preview" lever without a lens in place nothing happens. The lens mount must be clean and conductive so that the electrical contacts can tell it is mounted. Some 3rd party lenses have anodized mounts that don't make electrical contact. Some people report "sandpapering" the back of the lens where it meets the electrical contacts to correct this problem, and others have tried a piece of foil over the contacts. Both methods report success - that the lens will then stop down.
Without a lens in place the lever actuates on my K10D when the preview is actuated. Must be something they changed in later bodies.
12-06-2012, 08:14 AM   #21
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QuoteOriginally posted by Not a Number Quote
Without a lens in place the lever actuates on my K10D when the preview is actuated. Must be something they changed in later bodies.
This was probably decided in a meeting with the topic, "How can we further cripple the K mount?"
12-07-2012, 03:07 AM   #22
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QuoteOriginally posted by Not a Number Quote
Without a lens in place the lever actuates on my K10D when the preview is actuated. Must be something they changed in later bodies.
I believe this was changed for the camera to be able to change aperture in video without having to open aperture fully between each change.

I like the feature that the camera check for aperture lever on start-up, so it don't have to move the lever if using non K-mount lenses. Makes the camera a bit quieter when using m42 lenses.
12-10-2012, 04:17 AM   #23
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Not sure whee Pentax made the change, but painted mounts became an issue with me on the K7. It was discussed at length with respect to extension tubes and being unable to stop the lens down if it was on a painted extension tube.

02-26-2013, 06:42 PM   #24
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Very useful info. I bought a Pentax camera recently and wanting to use my old manual lenses. 2 out of 3 work without any problems. The standard lens doesn't stop-down during metering and I thought I have some setup problems. After long searching, I found this website and gives me the exact solution I need.

Now all 3 lenses are working on my DSLR. Very happy.
11-20-2013, 06:02 PM   #25
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QuoteOriginally posted by Stone G. Quote
Yes...of course! We all seem to have forgot!

Here's an example of surgery needed with my Cosina 35mm f/2.8 Cosinon W. This modification is also mandatory for focus confirmation and Cath-in-Focus to work:
Hi. May I know what grit of sand paper works? I've tried 1200 and 1200 but they don't seem to work.. foo fine maybe. Thanks.
11-20-2013, 06:45 PM   #26
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QuoteOriginally posted by el baroda Quote
Hi. May I know what grit of sand paper works? I've tried 1200 and 1200 but they don't seem to work.. foo fine maybe. Thanks.
You need to go to bare metal.


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11-20-2013, 07:20 PM   #27
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QuoteOriginally posted by stevebrot Quote
You need to go to bare metal.


Steve
Hi Steve. This is what I am doing at the very moment using P360 silicon carbide sandpaper. A really tedious job but I can see the bare metal now. Hopefully, I can test the lens tomorrow and post photos. Thanks and regards.
11-21-2013, 02:24 AM   #28
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QuoteOriginally posted by el baroda Quote
Hi. May I know what grit of sand paper works? I've tried 1200 and 1200 but they don't seem to work.. foo fine maybe. Thanks.
Well, I cannot remember the grade, but it was VERY coarse, and here's the reason why:

'Anodizing' isn't just like painting the aluminium surface. It's a process in which the surfaxe is oxidized and dyed to make a structure like this:



Source: Electronic Thingks - Anodising guide - 1. What is "anodising"?

So, it takes not only coarse sand paper, it also takes some time and 'brute force', as you have discovered.......
11-21-2013, 11:17 AM   #29
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QuoteOriginally posted by TomB_tx Quote
The lens also will not stop down if the camera doesn't detect that a lens is in place. If you try the "preview" lever without a lens in place nothing happens. The lens mount must be clean and conductive so that the electrical contacts can tell it is mounted. Some 3rd party lenses have anodized mounts that don't make electrical contact. Some people report "sandpapering" the back of the lens where it meets the electrical contacts to correct this problem, and others have tried a piece of foil over the contacts. Both methods report success - that the lens will then stop down.
To add my penny's worth: this problem is specific to K5, K30 and (my) K-r etc. Without an electrical contact, specifically to the 7th data contact at the half past position, the lens won't stop down and the green button won't work (nor will catch-in focus). It does not occur with K10D, K20D... (= my samsung GX20), the latter will operate eg green button even with no lens mounted. This issue is also commented on here albeit slightly different context
Jessops Auto Extension Tubes PK-A reviews - Pentax Camera Accessory Review Database

I used a dremel bit by hand to take off the anodising and get the 7th contact to connect
11-22-2013, 01:13 AM   #30
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QuoteOriginally posted by Stone G. Quote
Well, I cannot remember the grade, but it was VERY coarse, and here's the reason why:

'Anodizing' isn't just like painting the aluminium surface. It's a process in which the surfaxe is oxidized and dyed to make a structure like this:



Source: Electronic Thingks - Anodising guide - 1. What is "anodising"?

So, it takes not only coarse sand paper, it also takes some time and 'brute force', as you have discovered.......
Thanks for explaining what the problem is. I am at work tonight. I will spend the entire shift trying to remove as much of the top layer as possible. I tried the foil option again this afternoon making sure all the contact points on my camera were fully covered. The result is quite promising. Now, I am sure nothing's wrong with the lens itself. Best regards.
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