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09-11-2013, 05:43 AM   #1
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sigma mini-wide11 2.8 28mm won't work on my k-5

Hello everyone iv just purchased a couple of old lens a sigma mini-wide 11 2.8 28mm and a sigma uc zoom 70-210mm 4-4.5 but I can't get them 2 work on my k-5 when I attach them 2 my camera, i tried the sigma 28mm2.8 first and its asking for the focal length is this right the lens ring is in the A position but still asking for focal length,, but even when I put the focal length in the f number won't go under 4.0 am getting similar results with the sigma uc zoom 70-210 4-4.5 , the lad I got them of said he used them on hes pentax film camera, thanks everybody in advance

09-11-2013, 05:46 AM   #2
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Try cleaning the contacts on the lens.
09-11-2013, 06:21 AM   #3
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Why would you want the focal length to go under 4.0. A 28 MM lens has a focal length of 28. As previous poster has said - give the contacts on the lens a clean.
09-11-2013, 06:25 AM   #4
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I have the sigma mini wide as well and it worked fine with my Pentax digital cameras. You have to input the focal length because the lens is not chipped to give the focal length to the camera. Have you checked custom settings to enable camera operation when the aperture ring is not in the "A" position as well? Can't think of why you can't change the aperture via the camera below 4.0. do you have depth priority set on your camera?

09-11-2013, 06:43 AM   #5
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There both look very clean both lens are doing the same thing what can I clean them with thanks
09-11-2013, 07:20 AM - 2 Likes   #6
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Take a look at this page:

Features and Operation of the Ka Mount

The contacts on your lens give the camera a binary code to signify what the lens' aperture range is. Each contact is one digit: a plastic (insulated) contact is a 0, and a metal (conductive) contact is a 1.

The code your lens is supposed to make is 011*10, where the * is the contact that tells the camera it's an auto-aperture lens. That code means f/2.8-f/22. The code your camera is getting is 001*10, which means f/4-f/22. The metal contact which is second from the bottom is not making contact, so the camera thinks it's an insulator, or a 0. It's either dirty or too far recessed to make contact. If cleaning it (use rubbing alcohol and a cloth) doesn't work, try putting a little piece of metal foil over it.
09-11-2013, 07:21 AM   #7
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QuoteOriginally posted by safc Quote
There both look very clean both lens are doing the same thing what can I clean them with thanks
I would try a bit of isopropyl alcohol on a cotton swab or some lens cleaning solution. You can also use an eraser, not a pencil eraser but something like a Pink Pearl eraser.
09-11-2013, 07:40 AM   #8
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QuoteOriginally posted by kev.pride Quote
Why would you want the focal length to go under 4.0. A 28 MM lens has a focal length of 28. As previous poster has said - give the contacts on the lens a clean.
Iv put the focal length in at 28 with this lens being a 28mm focal length, am I right the f number on the right side on the screen should go down to 2.8? But its only going down to 4.0, the camera in M mode how do I put (depth priority in my camera thanks)

09-11-2013, 08:27 AM   #9
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QuoteOriginally posted by scratchpaddy Quote
Take a look at this page:

Features and Operation of the Ka Mount

The contacts on your lens give the camera a binary code to signify what the lens' aperture range is. Each contact is one digit: a plastic (insulated) contact is a 0, and a metal (conductive) contact is a 1.

The code your lens is supposed to make is 011*10, where the * is the contact that tells the camera it's an auto-aperture lens. That code means f/2.8-f/22. The code your camera is getting is 001*10, which means f/4-f/22. The metal contact which is second from the bottom is not making contact, so the camera thinks it's an insulator, or a 0. It's either dirty or too far recessed to make contact. If cleaning it (use rubbing alcohol and a cloth) doesn't work, try putting a little piece of metal foil over it.
Cheers for all your help I really appreciate everything,am going 2 buy some lens cleaning solution
09-11-2013, 09:34 AM   #10
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One last thing please has anybody got a diagram of the back of the sigma wide11 just 2 see whitch 1 that needs cleaning thanks once again for all your help

Last edited by safc; 09-11-2013 at 10:16 AM.
09-11-2013, 09:55 AM   #11
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The sigma lenses of this era are often fiddly this way -- piece of foil tape in the right place can fix it. My super-wide II used to the same thing -- would read f/2.8 on a cold day and f/4 if it warmed up (supposed to be f/2.8). Foil tape to keep the contact contacting, and it works fine.
09-11-2013, 10:48 AM   #12
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QuoteOriginally posted by vonBaloney Quote
The sigma lenses of this era are often fiddly this way -- piece of foil tape in the right place can fix it. My super-wide II used to the same thing -- would read f/2.8 on a cold day and f/4 if it warmed up (supposed to be f/2.8). Foil tape to keep the contact contacting, and it works fine.
Do u just put the foil tape over all the terminals cheers
09-11-2013, 10:51 AM   #13
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No, just a little piece in the right place...gotta follow the chart. Let me check my lens...
09-11-2013, 11:28 AM   #14
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QuoteOriginally posted by vonBaloney Quote
No, just a little piece in the right place...gotta follow the chart. Let me check my lens...
I thought that but was unsure cheers for ya help
09-11-2013, 11:50 AM   #15
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A couple of notes.

What causes the reported "fiddly" behaviour is the fact that the contact pins on some sigma A lenses are drilled in a pair of straight lines of 3 pins, lying tangent on the true circle center of the Pentax mount. This causes minor mis allignment of some pins and lost contact. Rock the lens back and forth in the locked position and see if you can get F2.8

Second, the mini wide II with KA mount suffers very badly from lateral CA. Unless you plan to spend time in PP with every image and correction the edge resolution is pittifull at best
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