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03-20-2012, 09:33 AM   #1
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K-r is failing to communicate with Sigma lenses. Manufacturers and shops are stumped.

Hi, this is my first post here, but I'm really hoping someone can help me out wwith this.

I have a Pentax k-r, and a Sigma 70-300mm DG Macro, and they aren't communicating with each other. They worked fine together, and had done since last June, up until 10 days ago. When I switch on, I am asked to choose the lens's focal length, I have no apperture control, and auto focus does not work (or attempt to work).

This is where it gets odd. The lens has been sent to the manufacturer, and returned with no fault having been found. It has been tested on a K-10, K-5 and another K-r, and worked perfectly with all of them. The fault is therefore with my K-r body.

Now it gets extra odd. My K-r body has been tested with a number of Pentax lenses, from my 35mm prime, 18-55mm kit lens, and some Pentax zoom lenses (some with a lot of glass, and long zooms). The body has worked with every single one of them, with no problems.

The body has been tested with three Sigma lenses; my 70-300mm, another brand new 70-300mm, and another different Sigma Zoom lens. The K-r failed to communicate with any of them; no focal length recognition, no apperture control, no autofocus.

The problem is with the body, and only affects communication with non-Pentax lenses.

The shop I got the lens in was a fantastic help and spent a long time trying different combinations. The shop I got the body in didn't have any idea. They reccomended I contact Pentax Technical support myself, since if the camera was sent back to the manufacturer, it would be tested with Pentax lenses and no fault would be found.

I have contacted Pentax technical support and the chap on the phone had no idea what was going on, but told me that Pentax would consider the camera functional if I sent it to them. They would only have Pentax lenses to test it with, and they do not guarantee compatibility with third party lenses anyway. My warranty appears to be useless with them. I have insurance on it, but I imagine that will be useless too. They told me to phone their Support Centre, and I am waiting for them to reply to my message. I've still to give Sigma a ring; their invoice actually mentions that they'll retest the lens and my camera. I'm not sure if they could fix a Pentax body, but it will be worth asking them.

Later on I'm going to contact Sigma, but I don't imagine they'll be able to help me since they've already had the lens and couldn't offer any suggestions (and don't deal with Pentax cameras either).

The connections have all been cleaned, the aperture ring is set to Auto, the body is set to auto (neither settings work). Changing aperture ring from prohibited to permission doesn't change anything. The system has been reset, and the newest firmware has been installed.

I'm really in a fix with this. Photography is currently my only means of earning, and I'm already struggling to get work and get by. I can't afford to buy a new camera, and I'd struggle to sell this one when it doesn't work with third party lenses. The nearest Pentax equivilent to my Sigma lens is well out of my price range (which is sitting at 0 if I'm honest). I need to get it fixed.

If anyone can offer any suggestions or experience, I'll really appreciate it. Thanks for taking the time to read through this tale!

03-20-2012, 09:52 AM   #2
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I'll state the obvious have you tried cleaning the contacts on the camera with an eraser end of a pencil?
The problem with 3rd party lenses is they backwards engineer them and some times problems arise when there is a firmware update installed. This is not limited to Pentax all brands come across the problem with 3rd parties occasionally. it definitely sounds like a contact issue.
I would try sending in the camera and lens to Sigma as that has resolved the issue for other people.
03-20-2012, 09:59 AM   #3
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The contacts have all be thouroughly cleaned. The camera and lens used to work with the original firmware, then stopped. Updating the firmware has not changed this.

The lens has already been sent to the maufacturer, and no fault was found (see above).

The problem is that Pentax will probably test the body with a Pentax lens, and find no fault. Pentax do not guarantee against third party compatibility, so I have a feeling that they wont want to do anything.
03-20-2012, 10:15 AM   #4
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No manufacturer guarantees third part compatability unfortunately. and all 3rd parties reverse engineer the system. From what I've read Sigma is usually very good about trying to make it work if they have the body and lens
Given it is a multiple sample issue i think there must be an underlying problem with the body that the sigma presents (it could be a minor variance in the mount placement)
My Sigma 24-70 2.8 has once or twice come up with the flashing aperture and Iafter i make sure it's seated on the a setting on the lens properly i sometimes have to take it off and put it on again (power on and off too)
beyond sending in both pieces to sigma (or to a Pentax authorized depot in case it's a warranty problem with the camera the lens would help diagnose - it is possible this will start happening with Pentax lenses as well after all)
Can't help with who would be best for you in Scotland though

03-20-2012, 10:41 AM   #5
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Same here as eddie, I have a siggy lens that will every once in a while not be contacted correctly with the body, a re-seat of the lens to the body fixes this issue...
03-20-2012, 09:02 PM   #6

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Have you tested with any lens other then Pentax or Sigma?

Just a shot in the dark, but take a stright edge and see if all the contacts on the body are at the same height.

I don't know if the contacts are spring loaded or if it is just a ball and cup design but I would look close at the contacts.
03-21-2012, 06:38 AM   #7
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I don't suppose you did a firmware upgrade between the time your Stigmas worked and when they stopped working?
03-21-2012, 07:05 AM   #8
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something to consider here, is that on some sigma lenses the pattern for the contacts is not on a circle, but is three sets of line segments. I discovered this when I bought an old scrap sigma lens to get a KA mount from it.

Slight misalligmnent of contacts would lead to this problem, especially if the contacts get slightly worn or recessed.

I only have 2 sigma lenses, and neither has had a communication issue, but that does not mean it can't happen/

03-21-2012, 07:34 AM   #9
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Because there is no independent standard for the Pentax mount, any other manufacturer of lenses claimed to fit is responsible for the compatibility. That always involves some risk.
03-21-2012, 07:56 AM   #10
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just as an aside, can you check a few things.

Do you get F-- on the LCD as well. Specifically you cannot select the aperture either?

Also, the prompt for focal lentgh means that the connection issue can be specifically related to the 7th and last pin (furthest away from the lens locking pin) is not connecting. This pin is responsible for focal length and focusing information, the remaining 6 pins are for aperture coding, and the third pin is the "A" pin selecting automatic aperture.

it may be useful to know what functions seem to work and what ones do not, but it could be as simple as either poor connection between the two physical lens mounts, or the 7th pin.

is the mount on this lens plastic for example? this could be of major importance. Also try taking the lens in and out of the A position as this could also impact things if the contact is dirty and since this contact rarely gets used, movement could make it unreliable

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