[jamesm007]

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My oldest lens is my Sigma 17-70mm f/2.8-4.5. Lately I have noticed a lot of posts saying the Sigma lens is not communicating with their camera. Sometimes the lens worked with the older camera such as my K20D but when put on the K5 or newer model it would ask for the focal length or other strange behavior.Most people say clean the contacts. That is logical and right. I had an ordeal with my Sigma 17-70mm f/2.8-4.5 to. Its in this thread started by someone else.Look for the big post with pics (of course).



https://www.pentaxforums.com/forums/general-technical-troubleshooting/233841-k5-sigma-17-70-a.html



During all this time I have noted for a long time a discoloration of my lens mount. I did not know what to think. So I just ignored it. The blue arrow below points to it. This pic taken with the kit lens and a K5 with flash had its color and other parameters increased for maximum contrast of the stain inPP.









This pic is a out of camera jpeg no PP to show how it looks in real life. Its still very noticeable.







Now the moment. Just today reading a review at ehotozine of the new Sigma 17-70mm f/2.8-4.0 (C model)I found its mount is made of brass “This lens weighs around 465g, which is reasonably lightweight. Despite not being heavy the build quality is very good, and the lens mount is made of brass ”.OK, now I understand the discoloration. Sigma probably has been using brass even in its older 17-70mm f/2.8-4.5, and other lens. I now understand why the Sigma works better on the K20. Brass is a soft metal compared to stainless steel from what I read. With years of use and sitting on my K10D then K20D its pretty much shaped to the K20D and hence no problems. With the new K5 problems!



IMO - There is distortion someplace. I am not sure and won’t try to guess. But its creating a contact with the data pins that’s not tight enough. So add in slightly bad contacts, that have lost some of their conductivity over the years and you have problems. A good cleaning bringing the contacts back to 100% conductivity can fix it most of the time I guess, but am not sure. It worked for me though. I know of one person who’s problem was with wear and tear on the flex cable.



My next oldest lens and only a few months newer than the Sigam is my Pentax DA55-300mm. It has never had a mount or communication problem. I don’t know what the mount is made of but I do know only the Sigma17-70mm is showing this discoloration. I also own a Sigma 10-20mm (its older as well) I don’t seem to see any discoloration with any of my other lens (Perhaps just a tiny bit - perhaps not). The cleanest most color consistent mounts is my old Pentax M 50mm f/2 and Ricoh M 50mm f/1.7 go figure!

Now cleaning it?

[jamesm007]

My oldest lens is my Sigma 17-70mm f/2.8-4.5. Lately I have noticed a lot of posts saying the Sigma lens is not communicating with their camera. Sometimes the lens worked with the older camera such as my K20D but when put on the K5 or newer model it would ask for the focal length or other strange behavior.Most people say clean the contacts. That is logical and right. I had an ordeal with my Sigma 17-70mm f/2.8-4.5 to. Its in this thread started by someone else.Look for the big post with pics (of course).



https://www.pentaxforums.com/forums/general-technical-troubleshooting/233841-k5-sigma-17-70-a.html



During all this time I have noted for a long time a discoloration of my lens mount. I did not know what to think. So I just ignored it. The blue arrow below points to it. This pic taken with the kit lens and a K5 with flash had its color and other parameters increased for maximum contrast of the stain inPP.









This pic is a out of camera jpeg no PP to show how it looks in real life. Its still very noticeable.







Now the moment. Just today reading a review at ehotozine of the new Sigma 17-70mm f/2.8-4.0 (C model)I found its mount is made of brass “This lens weighs around 465g, which is reasonably lightweight. Despite not being heavy the build quality is very good, and the lens mount is made of brass ”.OK, now I understand the discoloration. Sigma probably has been using brass even in its older 17-70mm f/2.8-4.5, and other lens. I now understand why the Sigma works better on the K20. Brass is a soft metal compared to stainless steel from what I read. With years of use and sitting on my K10D then K20D its pretty much shaped to the K20D and hence no problems. With the new K5 problems!



IMO - There is distortion someplace. I am not sure and won’t try to guess. But its creating a contact with the data pins that’s not tight enough. So add in slightly bad contacts, that have lost some of their conductivity over the years and you have problems. A good cleaning bringing the contacts back to 100% conductivity can fix it most of the time I guess, but am not sure. It worked for me though. I know of one person who’s problem was with wear and tear on the flex cable.



My next oldest lens and only a few months newer than the Sigam is my Pentax DA55-300mm. It has never had a mount or communication problem. I don’t know what the mount is made of but I do know only the Sigma17-70mm is showing this discoloration. I also own a Sigma 10-20mm (its older as well) I don’t seem to see any discoloration with any of my other lens (Perhaps just a tiny bit - perhaps not). The cleanest most color consistent mounts is my old Pentax M 50mm f/2 and Ricoh M 50mm f/1.7 go figure!

Now cleaning it?

Well a day latter and a bunch of tries trying to clean the mount and some reading has me thinking this is not discoloration, this is wear! The brass is coated. I tried a magnet on all my lens. The magnet sticks strongest to the Sigma 17-70mm, hardly to any Pentax mount and the least to Sigma 10-20mm. Its not a sure test however. Brass has some good traits. I found putting a new lens mount on a camera is a standard thing. With time they wear down. Could it be my K20D mount is worn down giving better contact to the lens data pins versus the new K5? Could be. But I am guessing right now. There are too many variables for me to make any conclusions.
Other than this. When confronted with a lens to body communication problem don't forget to take into account wear on the lens and or body mount. They play a role.

[Tayfun]

I have the same communication problem with my Sigma 70-300 on my K5. But no problem on my K7 or Mz-5n. So I guess there is a problem by K5 - Sigma communication

[entropy1]

I just got a Sigma 50mm f/2.8 macro lens off ebay and it's not recognized electrically at all by my K30. I no longer have another Pentax body to test it on, but trying to clean the contacts with an eraser did no good. I was thinking at first it was just the problem a number have reported with the A setting on the aperture ring not working, but realized that the lens isn't communicating at all - I have to tell the camera the focal length and manually set f-stops don't get communicated, either. I'd love to hear of a solution. I wonder if the K30 and the K5 use the same mount and have some issue. Well, thank goodness for the green button! On a prime macro lens, this is an annoyance, but not a big deal.

[lister6520]

Have you tried cleaning the contacts with a glass fibre brush rather than the pencil eraser? Something like this:
3pc Scratch Brush Set Retractable Fibre Glass Stainless Steel Brass Cleaning | eBay

Also something else you might try is to insert some thin pieces of aluminium foil between the lens flange and the camera to make it fit tighter. Make sure thoug that you don't short out any contacts or put the foil over the screw drive. Not a great solution but might be worth it if it works and you don't change the lens often. I

I have two Sigma lenses, 50mm F1.4 and 150-500. Both of them fit a little loose to the mount so with wear I would not be surprised if they become too loose to guarantee good contact.

[stevebrot]

I just got a Sigma 50mm f/2.8 macro lens off ebay

Before you start scouring your lens, is the aperture ring set and locked in the "A" position? This should allow for all exposure modes and should result in the aperture being displayed in the rear LCD rather than just F----. If you have a continuity tester (ohmmeter) you should be able to test the "A" contact against the mount face. For some lenses there is a pin that retracts when the ring is off the "A" position. For others there is an internal switch that breaks the circuit.

Next question...Is your Sigma an AF lens? If not, the lens will not provide focal length or lens code information or any other information beyond maximum/minimum aperture and whether the ring is in the "A" position. The data pin is only present and active for AF lenses.

In regards to cleaning, a pencil eraser can be used as can a paper towel sparingly moistened with rubbing alcohol. There should be no need to scour or abrade the surface since most mounts are stainless steel or chrome-plated brass and the contacts are made of a similar conductive material. There should be no need to short the contacts with foil. If the mount is too lax due to wear to allow for consistent electrical contact with the body, I would contact the seller and request a refund.

Guide to lens mount pins:

http://kmp.bdimitrov.de/technology/K-mount/Ka.html


Steve

[Lowell Goudge]

Actually, if you look at the photo of the mount, you may see the ral problem.

I noticed this a long time ago, where the contact pins on sigma lenses are not on a perfect circle, but in 3 line segments, they are close but into perfect.

The "defect" you show is called grassing, you have mountd and uncounted the lens enough to wear off the Crome to expose the brass base metal of the mount

[stevebrot]

but in 3 line segments,

I won't say that what you are claiming isn't so, but a careful look at the bottom photo shows the score lines from the body cleanly intersecting each of the contacts.

The most recent question was in regards to a Sigma 50/2.8 Macro lens that is identified by the camera as a non-A lens. Until we get a little more information, I think it is premature to be assigning a cause.

• Is this an A-contact lens? If not, case closed.
• Is the aperture ring locked onto the "A" position?
• Is there continuity between the mount face and "A" contact when in the "A" position? (Confirm that internal switch works)

Only when the above have been addressed are we in a position to put the blame on the lens/body connection. Assuming, of course, that the body is working properly. For what its worth, "A" contact problems are a known issue with some of the older, non-AF Sigma 50/2.8 macro in the lens database:

https://www.pentaxforums.com/userreviews/sigma-50mm-f2-8-macro.html


Steve