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01-18-2022, 09:45 AM   #1
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Sigma 500mm f/4.5 mount replacement (Fixed!!!)

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Hi.

I have a Sigma 500mm f/4.5 EX DG APO in Pentax K-mount. The lens mount plate is quite worn, the groove that locks the lens to the camera is almost worn out. Please see attached picture. I have contacted Sigma here in Sweden and they can’t get the part I need. Do any of you have an idea of where I can find one? I belive the part number is 5678P60.

I have tried to replace it with mounts from two other Sigma lenses from the same timeframe, but they do not fit. Thankful for any help.

Best regards, Henrik

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Last edited by henrikknutsson; 01-20-2022 at 01:32 AM. Reason: Fixed
01-18-2022, 10:08 AM   #2
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Have you searched used sites for that lens in "Parts only" condition? You said you tried from other Sigma but were they of similar type? Thinking that other big boy lens from Sigma might have the same part, like this one:

Used Sigma AF 150-500mm f5-6.3 DG HSM APO Lens Pentax in 'Fair' condition
01-18-2022, 10:16 AM   #3
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QuoteOriginally posted by tncowdaddy Quote
Have you searched used sites for that lens in "Parts only" condition? You said you tried from other Sigma but were they of similar type? Thinking that other big boy lens from Sigma might have the same part, like this one:

Used Sigma AF 150-500mm f5-6.3 DG HSM APO Lens Pentax in 'Fair' condition
There are different versions of Sigmas PK mount. The one I need is held in place by three screws and the mount on the 150-500 has four screws.
I tried mounts from a 70-300 and a 10-20, both held in place by three screws but did not fit anyway. Buying a big boy lens even for parts is quite an investment!
01-18-2022, 11:16 AM - 1 Like   #4
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Can't you "mod" the other mounts? Probably just means drilling new holes?

01-18-2022, 12:00 PM   #5
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QuoteOriginally posted by marcusBMG Quote
Can't you "mod" the other mounts? Probably just means drilling new holes?
I have thought of that aswell. If no other solution present itself I will try to modify another mount.
01-18-2022, 12:02 PM - 1 Like   #6
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have a look at the Sigma 170-500. it looks like the screws line up the same as yours. Still not cheap though to get a lens for the mount unless you can find one for parts.
01-18-2022, 01:07 PM - 1 Like   #7
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You could have one made. Not cheap. I think modification of an existing mount plate is a rational approach.

01-18-2022, 01:09 PM - 2 Likes   #8
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QuoteOriginally posted by henrikknutsson Quote
I have thought of that aswell. If no other solution present itself I will try to modify another mount.
If necessary solicit the services of an engineering shop with an accurate drill stand and facilities to do a bit of milling/recessing/countersinking. Use the old mount as a template. Fill in superfluous holes with eg JBweld. that's what I'd do.
01-18-2022, 01:41 PM   #9
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QuoteOriginally posted by marcusBMG Quote
If necessary solicit the services of an engineering shop with an accurate drill stand and facilities to do a bit of milling/recessing/countersinking. Use the old mount as a template. Fill in superfluous holes with eg JBweld. that's what I'd do.
Thanks for the tip!
01-18-2022, 03:25 PM - 1 Like   #10
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QuoteOriginally posted by marcusBMG Quote
If necessary solicit the services of an engineering shop with an accurate drill stand and facilities to do a bit of milling/recessing/countersinking. Use the old mount as a template. Fill in superfluous holes with eg JBweld. that's what I'd do.
Alternatively, a spot of precision brazing to re-fill the damaged mount, then re-drill and re-shape to suit? … obviously remove the mount from the lens first
Good luck
01-18-2022, 10:15 PM - 1 Like   #11
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I don't have an answer for you yet, but I can perhaps help you eliminate possibilities from amid the same era of Sigma manufacturing. I'm measuring these against the mount on my own 500 f/4.5.

EX DC 10-20 f/3.5: 3-screw mount, but the screws aren't in the same location.
EX DC 17-50 f/2.8: 3-screw mount, but screws are in a different location too. Also no screw-drive pass-thru.
EX DG 12-24: 3-screw mount, screws in different location.
EX DG 24-70 f/2.8 HSM: 4 screw mount
EX DG 50 f/1.4: 4 screw mount
EX DG 85 f/1.4: 4 screw mount
EX DG 70-200 f/2.8 HSM II: 3-screw mount, screws in wrong location, no screw-drive pass-thru.
EX DG 50-500 o/s: 4 screw mount

Strangely enough none of the 3-screw mounts even match any of the others, much less the 500mm.
01-18-2022, 10:48 PM   #12
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QuoteOriginally posted by disasterfilm Quote
I don't have an answer for you yet, but I can perhaps help you eliminate possibilities from amid the same era of Sigma manufacturing. I'm measuring these against the mount on my own 500 f/4.5.

EX DC 10-20 f/3.5: 3-screw mount, but the screws aren't in the same location.
EX DC 17-50 f/2.8: 3-screw mount, but screws are in a different location too. Also no screw-drive pass-thru.
EX DG 12-24: 3-screw mount, screws in different location.
EX DG 24-70 f/2.8 HSM: 4 screw mount
EX DG 50 f/1.4: 4 screw mount
EX DG 85 f/1.4: 4 screw mount
EX DG 70-200 f/2.8 HSM II: 3-screw mount, screws in wrong location, no screw-drive pass-thru.
EX DG 50-500 o/s: 4 screw mount

Strangely enough none of the 3-screw mounts even match any of the others, much less the 500mm.
Thanks for eliminating some more lenses for me. I find it strange that they did use the same mount..😅
01-19-2022, 02:52 AM - 1 Like   #13
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QuoteOriginally posted by kypfer Quote
Alternatively, a spot of precision brazing to re-fill the damaged mount, then re-drill and re-shape to suit? … obviously remove the mount from the lens first
Good luck
I think this is a very good option if the op can find a shop to do the work.


Henrik, Does the lens currently attach to the camera okay? What camera do you use it on? Is the camera mount okay .. seems like there maybe some issues with the camera mount if the lens mount looks like that?

Im wondering if for this particular lens it may be best to just have a dedicated body to minimize wear.

Al

---------- Post added 01-19-22 at 03:40 AM ----------

QuoteOriginally posted by Kwong Quote
have a look at the Sigma 170-500. it looks like the screws line up the same as yours. Still not cheap though to get a lens for the mount unless you can find one for parts.

Agree the 170-500 does look like it might work..

Sigma AF 170-500mm f/5-6.3 APO ASP Lens For PENTAX K Mount | eBay

Check out the images.
01-19-2022, 03:42 PM - 1 Like   #14
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Not a lot of help.... But the Mount is the same as the Sigma 300mm/f2.8. I just checked my 500/4.5 and 300/2.8 side by side and they are identical.

That 170-500 does look the same as well. Maybe, buy a doner lens , swap the mounts, and resell the 170-500.. Bit of a risk, and it would devalue the 170-500 considerably.

Only other idea is as I suggested on Pentaxians, to see if you can find a CNC Machine shop or repairer that can drill out the area and pressfitting a sleeve into it, then re-drill the hole.
01-19-2022, 05:46 PM - 1 Like   #15
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Its a stretch but maybe contact the op here...
Sigma 170-500mm APO lens needing repair - PentaxForums.com

If he is a pack rat like I am he may still have this lens.... maybe he can send you it for fair price as a parts lens..just a suggestion.

Al
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