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07-30-2018, 11:10 AM   #1
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Repairing DA* 16-50 Broken Zoom

So fun fact, Pentax's zoom mechanism is total garbage in this lens. Its a plastic tab that screws into a metal L bracket for zooming. Well over the weekend my zoom ceased to function on my used Pentax DA* 16-50. Now I am a cheapo and refuse to pay more to repair the lens by sending it in, then attempting to fix it myself. I do not advise anyone not comfortable doing this to take apart your lens. I am a Ricoh tier 2 technician on the Copier side and am fairly mechanically inclined so I figured id give this old lens the one over myself. It is not fully repaired yet, as I need some jbweld but hoping that I can get it fixed soon as I have some gigs coming up that require this lens.


Image 1. Broken bracket that holds the metal L bracket that actually does the zooming

Image 2. Slightly bent and distorted L bracket that zooms the lens. It got bent somehow and was scraping the inside barrel of my lens which most likely attributed to the weakening and eventual breaking of the plastic tab holding it in place.

Image 3. Zoom ring. Be careful removing as there are fingers on the inside that tell the camera what MM zoom you are at. If you damage these, it will not be a great day for you.

Image 4. Moisture inside of the front element. I disassembled everything and was able to dry it out and clean it up properly. Everything is in working order now for the optics anyways. Pending the broken zoom repair.

Image 5. Broken seal that let water into my lens during some rain. Sat between the zoom ring and focus rings. Was another reason I wanted to take the lens apart to get it to dry out better since it condensed on the inside element. Beware of used lenses as you never know what the seals conditions are. These seals are rather weak and small. They break easily.



I have more to come, once I get home. I do not recommend you try this if you are not willing to risk throwing the whole thing into the trash. Honestly, for the cost of repair to send it in, I can buy another online used that will work fine. They can be had for 350.00 all day long and that is why I am not super concerned with botching this repair. So far though, the optics are cleaned and greased back up. Dried out and baked under some UV goodness to kill anything that might try and form before it gets a chance. Now I just need to jbweld this plastic tab back together really good and get the lens reassembled.

The most challenging aspect that I am seeing so far is getting the metal shims back into place. When inserting the optics into the outer shell, you have to be very precise to line up the focus tabs to the metal bars on the optics themselves. Whilst doing this, you must stack 3 shims on either side to be screwed back into place. I have tried inserting them with the shell in place already but have not been very successful in those attempts. Either I get the shell on and miss the focus brackets, or nail the focus brackets and knock the shims out of place. So thats going to be a fun task, on top of trying to screw in the metal L bracket once I make the repair to the plastic tab. It can be done, but just may take many attempts.

I will snag some video to post here as well for everyone to see and document this as best I can. I have not run across many that have taken this lens fully apart as I have, and maybe me being the guinea pig might help someone else in repairing a lens and saving a few bucks. I would prefer to just buy a whole new zoom ring with an intact tab, but I have yet to come across any online for sale, or anyone looking to part out a non functioning 16-50 2.8.

FYI while I have the lens taken apart I do have the optics now sealed in a bag to prevent excess dust from getting in. The area I am working in is already pretty dust free but its no ISO certified clean room either. If a bit of dust scares you inside of your lens, than I advise sending it in for repair and paying the price for such perfection. I personally can live with some dust inside of the outer shell.

This post is for educational purposes only and is not meant to be a definitive guide by any means. I am taking the risk with my equipment for curious minds not willing to do so. So enjoy and stay tuned for updates!

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Last edited by EUPPhotography; 07-30-2018 at 11:18 AM. Reason: Fixed Title
07-30-2018, 11:36 AM - 1 Like   #2
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Are you sure image 5 is a seal and not a band used in some other way? I thought those lenses had a rubber band in them that affected focus or zoom.
07-30-2018, 12:31 PM   #3
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QuoteOriginally posted by UncleVanya Quote
Are you sure image 5 is a seal and not a band used in some other way? I thought those lenses had a rubber band in them that affected focus or zoom.
It was in a standard position for a seal between the zoom ring and focus ring. Several of the other seals are just as thin and flimsy but not broken. I've not heard anything in regards to any bands being used, and this one would be a bit weak imo to be used as one if that were the case. I will investigate further though.
07-30-2018, 12:39 PM - 1 Like   #4
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QuoteOriginally posted by EUPPhotography Quote
It was in a standard position for a seal between the zoom ring and focus ring. Several of the other seals are just as thin and flimsy but not broken. I've not heard anything in regards to any bands being used, and this one would be a bit weak imo to be used as one if that were the case. I will investigate further though.
I'm no expert. I have seen a lens sent to me that didn't focus that I thought the user told me was diagnosed with a broken band in the lens. That may have been an additional issue not the only issue.

07-30-2018, 12:45 PM - 1 Like   #5
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QuoteOriginally posted by EUPPhotography Quote
So fun fact, Pentax's zoom mechanism is total garbage in this lens.
I totally agree with you. Mine did broke five years ago, after 2 years of intense use. Not a PRO grade construction, in my opinion.
I did manage to build a metal index, to replace the plastic tab of the zoom ring, that I screwned in place and are MUCH more stronger now. I'll try to make a pic of one of the prototypes I made.
You have to build very precise, because the space there is very tight, as you saw yourself. But will be basically, another L bracket, so nothing fancy.



QuoteOriginally posted by EUPPhotography Quote
Image 5. Broken seal that let water into my lens during some rain. Sat between the zoom ring and focus rings. Was another reason I wanted to take the lens apart to get it to dry out better since it condensed on the inside element. Beware of used lenses as you never know what the seals conditions are. These seals are rather weak and small. They break easily.
This one is tough. I lost the TWO seals, plus the metal rings that sits with then. Was able to find another seal that fits, but they are much thicker than the original, so the zoom works a little stiffy, but usable. Plus, even if the seal won't work as advertised, still is better than none. I use it a lot in mild rain and have no problem so far.


QuoteOriginally posted by EUPPhotography Quote
The most challenging aspect that I am seeing so far is getting the metal shims back into place. When inserting the optics into the outer shell, you have to be very precise to line up the focus tabs to the metal bars on the optics themselves. Whilst doing this, you must stack 3 shims on either side to be screwed back into place. I have tried inserting them with the shell in place already but have not been very successful in those attempts. Either I get the shell on and miss the focus brackets, or nail the focus brackets and knock the shims out of place. So thats going to be a fun task, on top of trying to screw in the metal L bracket once I make the repair to the plastic tab. It can be done, but just may take many attempts.
This one I can give one tip. Put the lens first. Fit the zoom and focus tabs first, then screw it in place but don't tight then. Let some space. Then, put the shins in their places with a tweezer, sliding in the space you left. It's much easier that way, as you saw yourself, matching the tabs in place is very complicated.

Hope you lens could be back In place soon.

Cheers

Last edited by sungibr; 07-30-2018 at 12:57 PM.
07-30-2018, 01:01 PM   #6
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QuoteOriginally posted by sungibr Quote
I totally agree with you. Mine did broke five years ago, after 2 years of intense use. Not a PRO grade construction, in my opinion.
I did manage to build a metal index, to replace the plastic tab of the zoom ring, that I screwned in place and are MUCH more stronger now. I'll try to make a pic of one of the prototypes I made.
You have to build very precise, because the space there is very tight, as you saw yourself. But will be basically, another L bracket, so nothing fancy.





This one is tough. I lost the TWO seals, plus the metal rings that sits with then. Was able to find another seal that fits, but they are much thicker than the original, so the zoom works a little stiffy, but usable. Plus, even if the seal won't work as advertised, still is better than none. I use it a lot in mild rain and have no problem so far.




This one I can give one tip. Put the lens first. Fit the zoom and focus tabs first, then screw it in place but don't tight then. Let some space. Then, put the shins in their places with a tweezer, sliding in the space you left. It's much easier that way, as you saw yourself, matching the tabs in place is very complicated.

Hope you lens could be back In place soon.

Cheers
Yeah, I tried not tightening the screws to get the shims in place but for some reason they just don't want to go in. Granted that was at 3am this morning and I didn't have the patience to really deal with it all that much. I will be giving it another go when I get home. The metal bracket you built does sound intriguing though. I really would be curious to see what you did for that. I am not at all confident that the jbweld is going to hold up to the test of time, and an all metal construction of that part does indeed intrigue me. I will be placing the seal back on, even though it is broken, but it just amazed me at how thin and flimsy they were. I expected a lens of this caliper to be better constructed. I was sorely disappointed upon disassembly to see just how cheaply Pentax went on the internals. The glass is great, but the outer barrel and internal parts for zooming and focusing are extremely lack luster. I will be taking better pics with my camera since I have a 50-135 as well to document everything nicely for those in the future. Right now I just had some cell phone shots to upload, but will get right proper with the images here tonight. Figure I have it apart, I might as well document it as well as I can since I can't find many out there that have.
07-30-2018, 01:10 PM - 1 Like   #7
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QuoteOriginally posted by EUPPhotography Quote
I will be placing the seal back on, even though it is broken, but it just amazed me at how thin and flimsy they were. .
Again, totally agree with you. They are way to fragile.
But I don't recomend put then back in the final assembly. They will jam the rings. I know. Happened with me. TWICE .
I'm in work now, but will try to find the prototype I made. I guess I still have it. I would snap a pic from the one on the lens, but I disassembled and reassembled the lens so many times that I'm afraid I couldn't put it together once more
07-30-2018, 01:16 PM   #8
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QuoteOriginally posted by UncleVanya Quote
I'm no expert. I have seen a lens sent to me that didn't focus that I thought the user told me was diagnosed with a broken band in the lens. That may have been an additional issue not the only issue.
Thanks. I will look into it just to make sure. I appreciate the info

07-30-2018, 03:40 PM   #9
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I had the same zoom issue in one of mine. I resorted to using glue to reinforce the L bracket and it seemed to work well. It's an extremely stupid design on a premium lens.
07-30-2018, 08:02 PM   #10
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QuoteOriginally posted by EUPPhotography Quote
I am taking the risk with my equipment for curious minds not willing to do so. So enjoy and stay tuned for updates!
Thanks greatly for the info and photos. I will not be trying a repair. My 16-50 zoom did freeze and I paid about $280 for the repair, which took just under 3 mos. total time. I have been curious about doing a lens repair, however. Some of the simpler, older lenses with fungus - I wonder if they would be easier.
07-30-2018, 08:45 PM   #11
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This is the first try form the metal tab I made

Heres two pics of the first one I tried.
This one is very rough and the first one I made. The definitive one inside the lens is a much better build, but I hope you can get some base to work with


The curved side is the side you screw inside the zoom ring and in the exact same place of the plastic tab.
The flat side is the tab that will be screwned in the L tab that connects the zoom group.
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07-30-2018, 10:31 PM   #12
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QuoteOriginally posted by EUPPhotography Quote
It was in a standard position for a seal between the zoom ring and focus ring. Several of the other seals are just as thin and flimsy but not broken. I've not heard anything in regards to any bands being used, and this one would be a bit weak imo to be used as one if that were the case. I will investigate further though.
I would expect that the bands are pretty cheap and potentially fragile on being removed, such that official repair service would just replace all of them when putting a lens back together.
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