The Sigma 50-500mm f4-6.3 EX APO RF HSM is a pretty decent lens for the money. It provides a reach that is generally inexpressible without a huge investment of 5 to 10 times it's cost in equipment. Recently, it was necessary to repair one. The issue was a malfunctioning focus. Manual and auto both were being impeded at their far range. It was rather maddening because, first it worked, then it didn't, then it did, then it didn't. I wasn't about to invest any money in this lens, so, I decided to fix it myself. At least, I was going to give it the old college try.
I think I spent more time looking at this lens, trying to figure which screw to pull first and next than actual repair. It was a tricky little devil to start out. It's also maddening how little information is available for doing such work. Nothing on the web for free or for sale. You would think some industrious souls would be selling schematics or manuals but I guess maybe the manufacturers probably don't want that sort of thing getting around.
So here's a couple photos of the process. Fortunately, I didn't have to go too far into this puppy to figure out the problem and fix it.
First up is a shot of the mounting plate. It's straight forward enough to remove the obvious screws, but that's not the way. In the sides of the vertically oriented sections of the mounting flange are itty (and I do mean itty) bitty screws. You can probably see the the black piece in the center which is obviously disjointed. There are four screws. Two hold the round piece and two hold the contact plate in place. Remove them all.
Once that's done then remove the mounting flange retaining screws. That will allow the aperture selection ring to come loose. Remove it and note that there are some (5 in my case) shims underneath it. I'm not sure if sorting order of the shims is important, but keep them in order just in case. They are flimsy and will interweave with each other if you don't keep them tidy and in order. There will also be a long metal arm which works the iris of the aperture. Be sure to note that it has to be reinstalled into a slot down inside the barrel.
Now you have exposed the entire circuit board and you will notice there are three screw heads visible in the outer most diameter. These are the next to be removed and will facilitate the removal of the upper most part of the lens barrell.
A note about screws in general, and specifically, about screws within a lens. You MUST BE EXTREMELY DILIGENT when attempting to loosen and tighten these screws. It it more than likely that they have had a thread locking compound applied and are GLUED in place. Further, it is imperative that you use the appropriate driver bit. There are many different sizes, and use of an inappropriate driver bit will result in a stripped head. Another source of a stripped head will be allowing the driver to slip within the head while applying heavy pressure. Make sure you have good contact and good bearing. Don't ever go at a screw in any manner other than square to the head. I don't want to think what sort of grief that might cause. So, BE SURE and apply a good amount of pressure.
Here is the lens with the upper portion of the barrell housing removed. Once removed it will reveal the focus gearing mechanism. It consists of several (an inner and outer) ring gears and several smaller drive gears.
The manual focus ring is just below the arrows and is still operable at this stage. I worked it around a few time to see if I could find a problem, but didn't notice anything obviously out of whack. I didn't really want to tear into this thing any further unless I had to, so I went and got an halogen lamp and looked very carefully around and, low and behold, I found the problem. There was a loose screw floating around in the mechanism. Next was to find out where it had come from.
It didn't take long. It was pretty obvious, though I had to rotate the focus mechanism to reveal the spot. There are holes in part of the workings and there is no other reason for their existence than to provide access to a screw. Here's the empty threads. That's the same hole in the photo above.
Now I can head to the mountains and give this baby a workout at the elk rut, where it failed last year.
Now I can head to the mountains and give this baby a workout at the elk rut, where it failed last year.
I came across this article while doing a Google search for Bigma and some other term i can't remember. Most results were reviews and nothing about repair. The problem with my Sigma 50-500 APO HSM lens was that the barrel was a bit loose, not the mount. The lens focused fine but at the moment of snapping a picture the focus wouldn't be spot on. That's because the barrel had some jiggle to it, 1mm approximately. I saw this walk-through and decided to give it a shot, i started following the steps (which by the way are perfectly illustrative once you have the lens in front of you) and at the point where i exposed the metal shins i could clearly see the 3 screws loose. I gave them a good tighten and the barrel had that awful jiggle no more. Then i worked my way backwards and everything worked perfectly.
ReplyDeleteNote: The first try didn't actually work perfectly, I neglected to check the proper fitting of the components of the aperture ring (a small metal "pendulum" has to slide along the inner part of the ring) . Also while checking the problem, a very small metal ball bearing which works as a stop and makes the ratchet noise of the aperture ring fell out. I fitted it back in place and proceeded to properly assemble the lens. Then it worked perfectly.
Good thing i didn't have to send my lens for tightening with such an easy procedure.
Thanks so much to the detailed article and the previous commenter!
ReplyDeleteI had precisely the same issue described in the comment with my Bigma. Slightly loose barrel, about 1mm play. I was afraid I had caused serious damage by banging the lens around or accidentally carrying it by the camera body strap. Fortunately nothing so dire.
I would add that for this specific repair, the instructions are much simpler.
1 - remove the four screws on the silver 'mounting flange' (picture 1)
2 - *CAREFULLY* pull up the aperture selection ring. It is still attached by a ribbon cable so be gentle.
-This is as far in as you need to go-
You are now at Picture 2 above, but with the inner part still connected.
3 - inside the housing on the outer ring are three screws. You probably need to move the flanges mentioned to get to them straight on, but these will stay in order doing it this way. Give the loose screws a good tighten as noted and reassemble. On my Bigma, two of these screws were loose and after tightening and reassembling all was perfectly back to normal.
The whole process should take you about 10 minutes.
Happy shooting :-)
Thanks for the comment. It should be noted that the BigMa has a noticable and quick bang or collision of parts when the zoom ring is moved abruptly. Once I forgot to lock the zoom, picked up tripod with camera and it "banged" out to it's limit and made a really loud noise. I suspect this sort of situation could loosen a lot of things. It also happens even when I am moving the zoom on purpose. Shooting racing events, I get a bit excited and forget to be gentle. Be gentle with your zooming as much as you can.
DeleteAlso, if you add a bit of lock tight when replacing the screws, it would probably be beneficial, however, I am not going to tell you which lock tight to use, as the wrong one might cause a screw to be permanently bonded. Being as small as they are, it would be easy to strip a head right out of one. So, consult someone smarter than me if you do this.
Hi,
ReplyDeleteYour post inspired me to open up my lens as I bought a Sigma 50-500 with a lot of dust in between the first and the second element (front)
I want to clean it.
So I managed to remove the ring on top of the first lens element. But I cannot remove the lens to clean the inside.
So should I try unscrewing the 6 screws behind the barrel holding the second element? Or is there a way to remove the first element from the front.
Please advice
Regards,
Aj
Old thread but yes undo the six screws and the front element comes away. It is one big lens.
DeleteNow the face of the second and moving zoom element is exposed and you need to lock the zoom at 100 or it will protrude and get scratched. I have yet to find the way to remove the second element to get at the mould behind it.
The screws are JIS cross head but good pro toolmaker quality Phillips 00/000 do fit, not the normal PHO size but smaller and not the made of cheese diy prosumer (cof) type screwdrivers. Driver tip must be sharp and hardened, don't let it slip because the screws are soft and they probably used a thread-locking cement during assembly. Problem here is Phillips drivers are imperial and Japan is very metric, they cannot do feet and inches at all..
Those six outer screws are a self-tap type into plastic. At the other end they are all metric machine screws, probably non-standard pitch japanese super-fine metric specials so don't lose them. Green baize on the bench like a jeweller to catch bits.