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09-23-2013, 09:43 AM   #1
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Pentax-F 35-70 front barrel came off!?

Okay so I was trying to screw on a lens shade on my 35-70 lens when the front element came loose.
You can screw it back in again but it doesn't link up with the focus wheel.
Before I give up and put it in my spare-parts bin does anyone know how to do this?

09-23-2013, 02:21 PM   #2
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See those two tabs, sticking up from the back of the front barrel assembly? (Here's where shallow DOF is not your friend.) There are two smaller plastic tabs which have broken off from those. If you look closely (not visible in this picture, but on the actual piece) you will see the remnants of where the tabs have broken off. They point radially outwards, to engage in slots which run longitudinally along the inside of the main assembly. You can see the slots by looking down the main assembly with a flashlight. The tabs are supposed to engage the slots, so the front assembly will not rotate.

Normally, when you rotate the focus ring, the front assembly is restricted from rotating, so the helix will extend/retract it. Since the tabs are broken, the whole front assembly rotates with the focus ring, which doesn't accomplish anything useful.

You might be able to fix this by procuring some small precision screws, to serve in place of the tabs. I'm thinking a screw with no head, more like a dowel with some screw threads on the end. Also, you might get away with just putting in one screw, since you only need one to keep it from turning.

If you go this route, you would be better off disassembling the lens further, so that you can get the fix installed correctly. That said, it may be possible to "snap" the front assembly in place, if the replacement screws are not too long, and you are careful about the orientation of where the front assembly should go, to engage the helix correctly. If you get the orientation wrong, your lens will not focus close, or won't focus to infinity. Also, you might just end up breaking the screws off. So if you are going through the trouble, I'd disassemble the lens further.

I broke an F 35-70 a similar way, but haven't gotten around to trying to fix it. Good luck and if you are able to fix it, please post a follow-up.
09-23-2013, 02:53 PM   #3
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Oh I see. Was afraid that something would have broken of. But yes it seems to be exactly like you said. Four small plastic pigs on the tabs that guide the lens along the barrel. I'm gonna look around for some small enough screws or something to replace them with tomorrow.
09-23-2013, 03:13 PM   #4
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If you are in the US and really want to save the lens, contact Eric at Home

He will be able to tell you if the lens has available parts and what it might take to fix it.

09-23-2013, 03:36 PM   #5
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QuoteOriginally posted by crewl1 Quote
If you are in the US and really want to save the lens, contact Eric at Home

He will be able to tell you if the lens has available parts and what it might take to fix it.
Unfortunately I'm in Sweden. Leaving for France in four days to work on a vineyard for a month. Really wanted to bring this lens since it's my only zoom and I'm looking at saving weight.
09-23-2013, 04:56 PM - 1 Like   #6
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As an alternative to using screws, I have successfully repaired this type of damage in the following way:

1.) Cut a slot where the tab used to be.
2.) Glue a small piece of plastic.
3.) Shape the added plastic with a small file.

The trick, whether you use screws or follow my method, is that you need to make sure that the new tabs align perfectly with the grooves so that the assembly will slide smoothly.

To re-attach the front assembly, you need to first of all loosen the lens groups from the housing.

1.) Remove the dress ring / bezel on the front by gently lifting the ring with a small precision screwdriver. Be very careful not to slip and scratch the lens. For safety, you may want to use non metallic tool by crafting a wood or plastic stick. The ring is held in place by three plastic tabs and just clips on and off.
2.) You will now see four screws holding the lens group to the housing. Just loosening the screws is enough. No need to remove them.
3.) The lens group should now turn freely from the housing.
4.) Zoom the lens in to 70mm position.
5.) You should now be able re-insert the housing without too much trouble. Make sure the tabs are aligned properly to the grooves.
6.) Turn the lens group so that it engages the focus helicoid.
7.) Now, you will need to adjust for infinity focus. Set the focus ring to infinity and turn the lens group either clockwise or anti-clockwise to achieve correct focus. When set, tighten the four screws without moving the focus setting.

Good luck!

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