The Pentacon 29mm is a very cheap and very usable lens that can be used with modern DSLR cameras. However, like any other old lens, they accumulate dust, fingerprints, and other nasties internally; and sometimes the aperture blades can get sticky. Fortunately, it's a very simple lens to strip and rebuild. Here's how.Steps
- Set out your workspace. Set out at least two pieces of clean, white paper for you to put things on. Give yourself plenty of space to work with. Pour out some denatured (preferred) or rubbing alcohol or other similar fluid into a small glass.
- Focus your lens to its shortest distance.
Remove the front cover. Grip the focusing barrel, grip the front cover and twist the latter counter-clockwise. You may find this needs more force than you think.
- Remove the front element retaining ring. This unscrews counter-clockwise. Use a special tool for this purpose if you have one; otherwise, grip the lens firmly and use a screwdriver to push it. This can be extremely stiff. Be very careful; slipping and gouging your front element with a screwdriver would lead to a very sub-optimal state of affairs.
Remove the front element for cleaning later. With the retaining ring above gone, this will simply lift out Place it on a soft cloth the right way up.
Remove the second-to-front-element. This is threaded into place; you can remove it the same way you did the front element retaining ring above.
Unscrew your front aperture guide ring. You can see this when you look down into the front lens barrel; it's held in place with three screws. Undo these and keep them safe.
Remove your front aperture guide ring. You might want to use a magnetic screwdriver to lift this out.
Separate the front barrel from the lens body. This will lift out easily. Now turn this upside down, and we're going to go to the rear of this.
- Remove the rear element retaining ring. This is another of those "jam a screwdriver in and pray" notched rings. As before, be careful.
- Remove the rear group. This will drop out quite easily. Put it somewhere safe, and remember which way it came out!
- Remove the groups's housing. This is the black part of the body in which the last group you removed sat. Now, turn what's left of your lens rear-upwards. You will notice that there are three, very small grub screws near the top. Remove one of these -- you only need to do one to free the housing, and undoing all of them may or may not make this part tricky to re-align. If you don't need to undo it all the way, don't. These screws are extremely fiddly to re-fit. Otherwise, put the screw somewhere safe -- these are extremely easy to lose.
Remove the last element. This is held into place along with a retainer with two holes in it. You might get lucky and be able to jam a nail into one of these holes and turn it, but the farm should not be bet on such. If you have a pair of circlip pliers, these will work much better. Unscrew it counter-clockwise and drop it out.
- Loosen the rear aperture retainer's grub screw. Immediately underneath the small grub screws holding the second group's housing in place (one of which you unscrewed earlier), you will see one more, even smaller grub screw. Loosen this. Again, don't remove this all the way if you can possibly avoid it. This is even smaller and fiddlier to re-fit than the last one you removed, and even easier to lose.
Remove the rear aperture retainer. This should simply screw out counter-clockwise; removing this will expose your aperture blades.
- Make a quick drawing of how your aperture blades interact with each other. You'll need to refer to this later.
Remove your aperture blades and place them in your alcohol. Be very very careful about how you do this. Aperture blades are, as you will notice, extremely thin and very easy to bend. You may find it useful to lift out the rear aperture guide, complete with blades, and simply drop them into your glass of alcohol. But if you lift them out individually, do so very carefully with tweezers or a magnetic screwdriver. If you're using the latter method, then remove the rear aperture guide too.
Clean your optical elements. If they're not too bad at all, then blow any large particles away with a blower brush, and use a soft, lint-free lens cloth to polish them. Otherwise, contact lens cleaning fluid might do the trick. Place them somewhere safe and clean.
- Clean out your housing and your aperture blade guides. Wiping them with some alcohol and a dust-free cloth should do the trick.
Refit your front aperture guide. This was the one you removed earlier, which was held in place with three screws. Don't do these screws up tight yet.
Drop your rear aperture guide into place. The holes in the latter should roughly line up with the slots in the former.
- Remove your aperture blades from the alcohol. Allow them to dry naturally; placing them directly under a lamp should help to evaporate the alcohol.
- Take a break. Get a cup of tea or coffee and a snack, some fresh air, and a smoke if you're that way inclined. Seriously, you'll need it.
Re-fit your aperture blades. This is the most difficult, time-consuming part of the rebuild. Refer to the diagram/scribble you made earlier and take your time. Use tweezers to put them back into place. When you find yourself having to slide one aperture blade under another, you may find that lifting the latter with a magnetic screwdriver helps, too. Remember that bending or breaking one of these could make your lens a write-off, so be careful. Take breaks as often as you need to.
Verify that the aperture opens and closes correctly by moving the lever on the side back and forth.
Re-fit your rear aperture retainer. Fasten the grub screw you undid earlier when you're done. Open and close the aperture again to make sure everything is okay.
- Re-fit your rear groups. This is exactly the opposite of undoing them; there should be no surprises. Use a lens cloth to clean them both before and after fitting.
- Open your aperture fully and drop your front barrel into your lens body. You'll notice that the aperture lever should, on auto lenses at least, line up with a prong inside the lens body. Push your stop-down button (or aperture pin on M42 lenses) to ensure that the aperture is opening and closing properly.
- Check your apertures again. Stop the lens all the way down to f/22 with the aperture ring on the body, and hit the stop-down button. You'll pretty much have to guess what looks right and what does not; wide-open, the aperture should not obscure the rear elements too much (if at all), and stopped down, it should not be a tiny pinhole. Adjust the front aperture guide ring until it looks right. When it does, tighten the three screws that hold it in place.
Re-fit your front elements, ensuring that you put the groups back in the right way up! Again, there should be no surprises doing this; it's the opposite of removing them. And again, clean your groups twice, once before fitting and once right after doing so. Re-fit your front cover, too.
- Take your camera out and get some photographs. Make sure that your lens focuses and stops down properly. If it doesn't focus properly, you may have gotten one of the groups fitted the wrong way around; if it's sticky stopping down, you may have contaminated your aperture blades with dust, hair or something else.
Tips
- Wash your hands regularly with plain bar soap. Even normal fingerprint grease can cause aperture blades to stick together and make them very awkward to re-fit, for example.
Warnings
- It is a good idea to wear gloves when doing this work; keep your workspace as clean and dust-free as possible.
- Don't smoke around solvents. Make sure everyone knows it's there, and doesn't mistake it for water.
- It bears restating as often as possible: be very careful with your aperture blades.
- A set of precision screwdrivers.
- A normal flat-bladed screwdriver for removing retaining rings. If you're not feeling brave, then you can buy tools designed specifically for removing this sort of thing.
- A magnetic screwdriver.
- Circlip pliers.
- Clean, white sheets of paper.
- Rubbing alcohol, or some other strong solvent, in a glass.
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