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Removing the dent in the filter ring
Removal and cleaning the front element group
Removal of the mount and auto diaphragm coupling
Disassembly of the lens barrel
Remove and clean the rear element group
About The Lens
When this lens, when first manufactured in 1964, was one of the sharpest 50mm lenses available. Even now it beats most commercial lenses, and I suspect more than one or two 'pro lenses. In fact this can be said about all of the Pentax Takumar lenses.
If you get the chance to buy any of the series you are unlikely to be disappointed. Even if less than perfect, they are still very good. You can sometimes find them in 'car boot' sales, at a range of prices and conditions, and various Internet auctions. I have even found them in the 'surplus stock' bin in camera shops! (It's usually not worthwhile for the shop owner to spend time cleaning the dust of such an old lens. Besides, he might find something nasty under the dust anyway. So he won't get very much for an example in anything but 'mint' condition. But I'm not complaining!)
The lens went through a number of variations and improvements until eventually discontinued in 1975. The original version had 7 elements arranged in 8 groups. This changed to 6 elements in 7 groups in 1966. In 1972 the lens gained a multi-coating, and a lug for use with Spotmatic ES and F models. The later super multi-coated types are to be preferred over the earlier single coated types, simply for the sake of the better coating, but be aware that the lug may cause problems with some M42 mount cameras.
Other variations include different numbers of diaphragm blades, ranging from six to eight. This article shows the disassembly of a late 8 blade type.
Problems peculiar to this lens type.
Many examples show yellowing of the inner elements. This is due to the use of radioactive Thorium in the glass formulation. I believe that the cause of the discolouration may be attributable directly to the effects of the radiation itself as the Thorium decays. However, there is no need to worry, the level of radiation is very low, and is mostly stopped by the glass anyway. I am told that some lenses used for aerial surveillance in WW2, are hot enough to fog film after a few days!
This can (Reportedly) be rectified by exposure to UV for a period of two or three weeks. This method works quite well if the source of UV is Californian sunshine, but living in Britain I have not been available to verify the sunlight cure. It is claimed that artificial UV lighting will clear the glass in a little more time. My own experiments suggest that only 'hard' UV will suffice. (The sort that is produced by tanning lamps, or (more extreme) arc-welding equipment.) This type of UV can also be harmful, and can cause severe burns and cataracts, so caution is advised.
However, for many users this may not be a problem, as it is usually only a very light 'straw' shade, and at worst adds a slight warmth to colour Images.
As with other lenses problems encountered may include fungal growth and stuck diaphragms. Provided the fungal growth is slight the lens performance will not be discernibly affected, but cleaning the fungus out is still advisable. Stuck diaphragms are usually due to grease on the blades, which will need cleaning. Both of these operations will require disassembly of the lens.
The Subject
The lens I am dismantling here came with a SP500 bought on the internet. It has a dented filter ring, a sticky aperture, discoloured, elements, fungus, and it appears someone has already attempted some repair, and scratched the front trim quite badly. All these factors usually add-up to an junker, but it makes an ideal subject for this purpose!
This lens often baffles attempts to dismantle it, but with the right tools, and know-how it is not normally too difficult to do. In the case of this lens the dent in the filter ring is going to be the most difficult obstacle.
As always in camera repair , the first place to start is with a careful examination of the subject.
OK the filter ring and the front trim on this lens is damaged. The front trim damage probably results from a previous attempt to open the lens.
Notice that there is no obvious means of unscrewing the front element.
There is no obvious means of access from the rear either.
The only evidence of any means of ingress are some small grub screws on the body. These are not the answer.
To access the screws we need to get to we must first remove the front trim. This is screwed into place using the filter thread. We will not be able to dismantle the lens unless the filter ring is straightened.
There are a number of ways of getting 'digns' out of filter rings, some are more drastic than others, but none can rectify a severe dent in the ring. If the ring cannot be fixed, the lens is scrap.
My first line of attack is to use a pair of jeweller's wire forming pliers to get the worst of the ding out of the lens.
The technique is to start at the centre of the dented section and squeeze firmly. Then working symmetrically outwards from the centre work towards the end of the dented area. You may have to repeat this process several times.
You are aiming to get a straight-sided cylindrical profile, of the correct radius. You can use an old filter to gauge your progress.
In this case a perfect result will be impossible to achieve, and I will have to be satisfied when I get to the point at which I can remove the trim.
Removing the trim can normally be done with a rubber tool to provide a friction grip. Such tools can be had from a number of sites on the Internet, but they can be expensive. At at a pinch one can be improvised with a suitable wooden dowel with a piece of rubber sheet glued to one end. You might even find a rubber bung from a homebrew supplier may fit the lens in question.
The tool I used is a multi-sized type designed for the purpose. It comprises a set of concentric cones, which I add or remove to obtain the right size.
You don't want to push on the lens itself, this obviously risks scratching the surface. With this tool I can just remove the smaller cones from the middle. Some tools may need hollowing with a sharp knife.
In this case I can't get the dent out completely. The ring is very tight, and I can't get enough grip on the trim to unscrew it completely.
So, I will have to resort to plan B.
Plan B involves using a lens 'spanner' to get more leverage.
This is the lens spanner I propose using. These tools are available from specialist tool suppliers. This is a relatively inexpensive one, costing about ten pounds.
You can improvise using a pair of dividers, of the sort you can find in a 'one pound' shop. You may have to file the points a bit, but it will work almost as well.
I have often found that in some situations it works better!
To do this I will have to make two small holes in the trim in order to give the spanner purchase. To do this a small drill, of 1mm or less will be used in a pin vice.
You need to carefully drill two holes opposite each other in the trim. Try to pick points where they will not be quite so visible once you have finally cleaned things up.
In this case I tried to get one of the holes in the middle of the P in Japan.
The amount of force applied will depend on how well you have managed to fix the filter ring. No matter how careful you are however, it is unlikely that the holes will be very tidy after the trim has been removed. So you will probably have to clean this up afterwards!
Finally, the trim is removed! It is probably clear from the picture that it put up quite a fight! A bit of 800 grit abrasive paper, plus some elbow grease and paint will tidy that up.
Of course if you are not concerned about the external appearance, you can leave it. It's not as if it would affect the image quality!
After removing the trim, we now have access to three small screws which retain the forward part of the lens barrel
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Having removed the forward barrel, the front lens group may be removed.
Note the signs of fungal growth on at the borders of the lens. This is not yet serious enough to degrade the lens performance to any significant degree, but it should be removed lest it get worse.
Removing the group is simply a matter of unscrewing.
You can see in this view of the lens that the fungus is on the inner surfaces. (It almost invariably is.) This of course means I will have to further disassemble the front group to clean it off.
Disassembling the lens group is relatively straight-forward. Just make a careful note of the order of removal of each element, and which way around it is mounted.When re-assembling, tap the housing to ensure the lens is properly seated before locking it down.
Cleaning fungus has a few options and suggestions for cleaning and killing fungus. If the fungus growth is really bad however, the coating of the lens may be damaged, and while the coating can be replaced, it is unlikely to be economic for a lens that can be got so cheaply!
With the front elements removed the diaphragm is available for cleaning. It will be easier however if the lens is dismantled to the point where the auto diaphragm actuating mechanism is uncovered.
This is due to the fact that the aperture will lock fully open when the lens is not mounted on the camera, and you will need to operate the diaphragm during the cleaning operation.
Removing a further three screws allows removal of the focusing ring.Make sure that the washers are kept safely. These are needed to properly secure the ring.Set the focus to infinity before removing the ring. This will help when you re-assemble the lens.
Now the indexing ring can be removed. Those small 'grub' screws we saw earlier need to be loosened to free it. It is not necessary to remove the screws completely, which is just as well as they are very easily lost!
Before removing the aperture ring take note of these triangular notches. Notches like this invariably indicate the presence of a spring loaded ball bearing. These are very small and very often are catapulted across the room under the force of the spring when the ring is removed.
To reduce the risk of losing the ball, I usually place the whole thing inside a plastic bag before removing the ring. This at least means I only have to search the bag, and not the entire carpet!
Also note the protruding screw. This screw acts as the end stop or the focusing ring. It is not necessary to remove it.
In this case the grease has become so old and sticky that the ball and spring have not jumped out! Nevertheless they will have to be removed as they are going to pop out sooner or later. A drop of lighter fluid will dissolve the old grease.
The grey line here is caused by tiny particles of metal worn away from the aperture ring by the ball, scraping the finish away. This is quite normal in a lens this age.
Make sure you clean all this off before re-assembling. A tiny blob of fresh grease should be put into the hole when re-assembling.
Unless you need to clean all the old grease off the focusing screw, I don't recommend the removal of the inner barrel. It can be tricky to re-fit.
In any case, it is worthwhile noting the exact position in case you lose it. (You should have set it to infinity earlier.)
It's not too difficult to find infinity focus on re-assembly, but you may find that if you remove the focusing screw the lens may not focus over it's entire rang unless it is replaced in the same position.
While we're here, note the position of the notch, aligning with the hole shown here.
This is a registration mark. If you do choose to dismantle the diaphragm assembly, this mark indicates the correct position to replace the fixed plate.
This would only be required in extreme circumstances, and unless you are a highly dextrous masochist, I don't recommend taking this apart.
If you do, then remove the three grub-screws and good luck!
For access to the rear elements and the diaphragm actuator, the rear housing should be removed.
To do this remove the three cross-head screws in the barrel. The rear housing should now slide off.
The auto aperture mechanism in the rear housing. Note the two pins on the left. These engage with the diaphragm actuating pin.
When not mounted on the camera the mechanism will lock in the 'auto' position. (For those with the aperture coupling ring at least.)
This places the operating arm in the fully open aperture position. Therefore the diaphragm should be fully dilated when re-assembling.
The rear of the lens showing the diaphragm actuating pin. Moving this pin from side to side will open and close the aperture. Access to this pin will help when cleaning grease from the diaphragm.
Removing the two brass lugs will allow you to remove the barrel from the focusing screw. I don't recommend doing this unless you have a problem with the focusing action. Before you do this however, try a drop or two of lighter fluid in the focusing thread, it may just be old sticky grease. This may not provide a permanent fix, but you will know what the problem is.
To remove the barrel, turn the brass ring until it unscrews. Count the turns required to do this so that you can relocate the correct start point later.
The rear element is retained by the collar at the rear of the assembly.
If you have strong fingers you can unscrew it by hand. If not a kitchen bottle cap opener can be used. The type to use is the sort with the rubber strap, which will remove the collar without damage.
With the ring removed the rear elements can be removed. Note that the innermost element cannot be removed from the back, but it is not unnecessary to take it out to clean it.
Note the yellow tint of both the elements in this picture! Some sources state that only only one element is subject to this. Clearly not the case for some examples.
The camera this came off had not been used fifteen years, and had a film already in it. On development, I found no fogging that could be attributed to radiation from the lens. So it would seem that an inch or so of air is sufficient protection! Having said that, the fungus growing on the inner element, was growing in a way I have not seen before!
To clean the diaphragm use a small quantity of lighter fluid, a small artists paintbrush and a soft duster.
A professional repairer would use a special formulation cleaner with rapid drying properties. The main reason in this application is simply the speed of evaporation. (Freon used to be used, but as this is a CFC it cannot be used any more.)
The professional fluid is expensive, but lighter fluid is quite acceptable as an alternative.
First apply a small quantity of fluid to the diaphragm ring. Applying too much runs the risk of spillage onto the rear lens element. Given that this will contain an amount of dissolved grease, we would prefer to avoid this.
Then mop-up with a piece of rag. Just dab a corner of the rag onto the ring and blades. You don't want to risk damage to these delicate parts.
Repeat this operation several times, until you are sure that the grease is completely cleaned from the blades.
While drying the diaphragm operate the actuating pin several times, this will speed up the drying process. The diaphragm will be quite stiff until the fluid is dry, so don't force it if it sticks a bit. It will free-up when it dries.
If you find the diaphragm is still sticking after cleaning, it could be because the steel blades have become magnetised. It's rare, as the blades need to be quite strongly magnetised to cause a problem, but it can happen.
The object in this picture is a tape-head de-magnetiser. I don't know how easy these are to get since everyone started recording digitally and have probably thrown their tape recorders away, but I am sure that any jeweller that does watch repairs would have one. They also occasionally turn up in car-boot sales.
In principle it works by creating a powerful alternating magnetic field, which swamps the field you are trying to eliminate. To use it you wave it about in close proximity to the magnetised object and slowly withdraw the object to a distance. This gradually reduces the magnetic field to zero, and the part is no longer magnetic.
In reality it's just an electromagnet running off the domestic AC supply, not a complicated device at all!
When re-assembling, fit the front element group before fitting the focusing ring etc.
This allows you to check infinity focus is achievable before going to far with the re-assembly.
Mount the lens on a camera, and focus on a distant object, using the brass ring. (I use Brighton Station roof, visible from my front doorstep. It's about a mile away. That's infinity as far as a 50mm lens is concerned!)
To align the aperture scale on the index ring, just select an aperture, and line the diamond with the correct f-number.
The focusing ring should be fitted at the infinity position. Re-check infinity focus before screwing it home.
There is a groove in the focusing ring which limits it's travel. When fitting, focus the lens at infinity, and rotate the ring until it stops before locking down.
The rest of the re-assembly is the reverse of the disassembly.
Conclusion
You should now be able to successfully disassemble and clean this lens, and put it back together. The techniques employed should be applicable to most manual focus fixed primes, and are good starting point for more complex zoom and autofocus lenses.
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