Canon New FD 50mm F/1.4 Disassembly from the Front
The following information is provided to assist people in disassembling a Canon New FD 50mm F/1.4 lens as shown below. Care should be taken with all parts of the lens, especially, the glass, the aperture blades and the threads, and the lens should only be disassembled in a clean environment. Please be aware that these instructions were developed through my experience with the lens and I am not a professional in the area. They are accurate to the best of my knowledge, but if you choose to follow these instructions, you do so at your own risk.
The trim ring of the the Canon New FD 50mm F/1.4 lens has no thread and essentially just clips onto the lens. I am aware of two methods for removing the trim ring.
The first method is to lever the trim ring off the lens from the outside as shown by arrow (1). For this I used a very small flat screwdriver and gently levered the trim ring at points around the outside of the ring. The only downside I can see to this method is that the filter thread may get damaged by the screwdriver if you slip. However, I have used this method a few times on this lens and still have no trouble attaching a filter.
The second method is to lever the trim ring off the lens from the inside as shown by arrow (2). I've seen pictures of people performing this method with a screwdriver and I expect it would work even better with something flatter. However, I did not attempt this method as I was scared to use anything metal that close to the front element of the lens.
Once the trim ring has been removed, you will see three screws which secure a bracket. This bracket holds the front element in place. Remove these screws and remove the bracket. Do not turn the lens upside down to remove the bracket as the front element is no longer secured to the lens and will fall out.
Once the bracket has been removed, take a tissue or soft cloth and place it over the front of the lens. Carefully remove the front element into/onto the tissue or cloth by tipping the lens. I did this just above a bench so there was no risk of the front element falling and being damaged.
Note that the diaphragm is now exposed an can easily be damaged. Do not touch the diaphragm with your fingers and be careful not to drop anything onto it.
The focus ring is attached by three screws. Note that the screws can be repositioned along a channel to calibrate the infinity focus. Unscrew the screws and remove the focus ring.
Rear element and internal focus ring
The diaphram can be removed from the rear element assembly by unscrewing the three screws shown in a flat circular section within the rear element assembly. The flat circular section including the diaphram can be lifted out of the read element assembly. However, it is possible to clean the element below the diaphram by having the diaphram wide open.
The rear element assembly (2) can be removed by unscrewing the internal focus ring (1). The internal focus ring has an internal thread in communication with a thread of the rear element assembly and an external thread in communcation with the lower part of the lens.
This part of the lens can be difficult to reassemble correctly. However, reassembly can be made easier by noting the position of the internal focus ring when the rear element assembly comes loose and the orientation of the rear element relative to the focus ring.
Elements of lens when disassembled
Reconnecting the internal focus ring and the rear element assembly
The rear element assembly screws onto the internal focus ring as the internal focus ring is screwed into the lower part of the lens. The internal focus ring should be connected such that a minimum focus distance and infinity focus can be achieved. I found that the best way of achieving this is to mark relevant positions of the internal focus ring when disassembling the lens.
First, line up the controls (1) and slot (2) of the rear element assembly with the controls (1a) and pin (2a) of the rear part of the lens so that the rear element assembly slides easily into the rear part of the lens. Remove the rear element assembly from the rear part of the lens, then screw the internal focus ring into the rear part of the lens to the marked position. Place the rear element assembly on top of the internal focus ring with the controls aligned and continue screwing the internal focus ring until the rear element assembly is properly attached.
If you have not marked the positions of the internal focus ring, screw the internal focus ring the whole way onto the rear element assembly then unscrew it two turns. Place the rear element assembly on top of the internal focus ring with the controls aligned and screw the internal focus ring until the rear element assembly is properly attached. Note that it can be hard to get the rear element assembly onto the thread of the internal focus ring. Don't force the thread as this may damage the thread, just be patient and find the point where the thread takes.
A protrusion on the external focus ring runs in a focus track (3a) of the rear part of the lens. If the infinity focus slot (3) on the internal focus ring does not overlap with an end of the focus track when the rear element assembly is fully screwed on, measure the offset from where the focus slot should be, unscrew the internal focus ring until the point where the rear element assembly detaches, correct the offset by screwing the internal focus ring by the offset, then attach the rear element assembly again.
Infinitly is calibrated by setting the position of the internal focus ring when the protrusion of the external focus ring is against the end of the focus track (3a). Infinity was correct on my lens when the end of the focus slot (3) on the internal focus ring was aligned with a slot (3b) in the rear part of the lens. Infinity can also be calibrated by reattaching the front element to the lens and using a target that is far away such as clouds or stars.
The remainder of the lens reassembly is quite straight forward.
Please note that when Canon FD lenses are attached to nothing, the aperture will not function. The aperture will function normally when you connect the lens to a camera, or when you connect the lens to an adapter and turn the lock ring on the adapter.
If the controls of the rear element assembly are not correctly aligned with the controls of the rear part of the lens, you may find the lens will not mount or the aperture will not work. In this case, take the lens apart again and ensure that these controls are configured correctly. You can confirm that they are working correctly by mounting the rear of the lens and trying the aperture with the lens still dismantled.