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It's likely not possible to switch mounts if you also want to have a functional lens. However, without knowing what specific lenses you have, it's impossible to answer definitively.

• For electronic mounts (EF), I wouldn't bother. The internal construction and electronics could be significantly different. For instance some lens designs do or don't have image stabilization or mechanical apertures, depending on the target mount.

• For completely mechanical mounts...

  • The aperture on FD lenses is open by default, while PK is closed by default. So internally, even for the "same" lens models, the mounts may be different enough that they cannot be switched. The different default aperture positions also explains why some adapters are more complicated than others.
  • The aperture rings on FD and PK lenses turn in opposite directions. The internal construction of the lenses may be mirror images of each other. Even if they could be switched, the lenses would have to be significantly dismantled to do so.
  • If any externally visible screws don't match between lenses, it's likely the underlying construction is different enough that switching mounts won't work.

Without knowing what specific lenses you have, it's impossible to answer definitively.

• There are Tamron lenses with "universal mounts" that can be swapped. These include T-mount and Adaptall mounts.

• For electronic mounts (EF), I wouldn't bother. The internal construction and electronics could be significantly different. For instance some lens designs do or don't have image stabilization or mechanical apertures, depending on the target mount.

• For non-universal mechanical mounts, it's likely not possible to switch mounts if you also want to have a functional lens.

  • If any externally visible screws don't match between lenses, it's likely the underlying construction is different enough that switching mounts won't work.

  • The aperture on FD lenses is open by default, while PK is closed by default. So internally, even for the "same" lens models, the mounts may be different enough that they cannot be switched. The different default aperture positions also explains why some adapters are more complicated than others.

  • The aperture rings on FD and PK lenses turn in opposite directions. The internal construction of the lenses may be mirror images of each other. Even if they could be switched, the lenses would have to be significantly dismantled to do so.

Without knowing what specific lenses you have, it's impossible to tell whether it's possible to switch the mounts. However, it's likely not possible to switch mounts if you also want to have a functional lens.

• For electronically controlled lenses (EF), I wouldn't bother. The internal construction and electronics could be significantly different. For instance some lens designs do or don't have image stabilization or mechanical apertures, depending on the target mount.

• For completely mechanical mounts...

  • The aperture on FD lenses is open by default, while PK is closed by default. So internally, even for the "same" lens models, the mounts may be different enough that they cannot be switched. The different default aperture positions also explains why some adapters are more complicated than others.
  • The aperture rings on FD and PK lenses turn in opposite directions. The internal construction of the lenses may be mirror images of each other. Even if they could be switched, the lenses would have to be significantly dismantled to do so.
  • If any externally visible screws don't match between lenses, it's likely the underlying construction is different enough that switching mounts won't work.

It's likely not possible to switch mounts if you also want to have a functional lens. However, without knowing what specific lenses you have, it's impossible to answer definitively.

• For electronic mounts (EF), I wouldn't bother. The internal construction and electronics could be significantly different. For instance some lens designs do or don't have image stabilization or mechanical apertures, depending on the target mount.

• For completely mechanical mounts...

  • The aperture on FD lenses is open by default, while PK is closed by default. So internally, even for the "same" lens models, the mounts may be different enough that they cannot be switched. The different default aperture positions also explains why some adapters are more complicated than others.
  • The aperture rings on FD and PK lenses turn in opposite directions. The internal construction of the lenses may be mirror images of each other. Even if they could be switched, the lenses would have to be significantly dismantled to do so.
  • If any externally visible screws don't match between lenses, it's likely the underlying construction is different enough that switching mounts won't work.

Without knowing what specific lenses you have, it's impossible to tell whether it's possible to switch the mounts. However, it's likely what you want is not possible if you also want to have a functional lens.

• For electronically controlled lenses (EF), I wouldn't bother. The internal construction and electronics could be significantly different. For instance some lens designs do or don't have image stabilization or mechanical apertures, depending on the target mount.

• For completely mechanical mounts...

  • The aperture control levers on PK and FD mounts work opposite each other. FD is open by default, while PK is closed by default. So internally, even for the "same" lens models, the mechanics may be different enough that mounts cannot be switched. The different default aperture positions also explains why some adapters are more complicated than others.
  • The aperture rings on FD and PK lenses turn in opposite directions. The internal construction of the lenses may be mirror images of each other.
  • If any externally visible screws don't match between lenses, it's likely the underlying construction is different enough that switching mounts won't work.

Without knowing what specific lenses you have, it's impossible to tell whether it's possible to switch the mounts. However, it's likely not possible to switch mounts if you also want to have a functional lens.

• For electronically controlled lenses (EF), I wouldn't bother. The internal construction and electronics could be significantly different. For instance some lens designs do or don't have image stabilization or mechanical apertures, depending on the target mount.

• For completely mechanical mounts...

  • The aperture on FD lenses is open by default, while PK is closed by default. So internally, even for the "same" lens models, the mounts may be different enough that they cannot be switched. The different default aperture positions also explains why some adapters are more complicated than others.
  • The aperture rings on FD and PK lenses turn in opposite directions. The internal construction of the lenses may be mirror images of each other. Even if they could be switched, the lenses would have to be significantly dismantled to do so.
  • If any externally visible screws don't match between lenses, it's likely the underlying construction is different enough that switching mounts won't work.