M39x1 extension tubes

I have several sets of M39x1 extension tubes.

1. Old four-tube set, USSR, KMZ (КМЗ).

Tube lengths: 5mm, 8mm, 16.4mm, 26mm.

2. Old four-tube set, USSR, FED (ФЭД).

The same tube lengths: 5mm, 8mm, 16.4mm, 26mm.

Why is the tube length 16.4 mm? This tube is used to mount earlier Zenit SLR M39x1/45.2 lenses to M39x1/28.8 rangefinder cameras: 45.2 - 28.8 = 16.4 (mm)

3. Modern three-tube set, China, no-name.

Tube length: 7mm, 14mm, 28mm.

These lengths were more common for M42x1 tubes, but now they are also used for M39x1.

See also related notes:

• Использование объективов M39x1 на цифровых камерах (2022-05-18)

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