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ZWO M42-M48 Adapter 16.5mm Extender Ring

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in In stock (5)
0.15 kg
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including VAT 20.00 % ( £2.58 )


ZWO M42-M48 Adapter 16.5mm Extender Ring

This adapter might help you to achieve 55mm back focus with your camera.

Example 1:

ASI071MC-C has got sensor to flange distance of 17.5mm, then you add a 21mm T2-T2 extension and then you add either this extension (16.5mm) or a ZWO OAG (off axis guider) that has got the same thickness as this adapter (16.5mm). So basically if you use an OAG then you don't need this adapter, but if you don't use a ZWO OAG then this adapter/extension is necessary to achieve 55mm back focus. Basically, this adapter replaces the OAG and provides a M48 connection to the telescope.


Example 2:

The ASI1600MM-COOLED camera has got 6.5mm focal flange distance, add a 11mm T2 extension, add a 21mm T2 extension and finally add one of these 16.5mm extensions to achieve 55mm back focus to the sensor, but with M48 connection to the telescope.

Here is a bit of history...  Many optical elements like coma correctors, reducers, field flatteners etc. have been designed for Canon cameras that require 55mm back focus to the sensor, so this is how we ended up with this figure: 55mm, however we should note that a 55mm back focus is not always a requirement and some optical elements might require a different distance or in some telescope systems you might not even need to worry about back focus (i.e. when you don't use additional optical elements...)


  • Colour: black
  • Optical length: 16.5mm
  • Overall length: 20.5mm
  • Telescope side attachment: female M48 thread (M48x0.75)
  • Camera side attachment: male T-thread (M42x0.75)

Images are for demonstration purposes only.

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