In this article you will learn how to connect a ZWO ASI6200MM Pro, a ZWO 2″ EFW and ZWO M68 OAG to get the best back focus length of 55mm.

All these parts can be purchased from 365Astronomy or their dealer network.

For a quick overview see the below calculation and diagram showing all the parts with optical lengths:

ASI6200MM Pro camera (12.5mm）+ 2”EFW（20mm）+ M68 OAG（17.5mm）+ sensor tilt adapter（5mm）=55mm

And here are the detailed steps:

1) Disassemble the 5mm sensor tilt adapter on the main camera with the help of a screwdriver:

2) Remove the back cover of the 2″ EFW (there are two versions ZWO: 5-position and 7-position):

3) Disassemble the filter wheel carousel (Note: Please do not disassemble or move the central screw of this carousel, otherwise the EFW will be damaged):

4) Align the four screw holes of the EFW with those in the four corners of the camera chip as shown below:

5) Tighten the screws at the interface between the EFW and the main camera:

6) Install the filter wheel carousel:

7) Fix the ZWO M68 OAG to the back cover of the EFW (Note: You might have to reposition the prism to make sure it would not block the sensor):

8) Fix the 5mm sensor tilt adapter to the ZWO M68 OAG:

9) Attach the back cover of the EFW to the front cover:

10) Installation complete.

Note: Please make sure the prism does not block the light from your telescope to the sensor.

Adjust the focal length of a guide camera by using the guide knob.

Would be better if you finish the above steps during daytime, as it is very difficult to adjust it accurately at night.

Above Instruction is courtesy of ZWO (with some text corrections from 365Astronomy).