The best solution of 55mm back focal length

The back focal length is advised by telescope manufacturers. Since most telescopes have a 55mm back focal length, we are here to provide detailed instructions for all ASI cooled cameras.
Please be noted that this tutorial only applies to 55mm back focal length.  And some adapters are not included in your camera box, thus you might need to purchase them separately.

1. 4/3”, 1” and small format cooled cameras:

ASI1600/294/183/533/991/990

1) Without filter drawers or filter wheels:

2) With 1.25”/36mm/31mm EFW:

3) With 2” EFW:

Note: The total back focal length of this solution is 56mm; The two adapters T2-M48 16.5mm and M48-M42 could be replaced by the M48-M48 16.5mm extender.

Note: The total back focal length of this solution is 56mm; The T2-tilter needs to be bought separately.

4) With 2” filter drawer:

Note: The two adapters T2-M48 16.5mm and M48-M42 could be replaced by the M48-M48 16.5mm extender.

5) With OAG-L and 2” filter:

If you have an OAG-L, but do not have a filter wheel to reach 55mm back focal length. Then you can use the M54 adapter instead. It also allows you to add a 2” filter into the image train.

2. APS-C cooled cameras:

ASI2600/071

1) Without filter drawers or filter wheels:

2) With 36mm EFW:

Note: T2-T2 2mm adapter can be found in the package of 36mm EFW;

Note: The M42 sensor tilt plate attached to the camera needs to be taken off. You may need to re-adjust the tilt when re-installing the plate; The original OAG can not be replaced with OAG-L, but if you have the M68 OAG, you can use the M68 OAG instead; This method does not support the telescopes with M42 threads at the end side.

Note: This method only supports the telescopes with M42 or M48 threads at the end side. The M42M-M48F 22.5mm extender needs to be bought separately.

3) With 2” EFW:

Note: The total back focal length of this solution is 56mm; The two adapters T2-M48 16.5mm and M48-M42 could be replaced by one adapter M48-M48 16.5mm.

Note: The total back focal length of this solution is 56mm.

Note: The M42 sensor tilt plate attached to the camera needs to be taken off, and you may need to re-adjust the tilt when re-installing the plate back; The original OAG can not be replaced to OAG-L, but if you have the M68 OAG, you can also use the M68 OAG instead; This method does not support the telescopes with M42 threads at the end side.

4) With 2” filter drawer:

The two adapters T2-M48 16.5mm and M48-M42 could be replaced by one adapter M48-M48 16.5mm.

5) With OAG-L and 2” filter:

If you have an OAG-L, but do not have any filter wheel to reach 55mm back focal length. Then you can use the M54 adapter instead. It would also allow you to add a 2” filter into the image train.

3. Full frame cooled cameras:

ASI6200/2400

1) Without filter drawers or filter wheels:

Note: The above two solutions will both block the sensor a little bit.

2) With 2” EFW:

Note: The M42 sensor tilt plate attached to the camera needs to be taken off, and you may need to re-adjust the tilt when re-installing the plate; The original OAG can not be replaced to OAG-L, but if you have the M68 OAG, you can also use the M68 OAG instead; This method does not support the telescopes with M42 threads at the end side.

3) With 2” filter drawer:

Note: The back focal length of this solution is 56mm.

Note: This solution only applies to telescopes with M68 interface threads. If the threads of your telescope is M42 or M48, then we recommend you DIY the relative adapters or choose the 2” EFW.

4) With OAG-L and 2” filter:

If you have an OAG-L, but do not have & want to use any filter wheel to reach 55mm back focal length. Then you can use the M54 adapter instead. It would also allow you to add a 2” filter into the image train.

 ASI camera connecting with OAG diagram：