Short Back Focus Length Mod for ASI585MC

The model provides a modified shell for the planetary camera ZWO ASI585MC to replace the original part.

It converts the back focal length to 12.5mm, 5mm shorter than the original 17.5mm, to allow installation of lenses with shorter back focus lengths like CS mount lenses and other CCTV lenses (adapters are not included in this model).

It also replaces the original proctection glass with 1.25" filter thread to allow rear mounted filter options. You can install either a 1.25 inch filter, or unmounted 27.5mm round filter with 1.25 inch filter retaining ring. It is recommended to use filters with a thickness of 2mm, which is the same thickness of the original protection filter, to keep the setup nearly parfocal.

You will need 4 M2.5 hex nuts and 4 shorter M2.5 screws (optional) for installation.

*Update for V4: changed the depth of the nut hole so can use M2.5 x 22mm screws for seamingless experience.

Photo 1: without filter
Photo 2: configuration with 27.5mm unmounted filter & retaining ring.
Photo 3: configuration with 1.25" filter
Photo 4: configuration with 5mm M42*0.75 extension tube. It restores the original 17.5mm back focus length.