Realize the full potential of your Baader Fluorite Flatfield Converter (BPFFC) or 2" Advanced Convertible Barlow (BARADV) when imaging by using this extension. The internal T-thread on this extension allows you to attach your BPFFC, BARADV or other accessory with male T-threads INSIDE the 2.7" extension tube. In this way, the camera, filter wheel, off-axis guider, and/or other accessories are all supported by the much more robust and rigid 2.7" tube system, and the Barlow only needs to support its own weight inside the extension tube. This is particularly important when imaging at some of the higher magnification factors achievable with the BPFFC where over a foot of extension may be used between the Barlow optic and the focal plane. The maximum OD of the T-thread accessory that will fit inside this extension is 2.5".
This 2.7" extension has an overall net spacing distance of 0.75" (19.05 mm). However, it has a net spacing distance of 0.9" (22.86 mm) for the internal optic.
Exploded diagram: Barlow Holder System Chart
In May 2021, the part # changed from A3511 to BH27-INT42 in order to more clearly reflect its function.