We often receive enquiries about how to obtain the correct spacing between a camera’s sensor a focal reducer or field flattener – such as a Celestron EdgeHD reducer and a deep sky imaging camera.
If you want to use a field flattener or focal reducer with your camera, the camera’s sensor will need to be accurately placed at a specific position to get the best image quality. You can use fixed-length spacers (extension tubes) to help with positioning, however the problem with these is that, depending on your configuration, your sensor may still be slightly too inward or outward from that specific back focus distance point.
To get that perfect spacing Baader offer two variable length T-2 extension tubes to enabler you to “fine tune” your camera to get that perfect spacing for your set up.
- Baader VariLock 29, lockable T-2 ExtensionTube 20-29mm with spanner tool (T-2 part #25Y)
- Baader VariLock 46, lockable T-2 ExtensionTube 29-46mm with spanner tool (T-2 part #25V)
The 12-16mm variable extension tube consists of 3 Astro T-2 parts (#26/#34/#35) and features a locking ring. The VarLock 29 will extend from 20mm up to 29mm, with the VariLock 46 going from 29mm up to 46mm in length. Each VariLock has T-2 female threads on the telescope side. On the camera/eyepiece side, there is a removable male T-2 threaded dovetail adaptor that is held in place by 6 small hex screws. In its place you can use the supplied S52 dovetail adaptor to directly couple the VariLock to Baader’s Protective EOS Camera adaptor. All these variable extension tubes can also be used with fixed length 7.5mm/15mm/40mm T-2 extensions in order to achieve the correct spacing.
A useful and thoughtful feature of these two VariLock variable length adaptors is their graduated millimetre distance scale so you can easily see the distance-position that the adaptor is at. Furthermore the locking ring has two small elongated openings (holes) that allow you to see the distance scale underneath the lock ring. Once the correct spacing has been set you can tighten the lock ring with the supplied “spanner” tool.