I recently purchased a flip mirror and I find it very usefull when trying to take photos with telescope. In this setup one can both view the target visually and take photos. It takes some time to get the camera and visual eyepiece adjusted, but after that is done, then one only need to flip (turn) the mirror.
When using high magnification, then eyepiece projection is good way to achieve that. The picture below shows the 2 eyepieces that are needed in this kind of setup. Camera is connected on the left (not in picture).
The photo below shows other ways to connect a camera to an eyepiece. They do work, but are not as practical as flip mirror with DSLR. It is also possible to combine these two, and use these adapter to flip mirror in place of DSLR …
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