Focal points on Sky Watcher Equinox Pro 80mm with different Altair field flatteners

During the changeover today from 1.0x to 0.6x Altair Lightwave reducer, I determined the focal points on the draw tube for future reference.

Andy

Focal point in Sky Watcher Equinox Pro 80mm OTA with Altair Lightwave 1.0x flattener and filter wheel and Altair 183M camera used for deep sky (as I used this week for photographing M31 and M33 – so this is the focal point that is correct for night sky for 1.0x Lightwave):

Focal point 1.0x Lightwave on roof our house from log cabin (note goes up from 46mm above on night sky to 56mm below due to roof being closer to telescope):

Focal point on our roof from log cabin with 0.6x Lightwave (44mm = means that the 0.6x field flattener requires extra 12mm of back focus over the 1.0x Lightwave and suggests focal point on night sky for 0.6x Lightwave field flattener should be around 46mm-12mm = 34mm on marking on draw tube):

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