The Omegon offered a considerable length of focus range of about 42mm from memory. Allowing me to both fit and remove the 2x WO Barlow to the ZWO and still reach focus. The Omegon is superbly made and has no discernable slop when locked. It allowed the removal of two 2" x 50mm extensions which always had to be extended out from their sockets by about 12mm. Just to use up some unwanted focal length. Now it all fits snugly together. As is usual with helical focusers it offers a scale for repeatable focus points. Two thumbscrews can lock the focus position when desired. It would be possible to use a motor and belt to drive the focusing barrel. It just needs an anchor for the motor.
These images are with the WO 2x Barlow on the ZWO for 2400mm focal length. The PST etalon lens group alters the focus too. Cropping around the image has also altered the scale.
The prom was highly active and changed rapidly in the run of the morning. Unfortunately the seeing became steadily worse as lots of cloud came over. So later, comparison images were rather poor. [See Left] The sky has now turned milky around the sun and it is mostly overcast.
There was some cloud clearance in the afternoon but the seeing was awful right up to 17.00.
Saturday afternoon I tried to image a small prom at 8 o'clock on the limb but the seeing was awful. As soon as I gave up the cloud cleared. Not that the seeing will have changed. The gusty wind was making the telescopes nod as well. The forecast is for gales tomorrow.
Sunday I shall try different orientations of the dome in the strong and gusty wind. A few teaser holes appeared in the cloud but the sky was milky again. There was a huge difference in brightness of nearby proms. Which made for a messy final result more like a chalk drawing.