I’m very happy with my little Photoline 72, but with a camera sensor of any size it becomes obvious that the field is far from flat. So much so in fact that it’s sometimes difficult to get Deep Sky Stacker to stack my image frames. When a TSRED279 come up for sale used it seemed like an obvious choice to try.
Spacing between the reducer/flattener and the camera sensor is supposed to be fairly critical and the figures on TS’s website are a bit on the vague side. An email to their support people didn’t help much, so I tried to draw a rough graph from the figures they do publish and estimated the actual distance from there. I also used the 3d printer to make some spacers of varying thicknesses from 0.5mm to 3mm that would fit over a T2 thread to help with getting the spacing correct. These will doubtless come in useful elsewhere and in fact help to prevent threads on extensions and suchlike from locking against each other.
The result is a huge improvement, though I’m not sure I have things perfect quite yet. I’ve gone from having stars that were barely even recognisable as such towards the edges of the frame to this:
I think there’s more to be done here, possibly in getting the camera sensor completely perpendicular to the optical axis, as the reducer is only threaded on the camera side and has to be clamped into the end of the OTA which obviously has the potential to create alignment errors.
I’m going to give it a bit of time to see how I get on with a few images before changing anything else though.