Caveat Emptor

I have been having problems getting a satisfactory field flattener for the apo. Having ordered the flattener supposedly optimised for my scope I was dismayed to find its performance fell far short of perfect with terrible coma appearing at the left and bottom of the frame. Having eliminated the scope or camera from being part of the problem I felt justified in getting the flattener replaced. Alas the replacement was identical regarding its poor performance. As an experiment I tried using the Baader coma corrector that I use on my main scope. Although not designed as a corrector for refractors it performed noticably better than the (supposedly optimised) flattener. Though still far from perfect I did use the Baader corrector on my last two images published here where it certainly gave a larger useable field. There is a universal German field flattener that has had a good review when used with the Megrez 88 but at the moment I'm reluctant to shell out yet more cash until I'm absolutely sure I am getting something that works properly.

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