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Help! Focusing Issue with Bahtinov

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I'm using a Bahtinov mask made for a 6 inch aperture on my 6 inch F4 Newtonian. However, The Central spike doesn't appear to be straight. I'll share an image I drew to simulate what I see. What could be the cause of that? Is it a bad Bahtinov mask or something with the optics? The star is in the center of the frame.


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3 minutes ago, globular said:

If you turn the mask over does the odd effect flip too (which might suggest a dodgy mask) or do you get the same effect with the same orientation (which might suggest collimation).

hmm I'm not entirely sure but I think it always the same effect no matter the orientation. I never knew collimation error could show in the spikes 😕 although collimation looks fine with my collimation tools. 

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