Many thanks all.
With M42 I used Gradient exterminator in Photoshop cs by drawing with the mouse a ring round the outskirts of M42, selecting "inverse" then running Gradient Exterminator, with neutral background selected. I then adjusted Levels to darken the sky, saved it as a low compression Jpeg then ran Noiseware on it with default settings. Thats it! Can use Curves in Photoshop to neutralise the sky background too, as with the UHCS filter I get a blue cast to the sky. Neutralising it enhances red in nebulae, making up for some of the loss of h alpha light in the unmodified camera.
With NGC 1535 I stacked the shots manually in Photoshop, then adjusted Levels to brighten the nebula slightly, then cropped it , keeping just the central part so I could show it here at full res.

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Scott