Altair Astro x0.6 Focal Reducer

[hograt]

I picked up an Altair Astro badged x0.6FR from a local astronomy festival at the weekend.  I've been looking for something to replace an old Antares F6.3 SCT FR from many years back, which I have kept in service as my set up has evolved.  I've had good success with it but recently i've noticed it is causing some sag because I've had to rotate my filter wheel 180 degrees as I've transitioned from observatory peer back to tripod and the additional leverage is too much for the 2" Antares camera adapter. A long story......

Anyway I was wondering if anyone had success with this FR from Altair - I can't say I'm overly happy with it given first light although it wasn't expensive (£75)

It's attached to a William Optics Zenithstar 105 F7 triplet bang on the recommended 55mm spacing between FR and CCD (through a filter wheel and spacers) and it is sold as being suitable for this focal length.  It's marketed as a field flattner.  Actually my field is pretty good at prime focus so that wasn't my primary motivation to buy.

 It's certainly increased the field of view and I'm not disappointed with the increase in brightness and reduction in exposure time.  However, the level of image distortion is severe at the edges.  This is perhaps not surprising for a larger CCD but I used an ICX285-based camera last night and this is hardly a large chip.  

So I'm wondering if those individuals with similar set up / experience of this focal reducer than point me in the right direction (i) live with it because it isn't matched to your OTA and its cheapo (ii) it can do better - go try harder.

I've attached an image for illustration - excuse the quality but this is from last night and there is only a couple of hours exposure so far and the jpeg compression is harsh.  For reference, I did also take a shot without the focal reducer earlier in the month and there wasn't significant coma.

Thanks

Martin