[pmrid (Peter)]

I've made a cute 80mm F5 shortie achromat out of bits and pieces I have cobbled together. It's probably going to be used for a bit of lunar on the go but even so I would also like to flatten out the field a bit so I can have the option to use NB filters (so CA is less of a problem) for a bit of deep-sky imaging as well but those streaky stars are a real PITA that I'd like to eliminate.

But I don't want to bust the bank on this either.

Does anyone have any suggestions for a cheap generic flattener? I already have a Hotech Field Flattener but I just can't get the spacing right so I'm looking for alternatives.