Inverted Tele Converter for APS sized camera's

[hsmeets]

Hi,

Is this just a stupid idea from me? or is it not possible or......?

Given the current well performing APS sized sensors in DSLR and having a stash of lenses from you film days......why is there no inverted teleconverter that instead of extending the focal length, shortens the focal length of a lens? Just take your 1.4 50mm, put it on your APS sized sensor DSLR and with help of the converter you retain the same angle of view as on 35mm film.

[NikoJorj]

That could have sold well 5 or 10 years ago...  
And if nobody did make it then, it might be there was an optical reason, probably around the converter/lens adequation (it may be hard to make a converter that performs decently on any lens).
Or not.

[Brammers]

One of these but for cameras?  And indeed, why not one that goes from MF to FF?

It's a good question, and one that's been asked before - as you can see astrophotographers do it all the time.  I'm sure someone will give you the answer shortly - I don't know!