Originally posted by woody54 
Will admit to being ever so slightly bemused and perplexed by crop factor physics when comparing MFT to FF images. Does that apply only to use of adapters without optical glass when mounting FF lenses to MFT? Do Metabones Speed Boosters and other manufacturers of adapters with optical glass also able to reduce focal length of FF lenses? One manufacturer's webpage suggests focal reducers act like teleconverters in reverse. Have checked the Metabones website it would seem that no K mount or M42 screw mount to MFT is currently available.
Yes focal reducers literally act like reverse teleconverters. They take a larger image circle and compress it to fit a smaller sensor this concentrates the light resulting in an aperture speed increase. However the optical demands are very high and only a few brands work well wide open.
The Metabones solution most often recommended for k to m43 appears to be to use a Canon EF to m43 version and pair it with a thin k to ef adapter. Also the ultra (non xl) tends to give the best optical results.
Post #11 by woody54
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