Some thoughts:
- A medium format SLR is definitely not the traditional tool-of-choice for street photography
- Your hit rate (both technically and creatively) will be significantly lower than with other more traditional tool choices
- Many great images have been created by photographers using cameras other than the traditional tool of choice for a given kind of image (think Avedon's 8x10 portraits)
- If you get a hit, it will have more technical credentials than 99.99% of street photography out there
I've done a fair bit of defacto street photography with the XF as part of my job in R+D. It's a great environment in which to test autofocus response. With the XF you can use autofocus even with the waist level viewfinder, which can help you be a bit less disruptive/obvious. There is also a mode on the XF for focusing to a specific distance (e.g. 6 ft) with a push of a button (whichever button you assign to it) which can serve in a similar way to the Leica M zone focus. You can also collapse the viewfinder, hold the body against yours with one hand (point forward, or cradled in the nook of your arm pointing to your side), and use the built in wireless to transmit to an iPhone in your other hand.
Bottom line: it will be more challenging, and you should expect a lot of frustration and misses, but nothing says you can't create some striking images with it.
Sometimes it's nice to challenge yourself
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