Compared to many other bridge cameras out there 600mm seems rather modest so why would one buy this camera rather than one with a smaller sensor but a 1200+mm upper range? This isn't, I hasten to add, a criticism but just a question!
John, you are right, that when chasing 'geewhizzits' and lbj's that even 600mm can seem to come up well short. I hope the following helps .....
This Sony has an in-camera crop mode that will shoot 900mm images at 10MP, and 1200mm images at 5MP. I haven't read any specific confirmation for this new IV model, but I take it that it is at the full whack of 24fps - holey! :eek!:
The big headlines (apart from the downsampled 4K video - far preferable to the pixel binning method that even the mighty new Nikon D850 FF jobbie uses) are the combination of
*phase detect AF from the upper range DSLR models (performance to be confirmed in testing, but expected to be a quantum leap better than other bridge cameras on moving subjects - BIF, and kids hopped up on red lollies etc

*24fps (the full AF tracking rates may be less - keep an eye on the tests)
*in concert with the punching 1" Sony BSI sensor + fast Zeiss quality glass which should offer subject freezing shutter speeds.
*In an all-in-one sealed wideangle to telephoto zoom range and fast aperture speed camera that NO DSLR CAN MATCH, let alone other bridge cameras. :cat:
With the long legged competition, there is no free lunch, and those tiny sensor super zooms of 1200-2000mm get those seemingly large figures at a cost .....
*slow telephoto apertures of around ~f6.5 ...... the quality Zeiss lens of this new Sony at f4 is in another league.
*some are just offering jpeg capture, and even those that are using RAW have the pixels crammed in there like smartphone cameras ..... the 20MP sensor of this Sony is a 1" format so should offer better Dynamic Range and better less than ideal lighting conditions performance.
*mostly contrast detect AF is slower on rapidly moving and low contrast subjects which can result in the dreaded hunting for focus .... the promise is that this Sony should leave them in the dust - that is reason enough alone for picking it over the longer zoom smaller sensor bridge cameras (though like this bin vs that bin, debate often ranges strongly!

*some don't offer manual zoom so can have painfully slow racking times ..... this Sony's manual zoom ability should let you pre position it at shut down and start up times to minimize both time and wear and tear.
The bottom line is that this Sony RX10 IV should get as good or better pictures than other bridge cameras more often in much more varied (read less than ideal) conditions, and cause those lugging bigger, heavier, MFT, and APS-C setups to seriously question why. Even FF users will drool ....
This camera is a bit of a milestone! :king:
https://m.dpreview.com/samples/3529337823/sony-cyber-shot-dsc-rx10-iv-samples-gallery
Chosun :gh: