The GM 300mm is lighter and more compact, even with the 2X TC. That's about the advantage of that lens over the GM 600mm, not considering the price difference though. At my age, I have been using the GM 600mm virtually 100% on a tripod, while I still manage to handhold the GM 300mm even with the 1.4X TC. Using the 2X TC is a slightly different story. It is less the weight but the stability of handholding the setup, especially with the loss of 1-stop, necessitating a higher shutter speed. The advantage of f/4.0 vs f/5.6 is nothing to sneer at. You either get a faster shutter speed or a low ISO by 1-stop, and to me, that is significant.
The bottom line is, IMHO, the bare GM 600mm is optically superior to the GM 300mm plus a 2X TC.
Mar 13, 2026 at 10:10 AM
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