arbitrage wrote:
The identical MFDs give TC element (Canon shenanigan) vibes. But then the weights being 1gm apart and the 600 being larger and needing those extra elements means it can't be that simple.
I searched Sony Japan to see if they have published lens diagrams but can't find any yet.
Obvious caveat that I am not a lens designer...BUT: to my eye the two additional elements with the 600mm are towards the front of the rear group. The rest of the formula looks the same, and as noted the size and weight are very similar. It doesn't look as straightforward as adding a TC at the rear like the RF lenses because that's not where the additional elements are and because TCs often have more elements. That said, it looks like it is effectively doing something similar. If you multiple the f/4.5 aperture and the 0.18x maximum magnification by 1.4x you get the 600mm's f/6.3 and 0.25x maximum magnification. I imagine there will be some people who are disappointed that the 600 isn't a more differentiated design, but at the same time I am guessing Sony evaluated a completely new design vs. these two additional elements in terms of size and weight and IQ. If this is not as simple as a rear TC then the cost to do this isn't as simple as the cost of adding a TC, though who knows if it is $1,000 more.
What would be interesting is for a reviewer to compare the 400mm+Sony TC with the 600mm and see if there is a difference in focal length and sharpness. A second comparison I would like to see is the Nikon 600mm 6.3 + 1.4X TC vs. Sony 600mm 6.3 + 1.4X TC and whether this approach paid off with similar IQ and the weight of a 400 4.5.
I'm not buying either, but if I were more into wildlife I would still go with the 600mm over the 400mm+TC based on what I have seen so far.
arbitrage wrote:
The identical MFDs give TC element (Canon shenanigan) vibes. But then the weights being 1gm apart and the 600 being larger and needing those extra elements means it can't be that simple.
I searched Sony Japan to see if they have published lens diagrams but can't find any yet.
Obvious caveat that I am not a lens designer...BUT: to my eye the two additional elements with the 600mm are towards the front of the rear group. The rest of the formula looks the same, and as noted the size and weight are very similar. It doesn't look as straightforward as adding a TC at the rear like the RF lenses because that's not where the additional elements are and because TCs often have more elements. That said, it looks like it is effectively doing something similar. If you multiple the f/4.5 aperture and the 0.18x maximum magnification by 1.4x you get the 600mm's f/6.3 and 0.25x maximum magnification. I imagine there will be some people who are disappointed that the 600 isn't a more differentiated design, but at the same time I am guessing Sony evaluated a completely new design vs. these two additional elements in terms of size and weight and IQ. If this is not as simple as a rear TC then the cost to do this isn't as simple as the cost of adding a TC, though who knows if it is $1,000 more.
What would be interesting is for a reviewer to compare the 400mm+Sony TC with the 600mm and see if there is a difference in focal length and sharpness. I'm not buying either, but if I were more into wildlife I would still go with the 600mm over the 400mm+TC based on what I have seen so far.
Sep 15, 2026 at 11:40 AM
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