Anjin, I don't think our opinions about the 1.4x are all that different. I think if you look at my list, you'll see that I am pretty clear about when the 1.4x will not impact your images. However, if someone is buying a $1700 180-600 f6.3 to put a 1.4x converter on it and expecting "excellence," then I think they will be disappointed. In my humble opinion, there are better ways to get to the ultra telephoto range without having to convert and f6.3 lens to an f/8.8 lens.
The following are my suggestions...
1. If you are using a 47MP camera and you need more focal length, shoot your 180-600 in DX crop mode. Doing this will get you to a 900mm field of view while maintaining a faster maximum aperture and autofocus.
2. If you want the best quality you can get for less, get a 500PF and use the TC1.4III with FTZ. This will get you 700mm f/8 and if you need more, shoot that at DX crop to get to slightly over 1000mm field of view at f8.
As good as modern zooms are, they are a compromise optic. I carry a mix of zooms and primes, I just recognize the limitations for my shooting needs.
Finally, for the record... I have ordered the 180-600 and I am hoping that it is a strong lens. I loved my former 200-400 f4VR with all of its warts. A lens like this allows you to be a flexible shooter and to travel with less gear. Once I eventually get my lens, I will do a controlled comparison between it and my other lenses...
cheers,
bruce
I've never been a fan of the suggestion that you can get more focal length by shooting in DX mode. You can change your field of view by doing that, but you are absolutely not getting anything equivalent to a longer focal length.
A narrower field of view is one factor in getting a longer focal length, though it's not nearly as meaningful a factor as it once was in the days of film or the earlier days of lower megapixel digitals.
Another factor, and the one I'd argue most people are actually looking for from longer focal lengths in 2013, 2018, 2023, etc., is increased magnification/the ability to resolve more detail at greater focal distances. People are looking to be able to photograph, say, an egret at a certain distance and have it fill their frame rather than be 50% of the frame, or get it to 50% rather than only 25%, so that the egret will look sharper and have more texture and more detail. Now shooting on a true DX camera can
sometimes give you this if its sensor is adequate. For instance, some APS-C cameras out there have something like 30 MP sensors, which really does give a bit more detail to subjects at a certain distance than DX mode on a 45 MP sensor.
However, given that you are just cropping off the FF edges of a FF sensor and taking the APS-C portion of it, you're gaining no detail or magnification whatsoever.
A teleconverter, on the other hand, can at least theoretically provide more real detail as it is an optical magnifier. It's true that oftentimes the resolution of a lens being magnified by the TC is insufficient to meaningfully yield more detail and so in practice using the TC is not any better than just cropping an original - either in camera by changing to DX more or in post. However, a TC at least has the
theoretical possibility of providing more detail on a more distant subject in a way that switching to DX mode never can. This is why people like to at least give them a try and hope they'll work well with a given lens. If that doesn't work, it doesn't work, but I've never understood how switching to DX mode is supposed to yield any improvement in this regard.