f/4.5 – Sony FE 100–400mm GM II Rumors
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Rumors are mounting around Sony’s “Alpha Residing” event, scheduled for May 14 and 15, 2026, in New York. So far, only the event itself has been officially confirmed. According to Sony, visitors will be able to try out current cameras and lenses. However, several rumor sources expect Sony to introduce or tease new products around this date. These could include the Sony A7R VI and a new FE 100–400 mm f/4.5 GM lens.
We take a look at the rumors surrounding this possible new G Master telephoto zoom.
Switch to an Internal Zoom
According to current rumors, the possible new FE 100–400 mm f/4.5 GM could feature an internal zoom mechanism. In terms of construction, this would move it closer to the Sony FE 200–600 mm G.
This would offer clear advantages for balance, handling on gimbals, zoom operation, and possibly protection against dust and moisture, because no extending barrel is moved during zooming. However, it would also likely make the lens physically much longer. For comparison, the current 100–400 mm GM weighs around 1,395 grams and measures 205 mm in length, making it relatively lightweight and compact. Exact dimensions for the new Sony 100–400 mm have not yet been confirmed.
Such a move would bring some clear advantages and disadvantages:
Pros:
- Balance: The center of gravity remains constant.
- Potentially better protection against weather and dust.
- Smoother and easier zooming.
Cons:
- Significantly larger construction.
- Higher weight.
- Internal zoom lenses can also be prone to focus breathing.
A Closer Look: Focus Breathing at Close Range
One point that remains particularly relevant for wildlife photography is focus breathing. This refers to a change in the field of view, or more precisely the effective magnification, when focusing at different distances.
Focus breathing can occur in internally focusing telephoto zoom lenses. Whether it appears, and how strongly, depends on the optical design. At close distances, this can result in a visibly shorter effective focal length, meaning that the actual magnification is below what the maximum zoom setting would suggest—for example, effectively closer to 300 mm instead of 400 mm.
With the Sony FE 400–800 mm F6.3–8 G OSS, Sony has already shown that this issue is being addressed in modern super-telephoto zoom lenses. Sony promotes the lens with reduced focus breathing for improved video recording. In addition, Sony’s digital Breathing Compensation mode can counteract the effect with compatible camera and lens combinations. Whether a possible new 100–400 mm f/4.5 GM would be designed similarly remains to be seen.
The Compromise: Why an f/4.5 Aperture?
While early discussions in forums speculated about a constant f/4.0 aperture, current rumors point to a constant f/4.5 aperture.
From a technical perspective, this would be a pragmatic design decision. An f/4.0 aperture on an internal 100–400 mm zoom would require a large front lens diameter. That would not only make the lens huge and heavy, but also significantly pricier. The f/4.5 aperture would therefore represent a compromise between light-gathering capability and physical dimensions.
Price Expectations in the High-End Segment
Sony’s G Master technology comes at a price. Although reliable information is still lacking, estimates for the new telephoto zoom range between $5,000 and just over $5,500.
Successor to the 100–400 mm GM (GM II) or an entirely new product line?
So far, it is also unclear whether the rumored telephoto lens would actually be the direct successor to the current model—a classic “GM II”—or whether Sony is introducing an entirely new product line. From my perspective, there is a strong case for a new line. The standout advantages of the existing Sony FE 100–400mm GM, aside from its strong sharpness and autofocus performance, are primarily its compact size and very low weight. A new, massive model with an internal zoom would completely abandon these characteristics. That suggests the new internal-zoom 100–400mm GM could be positioned more as a standalone addition for specific requirements, while the current, lighter model will hopefully remain in the lineup as a more portable alternative.
Contextualizing the Rumors
The current speculation is primarily based on leaks from How2fly, as well as reports from SonyAlphaRumors and PhotoRumors, which have also been covered in Germany by outlets such as Photografix. So far, the only officially confirmed detail is Sony’s “Alpha In Residence” event on May 14/15, 2026. The FE 100–400mm f/4.5 GM has not yet been officially announced by Sony.
