Oppo Find X9 Pro and the big camera marketing fail: How misleading advertising promises the impossible
Oppo has just confirmed that the Find X9 Pro flagship camera will also get a global launch. The smartphone is set to impress customers with its 200 MP periscope telephoto camera with Hasselblad branding and a 1/1.56-inch sensor.
This telephoto camera features a 35mm equivalent focal length of 70mm and an aperture of f/2.1. For those who want even more reach, Oppo offers an optional telephoto converter that effectively increases the focal length of the periscope telephoto camera to 230mm (35mm equivalent), giving the smartphone 10x optical zoom.
As our detailed camera comparison shows, this definitely leads to more detailed photos in daylight. However, Oppo's marketing is misleading because, both on the product page and in the official review guide, Oppo states that the telephoto converter transforms the telephoto camera of the Oppo Find X9 Pro into a 230 mm f/2.1 camera.
However, this is not possible because this telephoto converter is screwed in front of the existing lens of the telephoto camera. The diameter of the aperture therefore remains unchanged at around 6.85 millimeters, but the focal length is extended by a factor of 3.28. While the telephoto camera has an aperture of f/2.1 without the converter, this shrinks to f/6.9 with the telephoto converter.
Drastic loss of light in theory and practice
Mathematically speaking, the actual focal length of 14.4 mm is no longer divided by 2.1 to arrive at the diameter of the aperture. Instead, the focal length increases to 47.3 mm, but the aperture diameter remains at 6.85 mm, so the focal length must be divided by 6.9, meaning the aperture is f/6.9. The figures were extrapolated from Oppos technical data and may vary slightly, but this does not change the premise.
The formula is as follows:
f/k = d (f = focal length, k = aperture number, d = diameter of the aperture)
Without a teleconverter:
14.4/2.1 = 6.85, simplified to f/2.1
With a teleconverter:
47.3/6.9 = 6.85, or simplified to f/6.9
In practice, this means a huge loss of light, as our comparison images show. In the image embedded below, a shutter speed of 1/1.962s is sufficient without a teleconverter. With a teleconverter, the shutter speed increases to 1/359s for the same exposure, even with the same sensor light sensitivity (ISO 50). In this example, users lose around 2.5 f-stops of light when using the teleconverter. Hence, using a teleconverter is not recommended, especially in very low light.
Camera manufacturers show what honest marketing looks like
Camera manufacturers such as Canon demonstrate that marketing can also be more honest. When it comes to teleconverters for system cameras, they generally explain and clearly specify how the converter affects the focal length and aperture of a lens. For example, a 70 mm f/2.8 lens becomes a 98 mm f/4 lens with a 1.4x teleconverter, but a 140 mm f/5.6 lens with a 2x converter. So for twofold zoom, you lose two full f-stops of light.
Other manufacturers simply sweep the problem under the rug. Vivo, for example simply does not provide any information about the aperture on the product page of its in-house telephoto converter, and third-party lens suppliers Moment and Fotorgear, the manufacturer of the camera kit for the Nubia Z70 Ultra, also refrain from providing such information. However, since Oppo explicitly advertises an aperture that is far too large, this is clearly misleading marketing if not outright deception of customers.
