Today’s Question: Instead of buying an expensive super telephoto zoom lens, I would rather buy an extender for my 70-200 zoom lens. Canon charges the same price for its 1.4x (https://bhpho.to/3oaT4Tm) and 2x (https://bhpho.to/3bnaxQv) extenders. Are there any downsides picking the 2x extender over the 1.4x extender?
Tim’s Quick Answer: The key difference between these two extenders is that the 2x will cause you to lose one additional stop of light. This obviously affects potential shutter speeds in addition to degrading autofocus performance.
More Detail: An extender is effectively a magnifier for your lens. These extenders are often available in a 1.4x and 2x strength for different lens mounts for different camera makes. With a 1.4x extender you will lose one stop of light, and with a 2x extender you will lose two stops of light.
With less light available when using the 2x extender, you would obviously need to compensate with exposure settings. That can lead to a slower shutter speed, which can be problematic depending on the specific circumstances. In addition, that loss of light will reduce autofocus performance, which can be a real hindrance.
Of course, there is also the additional magnification to consider. With a 70-200mm lens, for example, the 200mm focal length would translate to an effective 280mm focal length with the 1.4x extender, but a 400mm effective focal length with the 2x.
Therefore, when considering an extender my view is that the 2x option makes the most sense, as long as you can manage the loss of an additional stop of light.
In a general sense it is also important to confirm compatibility with the specific lens you intend to use with the extender. Many extenders only support prime lenses, plus a handful of zoom lenses (as is the case with the Canon extenders). With some configurations you may lose autofocus altogether, or you may be limited as to which focus points are available.