Canon RF 100-400mm f/5.6-8 IS USM

Pros

• Excellent value for the price, often cited as the best budget telephoto for the RF system.
• Remarkably lightweight and compact, making it ideal for travel and handheld use.
• Fast and capable autofocus that can handle challenging subjects like dragonflies.
• Sharpness is generally good, often outperforming older EF-mount equivalents.
• Effective image stabilization (IS) helps compensate for the slower aperture.

Cons

• Slow maximum aperture (f/8 at 400mm) limits performance in low light or indoors.
• Image quality can become soft at the 400mm focal length.
• Performance degrades significantly in overcast or rainy conditions, resulting in high ISO noise.
• Reported issues with image quality degradation when using UV filters.
• Mixed reports on 'keeper rates' for wildlife, with some users finding it limiting as they advance.

Caveats

• Stopping down to f/9 or f/10 may be required to achieve maximum sharpness at the 400mm end.
• Beginners may find the lens challenging to master during the first few weeks of use.
• Some users have noted minor blooming in certain high-contrast shots.

Best for

• Budget-conscious wildlife and bird photographers.
• Outdoor daytime sports and nature photography.
• Travelers who need a long reach without the bulk of a professional L-series lens.
• Users of APS-C bodies like the R50 or R7 looking for extra effective reach.

Avoid if

• You primarily shoot indoor events or low-light sports.
• You require professional-grade bokeh and background rendering.
• You frequently shoot in poor weather or heavily shaded environments.