Canon RF 100-400mm f/5.6-8 IS USM vs Canon RF-S 18-45mm f/4.5-6.3 IS STM

Both are Canon RF mount zooms for travel and budget — here's how the specs differ and which to pick. Every spec is from the manufacturer's own catalog.

Last verified 2026-09-01 · Canon RF mount · prices change — check the retailer

Spec	Canon RF 100-400mm f/5.6-8 IS USM	Canon RF-S 18-45mm f/4.5-6.3 IS STM
Focal length	100-400mm	18-45mm
Max aperture	f/5.6-8	f/4.5-6.3
Type	zoom	zoom
Coverage	full-frame	APS-C
Mount	Canon RF	Canon RF

Which should you buy?

the Canon RF-S 18-45mm f/4.5-6.3 IS STM opens wider (f/4.5-6.3) — brighter in low light and more background blur
the Canon RF 100-400mm f/5.6-8 IS USM covers 100-400mm and the Canon RF-S 18-45mm f/4.5-6.3 IS STM covers 18-45mm — pick the range that matches what you shoot
the Canon RF 100-400mm f/5.6-8 IS USM covers full-frame (also works on APS-C bodies); the Canon RF-S 18-45mm f/4.5-6.3 IS STM is APS-C-only — it won't fill a full-frame sensor

Where to buy

Canon RF 100-400mm f/5.6-8 is USM Telephoto Lens

Canon RF 100-400mm f/5.6-8 IS USMSee price on Amazon Amazon has no new-stock listing for this one right now — this button runs an Amazon search for it rather than opening a product page.

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Canon EOS R50 Mirrorless Camera with RF-S18-45mm F4.5-6.3 is STM & RF-S55-210mm F5-7.1 is STM Lenses, 24.2 Megapixel CMO

Canon RF-S 18-45mm f/4.5-6.3 IS STMSee price on Amazon

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FAQ

What's the difference between the Canon RF 100-400mm f/5.6-8 IS USM and the Canon RF-S 18-45mm f/4.5-6.3 IS STM?
The Canon RF 100-400mm f/5.6-8 IS USM is 100-400mm f/5.6-8 zoom, full-frame; the Canon RF-S 18-45mm f/4.5-6.3 IS STM is 18-45mm f/4.5-6.3 zoom, APS-C. Both fit the Canon RF mount.

Which is better in low light, the Canon RF 100-400mm f/5.6-8 IS USM or the Canon RF-S 18-45mm f/4.5-6.3 IS STM?
The Canon RF-S 18-45mm f/4.5-6.3 IS STM — its f/4.5-6.3 maximum aperture lets in more light and gives more background blur than the f/5.6-8 of the other.

Do the Canon RF 100-400mm f/5.6-8 IS USM and Canon RF-S 18-45mm f/4.5-6.3 IS STM fit the same camera?
Yes — both are Canon RF mount lenses, so they fit Canon EOS R series (full-frame R5/R6/R8) and APS-C (R7/R10/R50). Note the Canon RF-S 18-45mm f/4.5-6.3 IS STM is APS-C-only and won't fill a full-frame sensor.

Citing these specs? Go ahead — manufacturer data, last verified 2026-09-01. Copy a ready-made reference:

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Canon RF-S 18-45mm f/4.5-6.3 IS STMAffiliate linkSee price on Amazon