Question 1

Which Canon lenses use a drop-in filter?

Accepted Answer

Canon super-telephoto lenses such as the EF 400mm, 500mm and 600mm f/4 series, as well as certain large-aperture EF lenses, feature a drop-in filter slot at the rear of the lens barrel. These lenses have front elements too large for practical screw-in filters, so the drop-in slot is the only way to use optical filters like a CPL or ND.

Question 2

What does a circular polarising filter actually do?

Accepted Answer

A circular polarising filter blocks light waves vibrating in a specific plane. In practice this means it cuts glare off water and glass, makes blue skies darker and more saturated, and reduces atmospheric haze. Rotating the filter changes the intensity of the effect. Unlike colour adjustments, polarisation cannot be fully replicated in Lightroom or Photoshop.

Question 3

Is there a difference between a drop-in CPL and a standard screw-in CPL?

Accepted Answer

The optical effect is the same — both reduce reflections and boost contrast. The difference is purely mechanical. A screw-in CPL threads onto the front of the lens, while a drop-in CPL slots into a holder inside or at the rear of the lens. On large super-telephoto lenses, a front-mount CPL would need to be enormous and expensive, so the drop-in format is far more practical.

Question 4

Is buying a used Canon drop-in filter safe?

Accepted Answer

Yes, provided the filter glass is free of scratches, chips and delamination — all things to check in the item photos. At 18g and with no electronic components, drop-in filters are mechanically simple and durable. Every used filter on Camera-tweedehands.nl is individually photographed and comes with a minimum 12 months warranty, so you can buy with confidence.

Question 5

Can I use this filter on Canon RF super-telephoto lenses?

Accepted Answer

Canon's RF super-telephoto lenses use a dedicated drop-in filter system that is compatible with Canon's drop-in filter lineup. Check your specific RF lens manual or the filter slot markings to confirm compatibility before purchasing, as Canon offers more than one drop-in filter variant for different lens families.

Question 6

Does a CPL filter affect autofocus or exposure?

Accepted Answer

A circular polarising filter (as opposed to a linear one) is specifically designed to be autofocus-safe — the 'circular' in the name refers to the polarisation type, not the filter shape, and it avoids interfering with phase-detection AF systems. It does reduce light transmission by roughly 1.5 to 2 stops, so your camera will compensate with a slightly slower shutter speed or higher ISO in auto modes.

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Canon Circular Polarising Drop-In Filter A

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About the Canon Circular Polarising Drop-In Filter A

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