Magnetic CPL filters comparison: Freewell ›vs‹ Kase ›vs‹ K&F Concept ›vs‹ Haida ›vs‹ VFFoto – Optical Quality & Usability
Comparison of optical quality and usability of magnetic systems with polarizing filters (CPL) and magnetic caps.
This usability test was to evaluate how firmly the magnetic systems hold the filters and how natural it is to change them.
Freewell, Kase, Haida and K&F Concept tested on 82 mm. VFFoto on 49 mm as a bonus from my older camera.
TL;DR Abstract
Optical quality is similar, with just VFFoto having a slightly more notable color tint.
Freewell and Kase outperform the others in usability, with Freewell having a slight edge. VFFoto was significantly worse on 49 mm.
Quality comparison
All filters are optically good. Only VFFoto has a slightly notable color shift.
Color stability
There's no significant difference in the color shift. All filters are ±500 K warmer. VFFoto is the only one with a slightly notable color shift. Note that the VFFoto was on Rx1rII, so do not compare it directly with others on A7rV.
Resolution
There's no significant difference in resolution.
Light transmission
There's no difference in the pure white scene with ambient lightning. All filters lost 1 stop, except for VFFoto.
Interestingly, Freewell was 0.1 stop darker in real life scenes (consistently across 3 shots), but it had the same intensity in the following white scene in ambient lightning.
Temperature is rounded to hundreds, EVs to one decimal. Slighter changes are observable in the raws if anyone is interested. EV calculations take into account a slightly higher ISO on the Rx1rII (that lacks a stabilizer).
Raws of ambient light white scene.
Flare
No significant flare was added on top of the lens flare except for the very direct view right into the bright sun in the middle, where it was roughly the same across the filters. VFFoto had slightly more flare in that condition, but that could be because it was on a different lens. But nothing severe.
Note that VFFoto was the only one on the Rx1rII vs. Sony A7rV.
Usability: Freewell best, followed by Kase
Firmness
Freewell and Kase are significantly better than the others. To demonstrate the difference, the cap and filter holds firm enough to pull a camera by it.
Freewell has the best-balanced magnetic system. Firm enough and well balanced across the filter and the cap. Natural to use.
Kase is very close. Its cap is actually even stronger, but that made me occasionally remove the filter together with the cap unintentionally. That increases the risk of dropping the filter on the go. You can probably get used to it, but unlike the Freewell, it’s necessary to think about how to pick it.
K&F Concept and Haida are weaker. To demonstrate it, it got removed when pulling a camera by the cap with the filter on. Only the cap without the filter survived the 'pull test'. Haida is even slightly weaker. None of them fell off accidentally when I was testing them walking in the city, but the risk is higher in more exposed conditions like on a trail or when not attached properly.
VFFoto (49 mm) is quite weak. It might even be worse because of my 49mm version, but it clearly performed the worst. I've been using it for years and I find it constantly being accidentally removed in my bag on my older Sony Rx1rII.
Kase cap is dust collector
The Kase cap has a 'velvet' inside. It looks like a nice touch at first, but it attracts dust as hell. Unlike the similar coating on lens hoods, it does not add any value to the cap, so I consider it a drawback. It attracts the dust much more than similar coatings on the lens hood, probably because it's more hairy.
Haida has a similar 'velvet' as well, but it's not that fluffy, so not a big deal there.
Size: Freewell is thinner
Freewell is significantly shallower than the others. I like it because it’s like it wouldn’t even be on, but it has drawbacks as well. When separated from the lens, a nail must be used to remove the filter from the cap, because there's not much surface to hold it. They have have just a single rim instead of a standard filter thread. That's enough to hold a stock lens cap (tested on Sony), but you can't mount non-magnetic filters (if you still need them).
Unsolved problem: hardly removable with lens hood
None of the systems solves the common problem that it is almost impossible to remove the filter or the cap when a lens hood is on. There's nothing to pick it by, except for a chirurgical 'operation' by a nail. To remove the cap by the nail is hardly possible, and the filter alone almost impossible.
As a workaround, I stick a string to the cap to pick and remove it. Works pretty well for the cap. I’m still figuring out how to glue a similar thread to the filter as well. Work in progress…
Raw photos
Download raws from real-life scene or ambient light white scene.
The filters
All filters were from the top (nano/pro) lines (when manufacturer offers cheaper alternatives).
- Freewell Magnetic CPL Filter 82 mm + cap: €118
- Kase Round Magnetic CPL Polarizing Filter 82 mm + cap: €146
- K&F Concept Magnetic NANO-X CPL CPL Filter — green coated 82 mm with cap: €86
- Haida CPL NanoPro Magnetic 82 mm + cap: €125
- VFFoto Magnetic CPL Nano 49 mm + front & back cap: €124
On top of the filters, I'm using a magnetic back cap together with a second magnetic front cap not to need to bother with filter cases and have the simplest possible setup on the go.
All photos were taken at 45° from the sun with a fixed daylight white balance, ISO 100 and F8 in aperture priority. Rx1rII set a slightly higher ISO because it has no stabilizer. Unmodified raws out of the camera exported from Sony Imaging Edge. Only the ambient white scene exposure was aligned across cameras.
The only reason for the VFFoto being on 49 mm was that I already had it. It actually inspired this test, because I wasn't satisfied with its performance and was curious how competition performs to pick the best for a new camera.
Conclusion
There is no significant optical quality difference between the filters except for the slight tint of VFFoto.
Freewell has the best firmness/usability, closely followed by Kase. K&F Concept and Haida are weaker, but probably still usable. VFFoto was tested only on 49 mm and with this diameter it is too weak.
I don't have a proper explanation why the Freewell was 0.1 stop darker in the real life scene when no such trait was observed on the white scene with ambient lightning. Please comment it if you have an explanation.
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