Buy 49mm. On a Leica Q3 that is the factory thread. On a Fuji X100 / X100V / X100VI you need the adapter first, then the same 49mm mouth. After the size is right, pick one job: everyday protection, or a mild 1/4 black mist you can leave on. A CPL is not the first filter on either of these bodies.

I'm Leo Liang. I run XT Filters. My daily body is a Panasonic GH7 with the OM System 12-40mm f/2.8 PRO II — not a Q3 or an X100 — so I will not pretend I have logged frames on those two. What I can do is sort the thread sizes we keep answering in the shop, and the two first-buy paths that make sense once the mouth is 49mm.

Both cameras end at 49mm — one of them needs homework

The Leica Q3 43 prints "43" for focal length, not for the filter ring. The filter thread is E49 / 49mm. We already walked that trap in Leica Q3 43 filter size is 49mm. Order 49mm; order 43mm and the ring will not mount.

The X100 family has no native filter thread. You take off the trim ring, mount Fuji's dedicated adapter (or a compatible one), and the working mouth becomes 49mm. That sequence is in Fuji X100 filter thread is 49mm. Without the adapter you are shopping air. Do not chase 39mm for these two bodies — that size belongs to other mouths (XF pancakes, some Leica lenses), and it is the wrong answer here.

One Q3 clearance note: the factory square hood and the macro focus range leave less room than a bare thread. Treat hood-plus-macro as a check on your own copy. We do not claim our dedicated 49mm Q3 cut keeps the factory hood and macro together — that combination sits outside what we have verified.

Protection first, or mild mist first

Once the thread is 49mm, the "first filter" question is about job, not brand mythology.

Everyday protection. If the camera leaves the house a lot — bag rubs, fingerprints, salt spray, forgetting the cap — a coated clear / UV protector is the boring, correct first buy. It takes scratches and film so the front element does not. On my own GH7 kit I have kept an XT996S on the 12-40 PRO II since March 2025. No visible image-quality loss. Evening seaside, it catches the salt haze instead of the glass. The lens rubs the bag; some days I forget the cap; with the filter on I stop worrying about the front element. That habit is why I still push protection as the default first ring for a fixed-lens walkaround camera.

For the Q3 and adapted X100, the card on this post is the XT996 PRO Black Frame in 49mm — the cut we stock for these mouths. Specs that matter: average transmission ≈99.6%, so exposure does not move in practice; average reflectance ≈0.08% with a double-sided 36–48 layer multi-coating, so bright sources bounce less than a weaker clear ring. Dust-, water-, and scratch-resistant build. Shop it as a protector, not a haze filter — on digital the "UV" label is mostly habit.

If you already own a standard 49mm clear protector and the X100 adapter is on, that ring works too. You do not need three SKUs on day one.

Mild look filter. If the camera is mostly for portraits, evening streets, or anything where digital bite bothers you more than grit, start with Black Mist 1/4 — not 1/2, not 1/8 as the first leave-on. The XT888 135 Bottom Black Mist 1/4 is the mild bloom we stock in these 49mm mouths: average transmission ≈88.8% (roughly a stop of light cost — fine as a look filter, not pure protection), average reflectance ≈0.3%, double-sided 28–36 layer coating. It softens specular highlights a notch and takes the hard digital edge off without turning the frame into fog. Leave it on if that is the look you want most days; swap it off when you need a clean protector.

Pick one path. Do not stack protection under mist on day one — two flat surfaces in front of a fixed lens add flare paths you have not measured yet.

Why a CPL waits

A circular polarizer earns its keep on reflections in glass, water, and some foliage. On a Q3 or an X100 the first problem is almost never "I need to kill a window reflection." It is "I need the right millimetre," then either a sacrificial front plate or a mild leave-on look. A CPL also costs light, needs rotation, and is easy to leave at the wrong angle on a pocket camera. Buy it later, after the 49mm mouth and the first job are settled.

Skip ND here entirely. Neither of these bodies is asking for a density filter as the first screw-in.

Who should not buy yet

Skip the filter order if you do not have the X100 adapter in hand — email me and we will sort the sequence before you pay for a ring that cannot mount. Skip a mist-first buy if your main worry is scratches and bag rub; get protection instead. Skip any listing that sells 39mm or 43mm as the Q3 / X100 answer.

Shop 49mm XT996 PRO protection or 49mm XT888 Bottom 1/4 mist. If the X100 adapter is still missing, email Leo and we will get that sorted first.

— Leo Liang