Very good quality K & F Concept ND1000 square filter set consisting of glass filter holders and lens adapters for the filter holder. The package is divided into 3 parts: 1. A bag with metal rings adapters for different lens diameters. 2. A case containing the filter and its leather carrying case. 3. A box with the filter holder. The adapter rings allow us to place the filter holder on any lens as we have a large number of different diameters. They are made of black metal and are well made. With inscription on each ring of the corresponding diameter. The filter is made in Germany glass. It is a 100x100mm square and 2mm thick ND1000 filter. It allows us to remove 10 levels of light to make daylight long exposure photos perfect. In the example photo I've hung, midday is taken at around 30 inches. I love the game that you can get to this filter. The filter comes in a leather case and tissue paper. The case is heavy enough to protect it properly. The glass does not mark easily with fingers and does not attract dust. The filter holder is metallic with the part where the filters come from some kind of very hard plastic. They fit easily on two filters 100x100 and also on the slopes 100x150mm. The attachment system on the adapter ring is thanks to a very handy metal tab. In several tests I ran under different lighting conditions, I didn't notice the ingress of residual light because of the space between the filter and the portafilter. The photographs have a slight magenta tint that is very easy to edit, but they are not overdone at all. With the complete kit and price, it's a fantastic filter to experiment with and get excellent results. I'm really excited and really enjoying it. I highly recommend it!

K&F Concept Square Metal 100mm Filter Holder with 8 Lens Filter Adapter Rings 49mm to 82mm. Great addition to my filter collection. I bought the wrong size filters so I had to buy this kit. Well built product with most of the adapters I needed. K&F seems to be making some really good stuff at a great price that will help us amateur snappers without breaking the bank.

In addition to square filters, I also bought the low-cost magnetic filter holder set. I can only say top. However, I lack the possibility of obtaining ND 8 and ND 64 (magnetic) because only ND 1000 and polarization filters are available. A second glass-filled filter holder is included, which is super durable with adapter ring for a second lens size and yet! fits into the super handy case. For the time being, this low-priced set with magnetic holder is enough for me; for further demands, I will probably switch to another manufacturer's “large” filter holder system (about 400 euros with three ND filters). Which photographer doesn't know this “want to have?” In short: Riko Best's contribution to YT convinced me. Would I recommend it? Yes, anyone who wants to work with grey filters now and then. LG

Among several domestic and foreign companies offering square filters, I decided on this one because it is easy to put on and take off from the lens, it is thin in the front and back, and it comes with a C-PL filter
For C-PL filters, just open the lid and drop in from above. If you make a mistake in front and back, it will not fit.
The square filter has just the right amount of friction and doesn't feel like it's going to fall off.
Almost all metal, except for the four metal adapter rings and C-PL filter, the holder alone weighs 110g.
In terms of design, the overall impression is sophisticated.

up until now, square filter holders from other companies have been expensive, and we have endured with SIOTI holders.
I also had an old K&F holder, but it is difficult to use C-PL.
That's where this product comes in. I bought a set of holder + C-PL + ND1000 for the time being, but it is well thought out. There is no vignetting even at 16mm with the Nikkor16-35mmF4, and there is no annoying color cast.
I'm a little worried about the C-PL's adjustment dial squeaking, but I have no complaints at this price with this content.
After that, I would like to see a frame that can be attached to the existing filters sold on the overseas official site, and a filter case that can hold about 6 to 8 filters with the frame attached.
~Addition~
I purchased a 100x150 frame from the US site of K&F. Existing filters can now be used, and full-scale operation is now possible.

Seems to be properly monitoring the air quality. Also very affordable.

Human sick easy when not good Air. This is perfect indoor monitor for air which you can control ion your house and reset or clean it. it also smart so connect your phone and humidifier so you can control air.

We use this as a proxy for ventilation and air flow in small spaces like doctors treatment rooms or outpatient clinics. I am immunocompromised and must take care of myself. We've tested it at home and driving and you can see how the CO2 level changes with more people or more ventilation. Any CO2 level over 800 is considered the bare minimum of adequate ventilation by environmental engineers according to my reading, but do your own research. I was surprised how little ventilation many places had that I tested, I was breathing a lot of stale air with who knows what bacteria or viruses floating around. Whatever you use it for, it works and you can stuff it in a purse or backpack for travel.