IR-FILTER (BANDPASS-FILTER) REPLACEMENT: .
Given your IR-Filter is irreversibly damaged by Scratches to a point where you cant Avoid Replacement or just Want To Replace it anyways.
Genuine Replacement IR-Filters are Available directly From Krontech. Its Still not yet available via their Shop, but if you ask them, they will usually sell you one. By now its apparently somewhat normal to just order a Spare Filter when Buying the Camera. Back when i did order mine, i must have been one of the First ones to ever ask about getting a Spare as you could really tell People at Krontech where Quite surprised about that Request.
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Filter Dimensions of the Original Factory Filter installed in my Camera are 0,995mm x 23,98mm x 15,99mm.
Thickness has been Verified by a 0,995mm Gauge Block, but nominal Size should be 1 x 24 x 16mm.
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Now since from what i Remember Shipping, Taxes, and Customs Processing for just ordering a Single filter on its own to Germany are vastly More Expensive than the Actual Filter itself, there are some Alternatives as to where to get Filters from.
Also you might want to run the Camera for Full-Spectrum Use or capture IR-Light / UV-Light only and not mess with your Backfocal Distance (while fairly easily Adjustable on this Camera it can still be a Pain, if you need to Switch a lot back and fourth between them).
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Alternative Sources for Custom Filters include Kolari Vision for US and Schott / Edmund Optics for Europe (but i think they operate worldwide also?).
Kolari Vision confirmed, that they will Cut Filters to Custom Sizes, and the Size Required for the Chronos is Available.
Schott Surprisingly enough also Sells to people privately without having a Company themselves, but have a 1000€ Minimum Order Value in Place (Which probably is a bit Steep for the Average User, unless you want a bunch of Spares for Your Chronos Ring Setup?).
Schott However sells all their Products through Edmund Optics for anyone with super-Small Order Sizes like Single Units of Custom Size Filters. And Yes, they also Cut to Custom Size, and the Required Size for the Chronos is Available there.
Then there is also Stuff Like this here, but i cant say anything about the Quality of the Filters they Sell or the Quality of their cuts, as i never bought there, try at your own risk:
https://www.ebay.de/itm/192884462869 If nothing else works, or you are in some really Remote Place/ Country, your best bet on finding a Replacement would Probably be to find some Store / Shop that does Full-Spectrum Conversions of DSLRs and such, they usually have Filters at hand and Tools to cut them to size Properly.
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Generally you can also just get whatever 1mm thick IR-/UV-Cut Filter Glass and Attempt to cut it at home, if you want to go as cheap as Possible:
https://picsngeek.at/photography/cutting-filter-glass-for-camera-ir-or-full-spectrum-modification/ But i generally do not recommend, especially the way its done here in this Guide. Apart from a bunch of things i would probably do different, Applying Any kind of Adhesive Tape is Strongly Recommended against, as it can damage the Coatings on the Filter or straight up rip parts of it clean off, as well as possibly leaving Residue on there.
However, if you Really need to, and dont have access to anything better, its probably still Resulting in a better looking Image than when used without one and all the Pink Taint from the IR Light on there. So more of an Emergency "Live-Hack" kind of thing than anything else.
Note that most Circular IR-/UV-Cut Filters (The ones you Screw onto your Lenses in the Front) are thicker than 1mm (something like 1,4mm Thick is Common for the Somewhat larger ones, if i recall Correctly), which will mess with your Backfocus Setting/ Distance and maybe will lead to issues when Screwing the Bracket back in on the Chronos, that is holding the Filter (Be very Careful not to over-Tension it, risk of Cracking it!), but again, if you have one of these Circular ones on hand and need one RIGHT NOW in an Emergency, it can Work.