This could almost be in a new thread. However, the subject did come up here.
I shoot most of the time with no filter at all in either my 760c or my 720x.
I put the IR-only filter in the 760c when the sun angle is low and the IR light becomes an issue. I rarely ever put in the AA/IR filter.
Since I use the 720x for flashless shooting indoors, there's no need for the IR filter at all. I don't need the AA/IR filter as color aliasing never seems to be a problem for the subjects I use this camera for.
Now, I most always have the AA/IR filter in my 560 since I use that one in the studio for shooting printed textiles. Since the shots take up most of the image area, and I'm using studio strobes, the weave of many textiles produces serious color aliasing. So, the AA/IR filter is most useful.
You don't want to use the AA/IR filter unless you really need it, though. It does soften the image quite a bit.
This is, for me, the main feature of these old cameras - that you get to pick the filter you desire (or no filter at all) based on your shooting needs. Plus, the worry about scratching the soft Lithium Niobate filter surface is taken out of the equation - you remove it first. Plus, even if you had a minor scratch, it doesn't show up in the image - it's not mounted at the focal plane like every other design!
The Kodak filter nomenclature is confusing, though. There are three types of filters in two styles for these cameras.
The styles are, of course, for the Nikon F5 body and the Canon EOS-1N body. They don't interchange.
The types are IR blocking only, and a combination of Anti-Aliasing *and* IR-blocking. Kodak referred to them as IR-filters and AA-filters. This has always been confusing, so I tend to refer to the AA filter as an AA/IR filter as they do, indeed, perform both functions. I refer to the IR filter as the IR-only filter to avoid confusion.
The AA/IR filter types are further broken down into one for the 2 MP sensor and one for the 6 MP sensor. This is because the diffusion pattern is different to match up with the different size pixels for the two sensors.
You can use a Nikon style 2 MP AA/IR filter on any of the 2 MP Nikon F5 Kodaks, and any of the 6 MP AA/IR filtes on any of the 6 MP units. Meaning, the one from the 620 works thru the 720x and vice-versa and the same is true for the filter from the 660 and the 760.
There's no sensor size 'gotcha' associated with the IR-only filter since it is a smooth sheet of Lithium Niobate without a diffusion pattern. All you need to have is the style of filter that fits your body.
There were different Kodak part numbers for all the filters as the models progressed. This further confused the issue, of course. The worst part was that it made folks think that an AA/IR filter from a 660 would not work on the 760.
This, I think, was on purpose. Kodak included the AA/IR filter stock with the 660, with the IR-only filter being optional. To help them reduce the price tag on the 760, they included the IR-only filter and had the AA/IR as the option. They wanted to sell new filters for 760's and not have folks keep a filter from a 660 when upgrading.
I have a complete set of Kodak filters for both the Canon and Nikon bodied DCS units. The IR-only filter for the Canon body was the hardest to come by. I finally had to buy a spare 520 that I really did not want, just to get the IR-only filter to use with my 560. Then, a few months later I relegated the 560 to the studio when I picked up a 760c to replace it. So the 560 had to have the AA/IR filter installed and the IR-only sits on the shelf!
This means I doubt that I'll ever use the now way overpriced Canon IR-only filter again. Oh, and you know how all this all works, too. I paid less for the 760c than I did for the 520 I'll never actually use but bought only for the filter that was in it!
Oh, well. I have a 520 that might one day have to serve as spare parts for the 560.