I have a QHY 5III290C, a QHY 5LIIM, and a QHY174M cooled camera. I also have a Orion SSAIO camera which is a clone of the QHY5LIIC, but incompatible with QHY's software. (But at least it got me to get me to use more modern camera . than my Meade Pro II) I have been very happy with these cameras and can play with mono, color, and different pixel pitch configurations using them without busting the bank.
The problem I have is that I am confused about the window/filters that came with my cameras. They are all adaptors for CS, and are needed to keep the CCD clean and accept extenders for 1 1/4 focusers. It looks like from the QHY documentation that the filters are AR+AR. This would make me think there is no IR filtering. I bought a IR cutoff filter for the cooled QHY174M as it seem clear that a IR cutoff is needed for that camera. The other "CS" adaptor/AR windows clearly have an AR filter on them, but I am not sure they have any IR reduction.
As an experiment, I have a TV remote that has an IR led where you can see the LED itself, rather than having a plastic IR filter over it and are not always as far IR. Since it is IR LED is very invisible, it must have a wavelength longer than 780 nm, and maybe 830 nm. Anyway, using the cameras, I can easily see the blinking remote without any filters. With the IR cutoff filter, the IR is definitely attenuated. The filter on the Orion adaptor (labeled C and claimed by Orion. to be an IR filter) transmitted significantly more IR than the cutoff filter. However, when I checked the window/filters on the QHY 5LIIM or the QHY 5III290C, the also both attenuate the IR, but slightly less than the Orion filter.
The question is do I need a separate cutoff filters for the QHY5II and QHY5III cameras if I use them for anything other than guiding? I occasionally used them for planets and easy deepsky imaging.
Thanks for any help.