Back onto the photometry thread, similar to what I mentioned previously about SCT corrector plates being next to useless for UV measurements, the spectral response actually applies to all components in your optical train not just the correct plate. Don't get me wrong, you can still use a SCT, but you'd need a way of cross checking the accuracy of the measurements. Perhaps using some offset data from other well known sources.
I know you're still learning to crawl before you walk, but considering you're testing CCD and CMOS chips that would be suitable for photometry, I thought I'd also provide more info on the spectral response.
Typically a CCD or CMOS chip chamber is covered using a type of glass (called a window). I recommend during your testing of cameras that you investigate the glass type the manufacture is using. Normally Schott BK7 is used. It has a reasonable reponse to UV wavelengths, but not the best. You should try to obtain a camera that uses MgF2 (Magnesium Fluroide) as this glass allows wavelengths all the way down to 120nm - well below the start of the visual wavelengths. This is not a major issue as typical U filter only starts at 300nm, but you want to make sure the camera is still sensitive lower than 300nm so no cut-off is experienced. Most glasses will transmit all the way up to 1200nm - IR (700-1200nm) wavelengths. UV is probably the most critical and hardest to reach depending on telescope design.
Obviously, having a camera that allows you to go low into the wavelength spectrum wont make a difference if there is poor spectral response in other areas of the optical train. Hence the reason why I indicated you need to look at the big picture, not just the camera.
This in turn will send you on a quest to determine what is the most optimal design/telescope for photometry. I haven't found this yet - but if you do come across it, please let me know. Generally, you can use most types though I read that well corrected refractors are good. Many are corrected down to 360nm. I have not looked into mirror based designs to make any comment.
Finally, the speed of the optical system is not really a big issue with the UBVRI filters as they are not really that narrow. Compared to a 3nm or 6nm Halpha filter they are quite broad. Using a fast instrument such F/2.8 or F/4 camera lens, the light cone that hits a narrowband filter can actually shift the spectral response. So instead of the Ha filter being centered at 656.3nm, it shifts. This results in missing the critical narrow light path of the filter and delivers a poor Ha image. This is the reason why if you have a fast optical system, its best to stay away from really narrowband filters. Its best to go for 10nm or higher so when the shift occurs, the filter will still transmit at wavelength. Alas, you don't have to worry about this with the UBVRI filters.
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