Kevin_A Let me know how yours turns out and I will post when the skies clear!
Not a chance my skies will clear before yours :-). (Yeah, it is raining at the moment.)
I don't take the covers off my mount when there is a chance of rain, :-).
By the way, I have an NBZ-II coming my way next week. I also have a 365nm LED flashlight that I can subjectively test to see how good various UV-IR blocks are. When the NBZ-II appears, I will parade my dozen or so filters that claim to block UV.
Not a great way to measure (the center wavelength of that LED can be 10nm off). I don't have a good white light source for my spectrometer, unfortunately; and most cheap (less than $20,000) spectrometers cannot measure the blocking aspect to the dynamic range that just measuring the max ADU of a frame with a flashlight in it, anyway).
But at least I will be able to tell what blocking filters actually blocks UV, and which are bogus. A quick test in the past has shown the ZWO UV-IR block to be placebo - caveat emptor; but I should be able to compare it with other filters next week. I had kept it around just for such an occasion.
UV will excite the blue channel of a sensor, and will look blue in an image, even though it is way past violet. Without a controlled experiment, it is not easy for an unsuspecting customer to buy a UV-IR cut that is placebo (well, not placebo in terms of losing money). 365 nm should be past the point where a decent UV cut filter should work, so any significant energy that is passed to the camera sensor at 365 nm will indicate a moderately poor UV-cut filter (thus giving blue fringes around stars from an OTA that whose spot diagram bloats in the blue side of the spectrum).
This collection of spot diagrams is from a Cloudy Night posting. Notice the blue bloat from an Askar even at the optical axis (0.00mm). The spot diagrams may not be scaled properly, but you can see the blue bloat clearly on the Askar.
We'll see how my simple tests will turn out. I bought the flashlight a couple of years ago to use for bonding the UV-sensitive epoxy (like the kind used by dentists today). Have to find my UV blocking goggles too :-).
BTW, ZWO swears up and down that their color ASI2600MC uses an UV-IR cut window (see the last few posts in the following foum thread - some very recent). I happen to also have a pristine (never opened) ZWO D60 IR-CUT filter for just such an occasion. We'll see if the 60mm glass window is as poor as ZWO's 2" mounted filter. If it is poor, it is time we expose some of the marketing nonsense. The curve is from a Agena page -- notice that they claim a brickwall at 400 nm, we'll see if even a cheap Optolong UV-IR cut beats it.
https://bbs.zwoastro.com/d/13239-asi2600mc-protective-window/5
They also do have an AR version of the 60mm, and I might have installed it in my ASI2600MC. So, using an external D60 glass is the only sure way to measure the window.
Chen
