UV/IR needed? [Deep Sky] Acquisition techniques · Tony Gondola · ... · 29 · 892 · 3

Tony Gondola:
I am wondering about the common wisdom of always using a UV/IR cut filter if shooting broadband OSC. I can understand its use with refractors that might not be well corrected at the extremes of a cameras sensitivity range but why do it with a reflector which brings all wavelengths to the same focus. I can see that it would effect having a "natural color balance" whatever that means these days but wouldn't it be better to get as much signal as the sensor can detect?

Many tubes are dark in visible but very reflective in IR.

Tony Gondola:
I finally had an opportunity last night to do a side by side filter test of M81. Both images are stacks of 160, 15 sec. subs with full calibration. Each image was color balanced, stretched 10%, background extracted and noise reduced. The no filter image was taken before meridian passage and the uv/ir image after to match elevation Transparency and seeing seemed to be constant throughout the session. Sensor was a ZWO 585 cooled to -10c, gain set to 255. Telescope was a 150mm f/6 Newtonian with standard coatings, no corrector configuration. The uv/ir cut filter is from SVBony. Average measured FWHM for both images was 2.8". Imaging scale was 0.66 arc/sec per pixel. Light pollution, Bortle-7.5



It should be noted that the flats had to be shot at 0.05 for the uv/ir cut and 0.02 sec. for the no filter config to get a similar histogram between the two configurations.