[LewisM]

Out imaging M83 last night with the FSQ85 and OSC CCD. Focused before the run (Bahtinov magnified 400% and checked at 100%). Rechecked focus every hour (no shift - well acclimated). 600 sec subs.

Irrespective of this each sub seems to have large stars (perfectly round as tracking was sub-arcsec with no deviation and timed at 4 sec exposures) and halos. Detail in M83 is pretty sharp given the seeing. Oddly, each bright star also has a diffraction spike at 5 & 11 o’clock- checking shows no spiderwebs, no anomalies (I had a custom baffle made that eliminated the tiny spacer spikes).

Additionally, I was only using a uv/ir filter as I don’t use LP filters anymore. The subs upon debayer are VERY green (usually just a hint of green).

The temp dropped to 5.7 deg during the entire 3 hrs on M83. Severe vignette in the subs.

Does this sound possibly like a frosted CCD cover glass? (I baked the desiccant last week) or possibly frost/dew on my UV/IR filter? I checked the objective for frost, dew and foreign objects last night and this morning and all clear. Nothing obvious on ccd or filters either.

Considering to add a dew strip to the ccd nosepiece anyway but does this sound like ice/frost? CCD was running at -15 (my set point). I don’t think atmospheric ice.