So some of you know I do AP as well and use the 224mc as my guide cam. I’ve had great success with it threaded on to my Guidescope with no differential flexure and more than enough SNR even when the seeing was less than ok……until I did something different. Instead of a direct thread on, I attached it using the 1.25 nosepiece slipped in for easier focusing. All of sudden, my SNR was terrible, the star was bloated and there was what appeared to be halos or micro lens reflections to the point where guiding became impossible. Thought it was a camera issue, my software, dust or dirt, etc. Took a break, did a meridian flip and then set the camera back on with a threaded connection as I’d done hundreds of times before and….voila……everything was right in the world again….but why?
While I was catching a few more frames of my target before the zenith spin, I took the removed nosepiece and had a look. With my headlight on and aiming inside the extension so I could inspect, the threaded portion was heavily reflecting light on the cut edges of the threads and with the light off axis, the reflections were localized but more intense. Had about an hour til dawn and I needed to stay up to get my sky flats so I had some leftover peel and stick flock cloth which I carefully cut and applied to the inside threaded portion of the 1.25 nose cone and re installed it on the 224 can preceded to test guiding again……and everything was fine……SNR back to thread connection levels, no halos and no bloat…….Total rms back to .7 or so.
Needless to say, the threaded interior portion of the 1.25 nose cone was causing significant light scatter on bright targets…….and on big and bright Jupiter and Saturn, in can only imagine how much resolution was lost last season while imaging the planets with this configuration. Even though the test was impromptu and crude, the flocking will stay and I’m gonna take a black sharpie to the anodized red surface of the 224mc around the sensor opening as well since it seems to have a protective semi gloss coating over the red anodized finish. Of course, your experience might be different and yet I’m surprised at myself for not recognizing the reflective surfaces sooner. Once Jupiter is at a high enough elevation for imaging, I’ll do some AB testing of flocked and unflocked nose pieces to see if there’s an appreciable improvement. Stay tuned!
