On my short tube achromats I usually employ a Baader Fringe Killer/Neodymium stack for occasional planetary observing. However, there are times of dodgy transparency when I can use the Fringe Killer stacked with a more conventional contrast filter. If I want even more contrast I sometimes use a Wratten #8 Light Yellow or even occasionally a Wratten #11 Yellow-Green filter. These are traditional minus cyan choices for achromats apparently. I tend to stack the yellow filter in the diagonal nosepiece with the contrast filter behind it in the light train. This is either as a directly connected stack in the nosepiece, or just the contrast filter is threaded into the eyepiece, leaving the yellow filter in the diagonal. After a few nights of observing Jupiter near transit with my ST80 during predominantly deep sky sessions, I noticed that the Baader FK/Neodymium stack didn’t always give me the contrast I wanted. This May has had some nice days but there seems to be a dampness in the night air which isn’t helping the transparency (or my recently developed cough). I normally use a Wratten #8 stacked with the Baader Neodymium, or if I want even more contrast, the #8 can be stacked with a TS Optics UCF1 contrast filter. I believed that as the UCF1 could be a little too aggressive for Jupiter’s nuances in this weather a happy medium between the Baader Neodymium and the UCF1 could be found. As far as I can determine 'Solomark' is a trademark of Yuyao Qihang Optical Instrument Co., Ltd. Yuyao City, Zhejiang Province, China. The Solomark Crystalview Moon Filter and Solomark Light Pollution Filters are roughly a third more expensive than the Solomark Moon & Skyglow filter. The latter was about £10 (Sterling) which itself is a fifth the retail price of a Baader Neodymium. I believe these filters are also marketed as Gosky. Naturally I tried all of these both in daytime tests and nocturnally. I then discovered something a bit odd. In extremely sophisticated and scientific daylight trials (entailing holding the stacked filters up to a partially closed Venetian blind in bright daylight lol) the stacked #8 and Solomark Crystalview Moon and Solomark Light Pollution Filters produced definite reflective double images. These images were virtually ghosts of the observed light source, almost as if they were reflected from one of the glass filter surfaces. The Baader FK and Neodymium didn’t produce these reflections. The TSUCF1 contrast filter didn’t produce these reflections either (in any combination). Neither did the cheapest of the filters; the Solomark Moon & Skyglow filter! I have no explanation for this. I can only assume the Solomark Crystalview Moon Filter and Solomark Light Pollution Filters don’t have effective anti-reflection coatings, if any. I’ve ordered an OVL Light Pollution filter to compare it with the Solomark. I’m curious as to how it will fare in the ‘Venetian blind’ test. Watch this space.