Here I attempt to compare the effect of using filters, each with a different band pass. All images were obtained with a C8 SCT (no Barlow) with a monochrome camera with a IMX 178 sensor (2.4 micron pixel size.) Seeing on this particular evening (24 July) was below average (2/5.)

For the three images, I used (a) and IR/UV blocking filter, (b) a R+IR filter which passes light above 610 nm, and (c) an IR filter which passes light above 742 nm. To make the results as comparable as possible, I had hoped to use the same camera settings in each case. Unfortunately, this just was not feasible, as the IR filter passes far less light than the other two. Instead, I adjusted the gain and frame rate for each filter during acquisition so that the peak in the histogram was at 40%. All three images sets were obtained within the same 15 minute time period, and seeing appeared to be relatively stable between each aquisition.

Post-processing for each image was kept as consistent as possible. For each filter, three video captures were obtained, and the best 1000 frames from each were stacked. These images were then sharpened in Registax (using the same settings for each) and de-rotated using WinJuPos. I used NeatImage to reduce noise and performed a final sharpening in Registax.

In any case, I performed this test for my own benefit, mainly because I enjoy planetary imaging but seeing conditions are often sub-optimal in my location. I wanted to see to what extent filters could help. Based on this comparison, the IR long pass filter seems to provide better contrast and overall a sharper result. A higher gain setting is required to acquire acceptable signal, however, so the trade-off seems to be higher noise present in the final image. An R+IR filter may be a good compromise for dimmer targets.

As a final note, the shadow of Europa can be seen on the cloud tops of Jupiter in each image.