Reflection Nebulae in Summer

End of June 2025 we had some clear nights during new moon, but there were no suitable DSOs visible from my location. So I simply decided to do an experiment with the reflection nebula SH2-73. This should be no simple target from my Bortle 5 sky and the missing astronomical darknes does not help either.

But my intention wasn't about to check if I can image this target at all, rather to see the results from two totally different setups running in parallel. So I mounted the monochrome image train to my 100mm f/5.8 (580mm focal length) APO and the OSC to my fast 130mm f/2.8 (360mm focal length) Hypergraph.

I somehow expected to see better results from the faster telescope, but after collecting some hours of luminance I had to realize, that this won't be the case.

ASI2600MC, 360mm f/2.8, 11.5h

In fact the results with about 12 hours integration time each were pretty similar. Of course this is a pretty special case and the slower telescope had a big advantage in collecting pure luminance data. If I would have taken just RGB with the monochrome setup, the faster telescope, for sure, would have won.

Comparing the raw data I observed a slightly different overall tint, even after spectrophotographic color calibration (SPCC) in Pixinsight. I tried to match both for the nebulous parts, but this did not work well for the stars. The cause is probably the bayer mask with its overlapping filter bands and that I did not use an UV/IR cut filter with the OSC.

In addition the image taken with the monochrome setup exposes more of the finer structures and background galaxies.

Using the slider the differences can be explored quite easy: