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Thanks for the effort, guys! I only have a moment this morning, so just the basic answers. Image was acquired with: 6" RC + AP ccdt67 reducer, at 993mm f/l QHY183C - note this camera has a UV/IR-cut window, so no additional filter was used pre-process in Siril, stacking with No Normalization Flats -...

M13 is one of those objects where (I think!) there is a definitively correct color palette. For example, the image at https://science.nasa.gov/colors-and-magnitudes-m13 shows a mix of blue and reddish, along with spectral data supporting that. In my own M13 image: M13_g5o8_-10c_631x30s_90pct_sigma1....

I'm back with a variation on the same question.

Same telescope - RC6 with AP CCDTV67 reducer. I rearranged the optical train a bit, and wound up maybe a mm short compared to the spacing I had been using. The plate-solved focal length previously had been 877mm, last night was 894mm. OK to combine?

I'll take "all in all a respectable image", and be happy.
I did use a bit of walking noise reduction. I still see some patterning at a 45° angle in the image, but maybe that's just over-active human pattern recognition.

Here's what I got as a first go. Looks like cranked-up aggressive wipe is doing its thing on the part of the stack with frost. Another 8 hours would help bring out the outer arms better, but I suppose that's why some people refuse to do broadband imaging from Bortle 7. A bit of walking noise, too, a...

Thanks, Ivo. I obviously should have shot a special set of flats with the frost in place

I have learned that "RCs don't dew up" is a myth.

I have 8 total hours of subs on NGC 2903 with a 6" RC. One night's worth - 3 hours of the 8 - I am pretty sure I had frost on the secondary mirror, because no set of flats produce what looks like a properly calibrated image. I have been playing around with various ways to take flats with this scope ...

That helps! Not the answer I hoped for, but the one I expected. I am collecting OSC duo-band data, so I must choose between using the new scope vs gathering more data.

"more data" won tonight, but I doubt I will hold out too much longer.

I suspect I already know the answer to this, as I am aware that StarTools does not work well with mixing different exposure times, for example. I have been imaging with a WO Z61 doublet, and have acquired an AT65EDQ (triplet objective with integrated flattener). The 65 has a slightly longer f/l (420...

Mine would be a Ha,Ha ;) And yes, this is a widefield view of the Cocoon, so a small fraction of the image is the Ha region, the rest is a rich star field. My understanding is that there is little-to-no Oii. I shot the L-extreme data under a full moon, so my thought was that including the G and B fr...