gorann

Thanks Andrew for allowing for the possibility of reddish dark nebulae😉

There are examples with more or less red. It just depends on the level of saturation chosen. If I just turn down the master saturation in PS it looks like this. Not sure if it is more "correct" rendention of the nebula.

Yes, in all astroimages bright areas show less noise than darker ones, but not all dark areas are reddish. So why do the darker areas in LDN1228 allways turn out reddish but not in Barnard 72 or 174?

Interesting Vlaiv. I just googled images for LDN1228 and a bunch came up and they are all red / brownish like mine, which was a releif🙂. Here are examples of LDN1228 from Astrobin: https://www.astrobin.com/363920/ https://www.astrobin.com/kwj3o9/ https://www.astrobin.com/okyb9k/B/ It is a very faint signal compared to the Iris with no really strong star shining on the dust. However, the nebulosity in the image is not uniformly red. The fainter nebulosity is more yellowish or even bluish on the left side of the image. If it was an artefact of processing faint signals then the faintest parts should be more red but it seems to be the opposite. Also, I have the impression that there was more red signal in the dark nebulosity after 6 hours than 2 hours. Could it not just be that there is some Ha emmision mixed in at various degrees? I could point out that LDN1228 was quite high up in the sky here so less atosphere than for many other objects. Images of other dark nebulosities are not allways red, some are quite grayish - black. For example, Barnard 174 is another dark nebula in Cepheus and it does not show this reddish colour: https://www.astrobin.com/71661/C/ https://www.astrobin.com/203604/ Here is an example of Barnard 72 that would have been imaged closer to the horizon and it is geryish black: https://www.astrobin.com/bijs57/B/

Thanks! I could have ovesaturated the red a bit in the 2 h version. The Ha is there but not as prominent after 6 h, now apparently mixed with other light picked up from those structures.

I have no experience with the other low f-value "Astrographs" around but they all are more expensive than the RASA 8, some rediculously expensive, and often with less aperture and most come with star spikes and a need to fiddle with collimation. Seems like the RASA 8 just keeps its factory collimation (even mine that was second hand), and maybe the non-Newtonian construction is less sensitive to collimation. My only issue with it so far is star shapes in the corners which suggest some tilt but they are usually easy to fix in processing, and the RASA 8 is only claimed by Celestron to work well up to a 22 mm image circle and I am pushing it to 28 mm (like in this image) with my APS-C chip, and still vignetting is minor. The RASA 11 at twice the price provides a larger image circle of 43mm but it weighs 20 kg instead of 8 kg and has a longer FL (620 mm compared to 400 mm) so much less field of view with the same camera. So, with a RASA 11 you need a full frame APS to get the same field of view that I have with the APS-C. I wonder what the impact on image quality would be, if any. Maybe a tiny increase in resolution on a very clear night, but then with a much more expensive camera and mount than with the RASA 8.

Thanks Vlaiv, that was about how I saw it. Maybe f/7 was not a realistic comparison. But there are many 400mm FL refractors at f/5 (or thereabouts) and they would need 37.5 hours.

Thanks, yes there are no shortcuts, although maybe f/2 helps a bit.

Thanks Andrew, much appreciated! Clouds have moved in and I look forward to getting a full nights sleep😵

This image is the result of having three times more data than in my previous post. Taken over three nights with the RASA8 and ASI2600MC (4 min exposures at gain 100). It made such a difference that I post it separately. So now 6 hours in stead of two hours and even at f/2, faint objects like these "dark" nebulae need integration time. Much less frustrating to process and no NR had to be applied this time. Data collected over three nights 24 - 27 August. Stacked in PI and processed in PS. No crop so the RASA 8 is quite good at filling up the ASP-C sized chip of the ASI2600. No flats or darks or any calibration done and not needed as far as I can tell. With regard to capturing photons, 6 hours at f/2 should equal 70 hours at f/7, if I got it right. Someone may correct me like @ollypenrice or @vlaiv...... For comparison I put the two hour version below the new 6 hour one. LDN 1228 is a dark nebulosity site in Cepheus. Quite some amazing shapes formed by the dark dust - food for fantasy. I am not totally unhappy for the clouds that have rolled in - have not got much sleep the last nights, not the least because the old Mac Powerbook decided now and then to stop downloading subs, so I had to keep a watch.

Not sure how the binning works on a colour CMOS with a Bayer matrix. Will it still give you RGB data? Or maybe you could make a Lum image from the binned data to use on the unbinned RGB, I am also not sure how bad it is with oversampling.

I got that exact scope - a 14" Meade ACF. It allready has a flat image so no need for a flattener and no need to worry about chip distance - just focus it (if it is in focus it is flat). If you go for a reducer you need to get one that is not both a reducer and flattener (a flatterer will distort a flat image), and then you need to get to the specified chip distance. As far as I know there are only two options for reducers that are also not flatteners: the Astro-Physics one mentioned here and the Optec Lepus reducer. I have the latter but I mostly use the scope at native FL with a full frame APS Sony A7s. I bought that camera specifically for this scope since it has big 8.3 µm pixels to avoid extreme oversampling. With the ASI2600 (3.76 µm pixels) you would do super-extreme oversampling at 0.22 " / pixel. Even with a reducer it would be extreme oversampling. I recently bought an ASI2600 myself to use for short FL scopes and I have not looked into the possibilities of binning for long FL scopes, but maybe it is possible. About attaching the camera it would just be to find anything fitting to the T2 thread of your camera.

So I could not stop myself from making a simple 50:50 mix and it looks quite good. Obviously one could be more selective and mix just the best parts/regions using layers.

Wim, you got a really nice colour and sky mix there, better than me. I like it a lot. I think I got a bit more detail out of the data so a 50:50 mix would maybe nail it.

Agree Olly, I just placed my order with Amazon!

The night looked promising by naked eye but going through the new subs of LDB1228 this morning only left 12 x 4 min min without obscuring high clouds. Will see what it contributes. Maybe a target for next lunar cycle.

Yes, that is exactly what I will do Maurice - just had a power-nap so I can stay up until it is done!

I can see that more data would not hurt so if the sky stays clear tonight I know what to do......

Thanks Alan! Yes the RASA is something quite different. You should get one for Christmas.

Thanks Tomato! Here it is supposed to be clear for one more night until clouds and the moon move in.

Looked a bit dark and glomy so here is a brighter version.

Thanks Mark!

This is an area in Cepheus from last night with the RASA 8 and ASI 2600MC (OSC). SQM showed 21.25 at midningt so it is not superdark up here yet and the nights are short. Only 45 x 3 min (gain 100), so just over two hours on a rather faint object that demanded quite a bit of stretching, so for the first time I needed a bit of NR for the ASI2600 data. Stacked in PI and peocessed in PS.

Thanks Olly! You are right, they colour may be a bit different but it also looks more like jelly than dust, and I have done no NR at all on this image (no need for that with this camera). Space jelly?

Yes, the best I have ever seen too! It does not look faint att all so maybe your image should come with a warning stating "Do not attempt this unless you can dedicate 47 hours to it".