Lee_P

Lights are integrations of two-minute exposures. Flats taken using my ASIAIR PRO's auto flat exposure, which came out as 2.7s. Dark Flats 2.7s too, to match. Gain 100.

@Ouroboros @CloudMagnet I've made a few more noise tests: increasing the dithering, and trying Dark Flats. Nothing seems to make an appreciable difference in the end. So either I'm getting something wrong in the image acquisition / pre-processing stages, or my Bortle 8 skies are forever cursed to have this level of background noise. I've been staring at these images for hours though, so maybe some fresh eyes can spot something I'm missing! 🥴

I'm using an ASIAIR PRO, with the dither options being 1, 2, 3, 5, or 10 pixels. I've been using 3. Sounds like another test is called for, with a higher number. The variations being real is something I hadn't even considered 🤯

Ooh interesting, I didn't know there was a D3. Thanks for letting me know. I'll give it a go and will report back -- might be a while though, given all the cloud that's forecast! p.s. my P stands for "Pullen" 😁

Ah, I calibrated them with Flats and Darks, but not Dark Flats. Something else to read up about!

Having consistency in brightness was a good shout, it does make it easier to see the differences. I've tried to do the same with the original Iris Nebula data. Any thoughts on why the noise tests a few posts above show no real improvements after four hours? That's got me scratching my head.

I went down the eyedropper route. In for a penny, in for a pound! Whaddya make of that?

Yep, they were dithered. I'll have a crack at making the galaxies the same brightness.

I think you're right actually. I'm confused, surely it should get smoother with more data? Even the pattern of noise looks the same. Have I messed something up in pre-processing? 🤔 I'd be happy to do this, but you'll have to give me some tips on how! In the way I've been doing basic edits on these tests, the galaxy naturally gets brighter.

As CloudMagnet suggested, I've repeated the experiment with an extreme crop of M81. Looks like the same result to me: the first 10 hours are the most valuable. Data after that are still useful, but the impact certainly isn't as dramatic. I'll repeat with L-eXtreme data on a nebula once galaxy season has passed!

Good tip, thanks for sharing 😁

I think you're right, and it's funny you should say that because I've been editing the IKO Iris Nebula data trying to do exactly that 😁

Absolutely! That would make side-by-side comparisons rather difficult though. Not impossible I suppose, but too tricky for me 😅 FYI this is the final edited photo with all the data.

Super, well feel free to suggest what you'd like to see on a website dedicated to OSC from a city, Knowing that the effort will be useful to at least one person might motivate me to do it!

Thanks! The new-generation CMOS OSC cameras are very good. And work well with filters like the L-eXtreme. I'm increasingly coming to think that conventional wisdom like "don't use OSC from a city" and "you need a LPS filter" is outdated. To answer your question, for each image in this experiment I followed the same few steps in PixInsight. They were mostly to get a set of images that could be displayed side-by-side for fair comparison. * Crop * ColorCalibration * AutomaticBackgroundExtraction * EZ SoftStretch * SCNR (remove green) * Slight CurvesTransformation

Great! I'm tempted to make a website dedicated to OSC imaging from city skies. We're a particular niche. Could be a project for the Summer...

Thanks, I'm glad you found it interesting. No light pollution filter used. I haven't found them to be effective from my location. I posted another experiment, on this topic, here:

Wow, I've never worked with such good data! I decided to focus in on the central nebula and try to bring out its details. PixInsight: * LRGB combine * DBE * ColorCalibration * EZ SoftStretch * Create a mask, apply LocalHistogramEqualization to add contrast to the central nebula * Starnet++ to create starless version and starless mask * Save starless version as a TIF and export to Lightroom... Lightroom: * Topaz DeNoise AI * Boost Clarity * Boost Saturation and Vibrance * Save as TIF and export to PixInsight... PixInsight * PixelMath to add stars back in * Save as TIF and export to Lightroom... Lightroom * 1x1 crop * Boost Texture, Clarity, and a touch of Dehaze * Little bit of Sharpening * Colour Noise Reduction (I want the central nebula to be almost hypnotic, so this step was to desaturate the outer stars -- limiting the viewer's peripheral vision, focussing attention on the centre). * Reduce Highlights over the central star Just for fun, here's a comparison with the best data I've managed (Bortle 8, Askar FRA400, ASI 2000MC, no filters, 20 hours of integration). IKO wins 😂

Good shout, I'll download that and will have a play. Might make me a bit depressed about the quality of my data though 😅

I'd be interested to see a similar experiment to mine, using your 30 hours!

Well, I do happen to have 24 hours of data for M81 / M82, so perhaps I'll repeat the experiment for those! Once some nebulae are up in the sky again, I'd like to try using my L-eXtreme filter.

I thought it would be interesting to see the difference increasing integration times makes using my kit and sky conditions. So, I took 20 hours of data I'd collected on the Iris Nebula and produced images of different total integration times. Then I cropped in very close, and performed some simple edits in PixInsight, just to allow for comparisons. I thought I'd post the results here in case anyone could find them interesting or of use 😃 The earliest hours make the biggest difference, perhaps unsurprisingly! I'd say that the nebula's structure is there by 10 hours, and after that adding more time helps to smooth out the noise, but we're definitely into diminishing returns. It's hard to see much difference in the final few images, but there is a slight improvement. So, I'm thinking that 20 hours is a good target time for me to aim for. Info about image acquisition: * April 2021 * Bristol, UK (Bortle 8 ) * Telescope: Askar FRA400 f/5.6 Quintuplet APO Astrograph * Camera: ZWO ASI 2600MC-PRO * Mount: Orion Sirius EQ-G * Guide: William Optics 32mm; ZWO ASI 120MM Mini * Software: PixInsight, Photoshop, Lightroom * ASIAIR PRO, ZWO EAF

I think we're in the same boat. Maybe there's a filter out there that would help us with broadband targets, but for now I'm happy to just brute-force it with long integration times. I took the 20 hours of data from my tests, added in another four for good luck, and produced this image. It's not great, and a 400mm focal length scope isn't ideal for these targets, but at least we can get something even with our skies.

My tests seem to support this. I am assuming that it's LED lights swamping my skies though -- I don't know for sure that they're widely used in Bristol, but I wouldn't be surprised.

I recently saw FLO were selling a new light pollution filter: IDAS LPS-P3. I shoot OSC from Bortle 8, and figured this might help for broadband targets! (I use an L-eXtreme for narrowband, which works brilliantly). I already own an older-style IDAS D1, but don't routinely use it as I'm not sure of its effectiveness. Well, with these two filters in my possession, why not have a shootout and see the results? For this test I used an Askar FRA400 f/5.6 72mm Quintuplet APO Astrograph and ZWO ASI 2600MC-PRO USB 3.0 Cooled Colour Camera. All shots were from Bristol (UK) city centre. 120-second exposures. The target was M81 / M82. First up, I took a single sub using No Filter, D1, and P3. Each sub I edited slightly in the same way using PixInsight, just enough to make as fair a comparison as possible. Then I cropped very close into M82. Hard to make out much difference! The D1 produces a colour cast that takes a bit of work to even out in post-processing. The P3 retains natural colours well, and perhaps gives slightly better definition than no filter. More testing needed... so next I gathered three hours of data for each filter: Same again, to my eyes: all images very similar, but the D1 giving a slight colour cast. Time for round 3. When imaging I aim for long integration times, so let's try that here. I'd need to cut one filter out just because there are only so many clear skies. So bye-bye D1! Now it's No Filter versus P3. 10 hours of integration time for each. Who will emerge the victor? These are the stacks right out of PixInsight. The P3 has a bit of a colour cast, and a gradient -- to be expected actually, as the Moon was up more during the P3 test. Let's do some basic edits... They look essentially the same to me. Some very slight differences in the background, but explained by my use of Pixinsight's DBE tool to remove the Moon's gradient. Let's have a tight crop on M81: I really can't see any difference! These tests are leading me to conclude that the sources that make up Bristol's light pollution don't lend themselves to being suppressed by a filter. Maybe I've got lots of LED lights nearby. It feels almost heretical to say, but is there any point in light pollution filters from a city centre? Sure, from towns or areas with particular street lights (e.g. sodium), but from the middle of a big city? It seems to me that long integration times are the only way to claw back some of that signal to noise ratio. This Iris Nebula photo was taken with the same kit as the above tests, and is 20.5 hours of integration time -- no filters at all. I'm probably going to return the L3, and put the D1 up for sale. Unless anyone can see something I'm missing?!