Padraic M

4 hours ago, ollypenrice said:

I don't want to present myself as a pundit but my view is that, if you combine it at the linear stage, you have relinquished almost all control over it.

Let's remember that there is no 'natural' value for the Ha contribution. There is no way to calibrate it 'scientifically' with the rest of the image because the calibrated Ha is, surely,  just what is already contained in the red channel.* The whole point of the addition of Ha is to distort its contribution to the image and allow us to reveal structures otherwise not visible, though certainly present in scene we are photographing. This is an artificial process and we are the the artists - or artificers - responsible.

Olly

*This does not apply to those daytime DSLRs whose filters do block most of the Ha.

Absolutely Olly I agree, but you do still have some control over it, and processing at the linear stage is a relatively simple way to get started with HaRGB/LRGB/HaGB/(HaR)GB combinations etc. As you say, you are deciding how much you want to highlight the Ha content in your image at the expense of non-Ha red frequencies which is not a natural representation of the scene. You've given me food for thought on non-linear combination, work for another day!

@Rodd the Red stack contains all of the Ha light as well as other colours - the standard red filters on the market filter in a continuous range of wavelengths both shorter and longer than Ha at 656nm.

A narrowband Ha filter only allows through light at the Ha wavelength +/- half the bandwidth. It filters out all of the other red light that a standard red filter would have allowed through, but it doesn't include any light that is not transmitted by a standard red filter. So by selectively processing Ha and Red you are effectively emphasising that narrow band of Ha at 656nm by attenuating or even removing all of the other red wavelengths. All while (although not necessarily) leaving the green and blue colour levels untouched.

It might help your thought process to separate the original question into multiple questions:
1. how to register multiple channels from different cameras and scopes to a single reference frame and image scale
2. how to combine three OSC channels with one Ha channel to create a new three-channel RGB image which includes Ha to your desired recipe
3. as an advanced topic, and as detailed by @ollypenrice above, do you combine linear data only, or can you pre-stretch the channels to best advantage before combination?

For question 1:
I use Siril for stretching, but I don't use it for registration and integration. I use Astro Pixel Processor for that, and then import the linear integrated image into Siril. APP does all the hard bits relating to scaling and registering the images for you. It may be that Siril can do this too but I haven't tried it.

To build a HaRGB integrated image in APP, you need to first separate the OSC linear image into separate Red, Green and Blue channels. On the Calibrate tab, select 'Split channels'.

Then, integrate each channel separately to create Ha, R, G and B stacked images. You can register all lights to the same light frame at this stage if you like. Just make sure that the reference frame is integrated into its own channel, and then it is deselected but still marked as the reference frame so that it is not also integrated into each of the other stacks. (As an alternative, you can register and integrate them completely separately; then, reimport the integrated frames as Lights, register them together, save the registered frames and continue on as usual).

Note: When you are registering light frames from different cameras or scopes in APP you need to set some specific parameters on the Register tab, or the registering and integration won't work. The most important one is to deselect 'Same camera and optics'. It is also advised to select 'Use dynamic distortion correction'. If the two pixel scales and fields of view are reasonably similar this is probably enough. You can crop the channel images using the Batch Crop tool to remove any stacking artefacts. But if the scales and the FOV are very different, the techniques required become similar to creating a mosaic. There are good tutorials on the APP website if you need to get into this level of detail.
Also, having close to the same camera rotation angle on both setups is important, as even a small rotational difference can result in a lot of cropping around the edges.

For question 2:
There are many options for combining the four channels into a single image. In APP, after integrating each of the four channels, you can use the 'Combine RGB' tool on the Tools tab. You can play with different recipes or create custom ones here - try starting with HaRGB and playing with the sliders. Ha is usually added into the Red channel but you can experiment with how much of it you want to include, and also if you want to reduce the level of Red that comes from the OSC Red data. You can alternatively add the Ha data as a Lum channel; I find that adding it at much more than 20% washes out the OSC colour significantly. I do all of this is with linear data.

When you have saved the integrated linear HaRGB or LRGB image, you can close out of APP and continue processing (stretching) in Siril as you would do with any RGB image.

As the four channels are already registered, combining the channels can equally be done with Pixelmath in PI or Siril; or can be done with Photoshop or Gimp.

I don't think the RGB composition script in Siril will help - afaik that is for combining RG and B channels from a mono camera and filters into a single RGB image.

I'll leave question 3 to others with more experience!

That's a beautiful of piece of Victorian engineering art. I wouldn't like to have to tweak the polar alignment though!

A reprocessing of this image, using GraXpert gradient removal tool.

Workflow is Stack all subs in APP -> linear stack into GraXpert -> linear output into Siril for stretching/median filter/stretching -> final touches in Gimp. I think this allowed more stretching for the same noise levels, and brings out more detail.

3 hours ago, sinbad40 said:

I have a 533 and will be trying a multi panel of this at some point.  Was it 20% overlap used?

Yes, 20% overlap. The preview in the Framing tab looked fine.

I know that this is likely to be the start of a multi-year project, especially as for some reason the weather tends to be rubbish whenever Andromeda is in prime imaging position, this year being almost the typical example. But, as with all things that will take too long, the sooner you start the sooner it will be finished.

I have two set-ups for imaging:
- SW Esprit 80 & ASI1600MM Pro that I use for mono Hydrogen Alpha imaging in the city; this gives me 1.9"/pixel.
- SW 150PDS & ASI553MC Pro that I use for OSC RGB imaging under dark skies. Scale is 1.1"/pixel.

I had already captured some Ha as a 2x1 mosaic, giving all of Andromeda in frame. This weekend I had an unexpected clear and dark sky, with a little over an hour of Andromeda remaining before it set. An ideal time to start an RGB mosaic - NINA showed that I would need a 4x2 mosaic with the 533 to cover much the same sky as the 1600MM 2x1 Ha.

Given that the weather is as it is, I decided to go for broke and get a small amount of data on each panel - 2x5 minutes on each of 8 panels to be exact. The good news is that the skies stayed clear for the 80+ minutes needed for that pass; the bad news is that there seems to be a gremlin either in NINA's mosaic planning or the sequencer; I haven't figured out the full coordinate map just yet, but there's a gap in the data between the frames in row 1 column 3 and row two column 3 if you know what I mean. 

I can always come back later, or in later years, and fill that data gap while capturing more data for the full FOV. In the meantime, APP did a really good job registering all 8 panels, and adding in the Ha mosaic, but it struggled with the data gap in the middle. Multi-band Blending (MBB) at 20%, Local Normalisation Correction (LNC) off gave the best results. Also the colour rendering is off slightly between the top half and lower half (stacked separately).

So, a work in progress, but encouraging for continuing with the project. Now that I know the best settings for registration and integration, the next step is to stack all 8 panels in one go to see if I can get the colouration more even.

Data to date: 4x2 OSC RGB 80 mins (2x5mins each panel) + 2hrs 40m Ha 2x1 (1hr + 1:40)

This is 2hrs of OSC RGB on M78. As an emission nebula it's ideal for OSC in dark skies, and an ideal size for my SW 150PDS/ASI533MC Pro combo.

NINA capture, APP and Siril processing.

The green channel is really clean, but both blue and red were quite noisy. Is this a feature of high humidity in the atmosphere? I excluded an extra 1 hour of lights as 99% humidity gradually became 100% cloud. Quality improved a little with less-but-better data and I could stretch more without highlighting the noise.

Had a similar experience myself last night --- spent a few hours between midnight and ~2am alternating between Jupiter through the C8 and touring widefield with the binocs. Similar estimated SQM here - just under 22, but last night I think was particularly clear. I could see the equatorial bands quite clearly, whereas I normally have to make myself believe that I can see them.

I could see more of Andromeda's extremities than I normally see, and I definitely considered that I saw the Pleaides nebulosity.

In fact, one problem I had was, with so many stars to be seen, it was getting difficult to make out some of the constellations.

Woke up again around 5am, and Saturn was smiling in the window at me, but given that I'd only had a few hours' sleep at that stage, I decided not to get up. I'm setting up tonight for some AP, but while it's beautifully clear at the moment, the forecast isn't good for after midnight.

I'd agree with most of the posters here that an OAG is the best bet for both of the scopes you mention - both with mirrors, and especially the long f/l.

HOWEVER, I'm writing this with gritted teeth, as in my own personal experience (I'm sure everyone is different!) an OAG is the single piece of astro kit that I have most repeatedly wanted to fling against the wall as I found it to be an absolute pig/beast/dog to set up. I'm trying really hard to pick words to describe the experience that won't get me blocked from the forum!

I was using a C8 XLT which I finally gave up on as it's not really suitable for DSO AP, and the star shapes at the edge were horrible. Guiding was not great at all, but this is likely to be because of the poor optics out where the OAG was trying to operate.

On the plus side, once you do eventually get the back focus correct and the focus correct and the prism depth correct and the sensor angle alignment correct, you can lock everything up and leave it indefinitely. As @ollypenrice said though, you can do that with a guide scope too!

If I ever got to upgrade to an Edge HD I would bite the bullet and strap on an OAG.

The 533 is a newer model than the 183. Based on the specs alone, (https://astronomy-imaging-camera.com/product/asi533mm-pro/ and https://astronomy-imaging-camera.com/product/asi183mc-pro-color/) the 533 wins out on pretty much all aspects. Better QE, read noise, 14-bit ADC vs 12-bit, much bigger full-well capacity all make the 533 a more sensitive camera with a higher dynamic range. For the small price difference I think the 533 is a better bet.

I understand that the 183 suffered somewhat from amp glow, and the 533 does not. This is not a massive issue because calibration will remove this anyway and you will need to calibrate both cameras, but the less adjustment that is required, the better.

The other qualitative difference that could sway you is the size/shape of the sensor. The 183 has a rectangular sensor with more pixels. The 533 is square. Some folks don't like that but it's down to preference. Play around with Stellarium or telescopius.com to see the different image frames captured with each camera paired with your WO scope.

I have the 533MC and am very happy with it. If I have dark enough skies, I can sometimes get away without calibrating at all.

Yes, you can combine different image sets from different sessions on different rigs. Uncheck the 'same camera and optics' option and it will automatically rescale the images. There's also a 'distortion correction' option that addresses differences in curvature etc. between the two rigs. It's very smart.

Here's a test shot showing how the smaller FOV red, green and blue channels are registered in the centre (given that one of them was the reference frame), with the larger FOV Ha frame rotated and overlaid and added to the red channel. The size of the central RGB square is approx 3000x3000 pixels which is the sensor size of the 533MC so that suggests that all subs are resized to match the reference frame.

Thanks @Ouroboros. This was the first time doing this process and there is lots to learn. I'm surprised how much difference there is in the FOV given the pixel scale difference and the bigger sensor in the 1600MM. I'd like this to be a regular feature as I have the Esprit/1600MM setup in Dublin using narrowband to beat the light pollution, and the 150PDS/533MC is in Kerry under really dark skies, where OSC works well. I have both systems working reasonably well at this stage, so the thoughts of swapping the cameras from one to the other would fill me with dread! I'll need to do some more experimentation and see what works best.

I managed to capture some nice Ha data of the Crescent Nebula over two clear, if moon-lit, nights in the last two weeks. City skies, which Ha tolerates well.

I also had some RGB data from last year. The starfield was a bit psychedelic. iirc, it was also from two full-moon nights, but in otherwise very dark skies.

I've processed both sets together, using the two integrated stacks from APP, separated the RGB channels, and added Ha to the red channel as a new HaRGB image.

Stretching and tweaking in Siril, with final adjustments in Gimp.

The Ha data is SW Esprit 80/ASI1600MM Pro, and the RGB is SW 150PDS/ASI533MC Pro, so very different fields of view and completely different rotations. After a bit of trial and error, I managed to get APP to register the four channels perfectly, cropped and combined. Siril photometric colour correction and some judicious stretching. It's still got a lot of stars, but my experience with star reduction/removal hasn't been great so far. Might leave that for another day.

Siril registration really is great. I think the key to getting it to work was increasing the number of stars for Star Analysis to 1000, and using one of the RGB channels as reference for registration.

Capture times were:
Ha 37x 600s (6h10m)
RGB 70x 300s (5h50m)
Total of 12 hours.

Full Ha frame below just for reference.

15 hours ago, Bluesboystig said:

Thanks @Padraic M and @The60mmKid! 
If anyone knows what those circular artefacts are I’d love to know.. maybe something on the sensor/scope/filter? Or maybe while shooting flats there was something on the white t-shirt I used? Anything else? 

Play around with the calculators on this website: https://astronomy.tools/calculators/dust_reflection_calculator

Those spots are reasonably well defined, so not very far from the sensor. Definitely not something on the t-shirt. Based on your camera pixel size, and the focal length and aperture of your scope, the calculator quotes a distance of 2.7mm from the sensor. Does that sound like there's dust on the Optolong???

Anyway, rather than trying to clean your filter (you risk scratching it, and you will just get more dust on it anyway), getting proper flats will calibrate out any dust or dirt anywhere in the imaging train. Maybe just a quick blow from an air blower would also help.

Great shot, and well done! 

I don't use Deconv much, as if the image has any level of noise tends to will emphasise it. Something to come back to later when you have very smooth images.

Not much to add to the great advice above, just that when I started, it took quite some time to get my head around alignment. It's frustrating when you can't even get step 1 right, not to mind steps 2-100. The penny finally dropped when I realised that polar alignment and star alignment are two totally different things. Most of the manuals and guides assume that you know this already (how would we???). 

For polar alignment, you need to get the RA axis of the mount lined up with the celestial poles - also known as centered on a point very close to Polaris in the Northern hemisphere. Southern hemisphere is a little more complicated, apparently.

This can be done with no telescope on the mount. It could also be done in principle with no handset, or the mount powered off, but the mount and handset provide some tools to help. Key thing for me was that polar alignment is done using the altitude and azimuth adjustment knobs on the mount only, and not the handset direction arrows or the RA/Dec clutches. I also as a matter of course level the mount before PA, but as others have said, there are schools of thought on this. As a beginner, why not just level your mount. It's a little academic anyway because I doubt the bubble level on the HEQ5, or my eyes, are certified to sub-arcsecond accuracy.

As carastro said, on the HEQ5 you need to rotate the Dec axis by 90 degrees to use the polar scope, so by definition you can't polar align in home position.

Once this is done, you can mount your scope, go to home position, and do a star alignment using the handset and the arrow keys.

I suspect that nothing turns beginners off astronomy faster than an equatorial mount!

On 31/01/2023 at 18:51, iapa said:

here is what I presented for CFO to gain approval for my build.

Microsoft 365 (Office).pdf 230.37 kB · 99 downloads

I can't believe you wrote a PID for the observatory build! I'm managing a banking system upgrade and can't get them to write a PID 😞 .

But I'd like to see your governance structure including the process for managing change requests. Also, you haven't recorded the CFO's approval so this isn't auditable as it stands. 

Don't mention it, glad to be of help 🙂

p.s. I'm jealous. Lovely location and great build.

Hi there @Gibbous Mars and welcome to the money pit club!

I have the 150PDS and it's a fine telescope, and I'm sure the 200PDS is in the same league. I also have an 80mm high-end refractor and can comment favourably on both and also the pros and cons of both.

Reflectors give excellent value for money in terms of aperture. You may already have checked out the astro calculators (e.g. astronomy.tools) to see the difference in resolving power and light grasp of a 150mm vs an 80mm, and it's significant. Reflectors however can also be more work to get working correctly than a 3" or 4" refractor. They're bigger and (usually) heavier, need regular collimation, and generally with longer focal lengths which makes operation that bit more difficult.

I'm sure you know that the PDS range are designed to be suitable for astrophotography (Parabolic mirror/Dual-speed focuser/Short tube) so they are a good starting position even if you don't intend to start astrophotography immediately. However you'll also know if you read around these forum pages that there's a big difference between observing and AP. 

The usual rule of thumb for AP is to halve the stated payload of your mount - so in that case, the ideal max weight of scope (plus all peripherals) on an EQ5 would be ~5kgs. HEQ5 Pro on the other hand is rated for 11kg imaging, 18kg visual. That means that where the EQ5 is pushed beyond its limits with the 150PDS, the HEQ5 gives some headroom. If you haven't already bought the EQ5, I would strongly recommend you spend the extra ~€300 and get a HEQ5. You wouldn't need to go as far as an EQ-6, although I managed to pick up a NE6-Pro second-hand on these forums, which is an excellent mount, for less than the price of a new EQ5. 

With either of these mounts, I would push for the 150 rather than the 200. These reflectors are big beasts, surprisingly heavy especially when fully loaded with AP kit, and because they are so big they respond like heavier scopes when on the mount. This is partly because they can catch a breeze very easily, but also because of their length, they act like levers.

For observing, you should consider buying some decent quality eye pieces. The 2" EP that comes with the 150PDS is not great quality. I had previously bought the Skywatcher box-set of 1.25" EPs which don't have a super reputation, but even these are better than the stock 2" EP. For the same price, you could probably get 2 or 3 good-quality EPs that will transform your viewing experience. Manual focusing will be fine, but get a Bahtinov mask to help get the sharpest focus.

For AP, I have the ZWO ASI1600MM Pro, an old workhorse camera that has been somewhat superceded by some of the newer, zero-read-noise cameras but still does a really good job. Because it's a mono camera, you would need filters and a filter wheel to construct a colour image either from a set of (L)RGB filters or from one or more narrow-band filters (Ha, SII, OIII). I'm in Bortle 8 Dublin city centre skies so I stick mostly with Ha because of the light pollution. I also have a ZWO ASI533MC Pro one-shot colour camera that I use when I'm in dark skies, and I really love how much easier it is to get good full-colour results from it. This is possibly due as much to the dark skies as it is to the camera. Few people use OSC cameras under city skies, but it can be done. If your budget can stretch to it, the newer ASI2600MC Pro really seems to have blown these other cameras out of the water but it is pricey. There's a Rising Cam cheaper version using the same sensor that is very much worth looking at. Of course you can also go down the DSLR route and even get an astro-modified DSLR but while usable they are not ideal for long-exposure DSO photography, and are harder to calibrate than dedicated cooled AP cameras.

Bear in mind that for AP you really will want to look at electronic focusing, guiding with a separate guide scope and guide camera, and a connection to a computer of some sort so that software like NINA or APT can control your imaging sequences. Of course, there are two types of AP - Planetary and DSO - and they require different scopes, cameras, techniques and software. I'm only dealing with DSO here as it's what I do, but also as you're leaning towards a Newtonian reflector you are also probably looking primarily at DSO.

The PDS scopes also leak light both from the rear (primary mirror) end and through the focuser tube. This is probably OK for observing although there will be some loss of contrast, but for AP it does cause light streaks on the images and really needs to be sorted out. Tinfoil and a swimming cap will do the job. There are also a few other mods that are highly recommended such as loosening or replacing the primary mirror clamps because they cause triangular-shaped stars. It sounds scarey but is not too bad as long as you're careful with the mirror and have some patience 🙂. You will also need a collimator whether you're doing AP or visual.

AP quickly gets very specialised and can cost a whole lot of money. Lots of people, myself included, start out by saying they want to do some observing and a little bit of AP, but if the AP bug bites, they end up head-over-heels down the rabbit hole of equipment and software. Things that sound irrelevant like image noise, poor star shapes, less-than-100% focus, poor tracking, internal reflections/star halos etc. are really frustrating once you see them in your pictures, and it's a never-ending process to eliminate them to an acceptable level. That's why many will recommend a good quality 4" reflector on a EQ-5 or better mount as a starting point for AP as an easier way to cut your teeth. A 150PDS on a HEQ5 is equally good, but is a little more difficult to fine-tune and manage.

hth and doesn't add more confusion!

That's an excellent start! There's some good detail in there, in both galaxies, you've got spiral structure in M81 and the starburst in the Cigar.

Most points already covered above. The diagonal stripes are 'walking noise' and will be removed if you dither while capturing. NINA supports it with very little effort - in the Smart Exposure control you can just say how often to dither. It takes a little time, so keep it to every 3-6 frames.

You're using Dark frames, but you don't mention Flats. Well worth figuring them out, even though they're a bit of a nuisance, but they will likely sort out those faint dark smudges, which are probably dust motes on the sensor or on the lenses, close to the sensor.

Other than that, get more data! 40 mins is not a lot, especially in Bortle 7/8.

No, fraid not. Enjoy! Hope you get some clear skies.

I attached a second dovetail to the top of the tube rings. I don't have it to hand at the moment so can't show a photograph, but it did entail buying new mounting bolts for the dovetail plate.

You could continue to use the finder scope fitting. However there are two advantages that I get from using the dovetail ring - it's much easier to balance the whole assembly on the mount, and the second dovetail provides a handy carry-handle. The scope, complete with camera and guidescope, is surprisingly heavy!

Not sure this is a power issue - that message usually displays on SW mounts when the serial comms pins on the microcontrollers have been fried, thanks to having been fed 12V rather than 5V. Could be 'a wiring issue with the handset' as you say. I have unfortunately managed to do that when trying to wire up a diy ftdi cable.

Have you tried @malc-c as he's pretty good at diagnosing these issues?

On 04/03/2023 at 06:28, Nicola Fletcher said:

the Irish Astronomy Week is coming up this month and has loads of events -  see https://www.irishastronomyweek.ie. I’m also a member of the Irish Astronomical Society. There are several clubs around the country and the midlands astronomy club is having their COSMOS star party on 25th March which I’ll be going to - see https://midlandsastronomy.ie/cosmos-2023.

Thanks @Nicola Fletcher for bringing COSMOS up! I hadn't come across this before. Will take a look at the diary, and the forecast! 

No wonder it's been cloudy since Christmas!

Welcome onboard and good luck with your new scope.

Wow how did that happen? Looks like a clean cut, but it sounds like it sparked.

The Pegasus PPBAdv is fantastic, you'll never look back. What PSU will you use with it? That should be the only mains near the mount (excluding laptop if you're using one). I use the Nevada Radio 30A PSU powering the PPBAdv and low voltage to everything else from there. The PSU should go in a weather-proof box of some sort.

Some people run low-voltage with a long cable from inside the house to the mount, but that can have other issues like voltage loss in the cable. That can be countered by having slightly higher voltage at source (Nevada is 13.8V) or using a buck/boost converter at the mount to counteract any cable loss and reconstruct the 12V.