symmetal

The documentation for GradientMergeMosaic just says to use the CloneStamp to remove offending 'pinched' stars on panel edges. 🧐

This tutorial also uses Clone Stamp but left to defaults apart from the radius. I tried it and this produced far worse results as almost none of the cloned pixels will be black at 0.5 softness, and they so you ended up with each 'fixed' star surrounded by a dark halo the size of the clonestamp. 😟

The Astro Imaging Channel had a talk by David Ault on GMM and at 45:30 he describes what he does about pinched stars. No mention of clone stamp.

In summery he draws a preview box around the offending star, notes the x and y extends of the box, and enters them into a PixelMath equation to replace every pixel inside the preview box with zero. Then repeats for every pinched star.

My 4x2 mosaic has at least 2 pinched stars on each edge, and 20 overlapping edges so I have to go through that palaver at least 40 times. 

There's a third party PI addon called DynamicPaintbrush which may do what I want, and let you paint in black with a hard edge, and there's a free 30 day trial so I'll try it out.

Else it's export all the panels as tiffs into PS, paint out the stars and reimport back into PI. This means it's 16 bit rather than 32 bit fp which may affect the merging though so I don't really want to do that.

Why's it so hard. 🤔

Alan

I've been building an 8 panel mosaic using MosaicByCoords to create the 8 panels, and DNALinearFit to intensity match the panels, which has worked very well. I then used GradientMergeMosaic to blend the panel edges together which also worked fine, apart from the known issue of bright edge stars causing 'pinched' stars as shown here. The mask shows the panel edges.

Here's the offending star on the top panel

I used CloneStamp to copy some black over the offending star as a recommended solution on the PixInsight forums.

However when re-running GradientMergeMosaic it fixed the star but a faint outline of the clone stamp is left. I think this is because the edge of the clone stamped area is still blending into the image background over a few pixels, and is not a hard edge, even though I've set the softness to 0.0. The preview circle still shows it blending at softness 0.0.

GradientMergeMosaic will only ignore true black areas so is treating the blended edge as image background and tries to merge it causing this effect.

is there a way to effectively clone stamp with a hard black edge, and not having it try to blend the cloned edge? Or is there some other method which is quick and easy to achieve this. As the PI forum recommends this method, there must be a way to do it.

Any PI experts able to help? 😊

Alan

The Zwo manual just states that the sensor protect window is AR coated only, and doesn't specify a different window for the colour version like some other cameras, so it passes IR and some extended blue. IR will be out of focus when you're focused on visible wavelengths so will lead to some image blurring. Depending on how well colour corrected the scope is, the shorter blue wavelengths may be out of focus to some degree as well causing noticeable blue halos around stars

The UV/IR cut will remove the out of focus IR and the shorter blue wavelengths leading into UV which should improve your image sharpness, and help with any blue halos. The Astromomik UV/IRfilters have three passband widths. L2 is the middle one and is likely similar to other manufactures UV/IR filters. The L3 has a narrower passband which cuts off more off the shorter blue wavelengths as well as the longer red wavelengths so reducing blue halos more.

Your posted image sharpness looks quite reasonable, but there's almost no colour present and it's faily black crushed so it's hard to say what UV/IR filter would suit you best. It's worth getting an UV/IR cut filter anyway if the camera itself doesn't have one, and the L2 should be fine, but whether you'd benefit more from the L3 I can't say from your image. The L1 is for very well colour corrected optics so wouldn't be the best choice for mid-price scopes.

Alan

Thanks @wimvb for your comments and for the link to the earlier article. I could try adding more data and see if it shows signs of an overdensity which appears to be the first indication for study. Compared to the other dwarfs studied I wonder what first drew them to Draco II as it doesn't indicate an overdensity. It's very similar to Ursa Major I in that respect.

The stars plotted are in the magnitude 18 to 21 range with star 25 (just visible on the image) being given mag 21.58

I forgot to say that Draco II distance is given as 70,124 light years, so it's just outside the Milky Way. I assume distances given are corrected as being from the Milky Way centre rather than from the observer.

I just thought the authors might like an picture for their wall really, rather than for further study, but the book you linked to looks interesting. 🙂

Alan

The first paper stated that the Sloan Digital Sky Survey (SDSS), Panoramic Survey Telescope and Rapid Response System 1 (Pan-STARRS1), and the Dark Energy Survey (DES) allowed for the discovery of faint Milky Way satellites. I thought I'd see what was available to download from these surveys and got these:

It was just outside the SDSS coverage area so no data.

Dark Energy Survey

The bright stars easily line up with those seen in the marked area in my image. 🙂

Alan

I haven't found any images of Draco II and just two published papers.

2016  Is Draco II one of the faintest dwarf galaxies?

2018  Pristine dwarf galaxy survey...of the very metal-poor Draco II satellite

Draco II is likely among the faintest, most compact, and closest satellite dwarf galaxies. Visually it certainly doesn't stand out, and its individual stars are indistinguishable from the Milky Way stars in the foreground.

The first paper lists 9 observed stars while the second paper lists 14 stars as belonging to Draco II in the appendix at the end. I made a custom catalogue to load into PI's annotation script, but there's a discrepancy as two of the observed stars don't seem to be in the 14 star list so I have 16 stars plotted with the 9 observed stars given the numbers assigned. The latter list includes numerous Milky Way stars as well as the 14 Draco II members so maybe two of the first list have been demoted to Milky Way stars.

The table columns g0 and i0 have values one of which could be apparent magnitudes.

The image is comprised of 3 hours of 2 min subs using a RASA 11 and ASI2600MC. Stacked in APP and processed in PI and PS, and no star removal processing was performed. I've included a crop of Draco II at the end.

Area containing Draco II.  But... I can't see it😟

 Here it is... 😁 Note all the stars seem to have the same colour.

Crop

I wonder if the authors of the reports would be interested in the image? Or perhaps send it in to the most underwhelming picture competition. 😊

Alan

1 hour ago, wimvb said:

Here's my first version, very different from yours. I don't process nebulae that often, so it's a bit trial and error.

Wow! Different to mine. 😲 You certainly have the blue stars reflecting off the dust. I think I relied on PMCC for the colour too much as it seems to have killed the blue again. I'll look over your process list for some tips. Thanks.

Alan 

A PC running 'Home' can be a Remote Desktop client but not a host. A 'Pro' PC can be either. So only the PC you want to control remotely must be a 'Pro' version.

Alan

1 hour ago, wimvb said:

I took the liberty of downloading and playing with your image. In histogram transformation I used the "auto zero shadows" button to get a different colour balance (not star colour, but background). This cleared up the colours, separating reds and blues more. I then increased colour saturation for red an blue to get this.

Thanks Wim to take the trouble. I didn't notice the Auto-zero shadows option. Certainly more varied colours.  I'll have to have a look. I've uploaded the original stack here if you, or anyone else, want to try it from scratch. 😀 It needs to be flipped horizontally for the right orientation.

VdB152.fits

Alan

Edit: I'll be uploading Draco II shortly which may interest you more. 🙂

1 hour ago, wimvb said:

Doesn't look overcooked to me. With so much nebulosity, it's very difficult to do proper gradient removal. The result will very much depend on where you put the samples. But this looks good to me.

Thanks Wim. I think I just used default ABE in the end. I wondered about the colour but I tried different different colour calibrations but went with PhotometricColorCalibration as it seemed to give good matching graphs, though I've found when using it on spiral galaxies it can leave them looking very yellow all over. 🤔

Alan 

Excellent capture. It's certainly in a hurry. 

Alan

Thanks @wimvb and @gorann 🙂 The PK.. designation of the 'galaxy with a hole' should have been a clue as it's from the 'Catalogue of Galactic Planetary Nebulae'.  Here it is at full size. The 'spiral arms' threw me off.

As you're both interested in less common objects, I wondered if you had seen my vdB 152 image I posted some time ago which had some interesting neighbouring structures.

Alan

This Astronomy Threads Explained  link may help. 🙂

Alan

42 minutes ago, wimvb said:

Shouldn't it? 😁

True. After all the effort of getting a fuzzy image of a black hole by the Event Horizon telescope, this is a much clearer one. 

Edit:  PK084+01.1 is already designated as a planetary nebula, so no fame for me. 😟

Alan

44 minutes ago, wimvb said:

Very nice image. 

I found this in Simbad. Nothing for the whole nebula, it seems.

https://simbad.cds.unistra.fr/simbad/sim-coo?Coord=20+45+37.80%2B44+15+02.8&CooFrame=ICRS&CooEqui=2000.0&CooEpoch=J2000&Radius.unit=arcmin&submit=Query+around&Radius=2

Maybe we should just call it the Pelican's chick.

By the shape and location it's more like the Pelican's Tick. 😁 Odd that it isn't designated, as smaller and fainter objects get a mention. 🙂

The little galaxy just above it PK084... seems to have an actual black hole in the centre. I'll see if this is a star removal artifact.

Edit: The hole is obvious in the Ha and just visible in OIII and SII so there's an actual bright ring at the centre of the galaxy. 

Alan

Dean,

I use Sharpcap's Polar Alignment routine on my portable mount and you can get it better than 1 arcmin very quickly with instant readouts on how far off you are. It uses the guide camera for measurements and there's no need for the guide camera to be well aligned with the main scope either. I looked at Polemaster's setup procedure and it does require quite a few time consuming steps to complete, so it's worth seeing if Sharpcap may be easier for you.

Alan

Forgot to add the annotated image. 🙂

Alan

First chance of trying out my Astronomik FastFR narrowband filters. This was obtained in a mix of Astro and Nautical Darkness and a partial Moon was in attendance. 100 mins per filter of 5 min exposures. ASI6200MM and RASA 11.

Processed in PI and PS. I based the modified SHO processing on a YouTube tutorial by Lefty's Astrophotography which was very useful. 🙂 I used StarXT on all three channels and just kept the Ha stars to add in later in PS as mono stars as the odd coloured stars and halos were a bit distracting. Halos left on the background after StarXT were treated in PS with the Patch Tool which I find is better than cloning. All channels also had BlurXT and NoiseXT applied before combining, and the Ha was also added back in as a Luminance layer.

I was very surprised at how well it turned out despite Deneb pushing its way in and causing a flare on the extreme top right on all three channels but also several large rings on OIII and to an extent on SII. The rings are hardly noticeable on the finished image, and I could have easily cloned out the top right flare.

I realised the framing could have been better, getting more of the Cygnus Wall, and have started retaking all the frames. Getting Deneb further out of frame also helps greatly with the rings which are barely visible on the new OIII. Even though the Moon was around there doesn't seem to have been any bad gradients on the channels.

I resampled the final result to 50% in PS. More than happy with the result, 😁 and thankfully it justified spending all that extra on the fast filters as I already had the standard 2" narrowband filters.

Cygnus Wall crop

There's also a small nebula patch top right of the pelican which I don't think has a separate designation. Shown here at full size.

Here's the OIII channel showing the large ring flares caused by Deneb off to the top right.

The stars along the top seem to show little spikes left and right, and I've since re-tweaked the Baader tilt adjuster which has improved them. OIII is very good at showing star defects. 🙂

I used Luminance flats for all channels and looking closely they don't quite fix the corners so I've since taken separate flats for the narrowband filters. Luckily fast scopes don't show dust bunnies from the filters.

Alan

Dean,

The longer exposures as such won't make the walking noise worse. Slight polar alignment errors is a main cause of this, not enough to give you elongated stars in one sub, but over an hour or so of imaging the image will drift over the sensor, and as you align on the stars during stacking, the camera fixed pattern noise ends up appearing as streaks on the stacked result. This isn't random in its appearance, (it's called correlated noise), so isn't removed effectively by stacking. Dithering in a random direction will break up this correlation making it more random, and so more effectively removed by stacking. 

It can take a while to settle after dithering, especially if you dither a large amount, though you have to dither by a enough pixels for it to make a difference, at least around 6 pixels or more at least by looking at your image. You don't have to dither every frame, (though the more often the better),  just as long as you dither around 10 times at least in your imaging run. If you aim to take 40 subs then dithering every 4 frames should be ok for the stacking to help remove the bad pixels. You also need to enable sigma reject in your stacking options to make this work effectively.

Alan

'Cosmic Geoff' and 'Carbon Brush' have pretty much covered what you need to know Chickpea.

Bench power supplies are used when developing new circuit designs or when fault finding circuit boards which have failed for some reason. In these cases having protection on what current the supply delivers can save further damage to the board by having more components or circuit tracks getting burnt.

For a tried and tested system like your mount these protections are not really necessary and a simple fuse in the positive wire from the supply should be fine. These fuses happily pass the surge current greater than their fuse rating for a fraction of a second, up to a limit of course.

Your power supply will have its own excess current protection independant of the OCP, to protect the supply itself, even if OCP or current limiting is not enabled.

I would just put an anti-surge fuse of say 5A in the mount power lead or a quick blow fuse of 10A and not have OCP or current limiting enabled. I tend to just use anti-surge fuses in situations like this. Current limiting can cause unpredictable behaviour when powering microprocessor systems even if it only limits for a few microseconds. 

Alan

On switch on, it will draw significantly more current for a fraction of a second, compared to its specifications while the electrolytic capacitors on your mount's circuit board charge up. This is perfectly normal and is what's causing the over current protection to trip if it's set too close to the specified current rating.

An electrolytic capacitor is effectively a short circuit when a DC voltage is applied to it. They are used as voltage reservoirs, connected across voltage rails to smooth the DC supply and help remove noise. They quickly charge up to the applied voltage and once charged their current draw is small.

OCP is effectively a quick acting fuse. If you want to use the OCP I would set the trip threshold to at least 8 or 10 amps. A common cartridge fuse type is called 'anti-surge' to prevent them blowing when a device is switched on because of this switch on current surge.

A standard brick type power supply rated at say 5 amps can deliver much more current for a short time without being damaged. It's output voltage may dip during this current surge but that's quite normal.

OCP and current limiting are different things. OCP is usually used to protect the power supply and is normally fixed just above its maximum current rating but should allow a short duration surge current above this value.

Current limiting just limits the current to a maximum value, but doesn't shut off the supply. It looks like you have the option of using the current limit value as the OCP trip threshold, but in this case it's not allowing any switch on surge current.

Alan

Hi Dean,

Your dark frame has dealt with the amp glow well, but your focus looks a little off as it's softer than your last 120s stack you posted. Maybe your guiding is contributing so 120s may be a better exposure to use. Your hot pixels seem to have turned into black pixels and 'walking noise' is quite evident by the black pixel diagonal streaks.

A bad pixel map created from your darks should replace the bad pixels with the average value of the surrounding good pixels which will help with the bad/black pixels. When creating the master dark there should be a stacking option to create a bad pixel map too.

Dithering is the best way to randomize the walking noise making it less noticeable, if you have an option to dither in your capture software.

Good luck! 🙂

Alan

It looks rather cheaply made but as Malcolm says, if it works then that's fine. The output cables look quite short so you may need extension cables which increases the number of connectors in series. Also check they are wired centre positive. It will still need to be covered when outside to avoid dew forming on the case. It's not earthed either, like higher power output switch mode supplies usually are, so you may get some tingling sensations when touching the mount. Not dangerous as such but can be unpleasant. 

The 30A supply you mentioned will need fitting in an enclosure with the mains terminals separately covered as well so entails a bit more work, but once done will be able to adapt to any setup you have fairly easily.

Alan

6 minutes ago, gonzostar said:

Thats a relief, Thankyou Alan for time and helping me out with these issues. Fingers crossed for plenty of subs. How did you neutralise in Photoshop? 

You're welcome. 🙂In Photoshop you can use 'levels' or 'curves'.

First display the 3 channel histogram so you can see what you're doing.

Using levels, select each colour channel in turn and move the 'Input levels' left most slider to the right until all three coloured histograms are on top of each other in the top histogram. Select 'colors' as the histogram's operating mode so you can see the individual colours. You'll probably leave the red channel alone and bring the green and blue channels down to match the red.

If the histograms are all bunched up to the left so you can't separate them initially, select channel RGB in levels and move the 'input levels' centre slider to the left (stretching the image) until the RGB histograms are away from the left edge.

Using curves, again select each channel in turn and move the left hand (black) input slider to the right to achieve the same results in the histograms as above. 

Don't move any of the sliders too far to the right, (which moves the histograms to the left) such that the left edge of the histogram starts getting clipped. Always leave a bit of space to the left of the histogram while processing. As a final move you can start clipping the left of the RGB histogram to give the most visually pleasing result.

Alan

Dean,

Good news.  🤗 Your latest postings look fine. I converted the fits to 16 bit tiffs to show in Photoshop as it's easier to visualize the results.

The 4 frame stack unstretched. The red signal is present now and not clipped. It's the lowest level of the three as expected and looks good overall.

The 4 frame stack with a quick stretch and background neutralized. All colours good and quite reasonable for just 4 frames. Amp glow present but easily fixed with darks. For uncooled the noise is reasonable too. Both the master flats look fine too. No clipping which is main thing. Some bad pixels but a bad pixel map and/or dithering will fix them.

For information, here's your single sub, which looked fine, stretched and enlarged greatly so that the single pixels are visible. The red pixels are the darker ones in each group of 4.

Everything looking good now. 🙂 Not sure what happened with your first posting where the red was black clipped. You may as well continue with the L-eNhance as the red output level is better than I would have thought given the relative widths of the bandpass segments and is quite useable.

You just need plenty of subs now on each target and you should have some good results. 😊

Alan