Sunday, 5 February 2017

Bright Spot and a Filament 4th September

The conditions were far from great, but in the depths of winter it is nice just to get an image of the sun as it skirts the roof lines and tree tops of the urban environment.  Now into the start of february the sun climbs ever higher in our sky, and while it still dances with the urban obstructions it is visible for longer and longer each passing week.  There was a small surge on the limb, and with a wispy filament it made for a frame with the Skywatcher ED80, Double stacked Daystar Quark and a PGR Chameleon 3 camera using 2x2 binning to try and tame the unsteady atmosphere.

AR12632 in Ha 4th February

This little decaying active region had very little other than a few plasma rifts going on, and, with a sun heading towards solar minimum is why a scope like the 0.2m Airylab HaT is the way forward.  This 'wide field' shot was taken with a skywatcher ED80 and a double stacked Quark.

Chromosphere on The Limb In Calcium Light 4th February

Not really a lot going on on in this image taken in Calcium light of the north eastern limb of our star taken with the 80mm scope at 2000mm focal length with the PGR CH3 and 2x2 binning.  What is does show is the 'hairy' limb of the sun, or the chromosphere in profile, sometimes called the spicule layer in Ha images.  With a quieter sun now upon us this is something I want to focus on for animations with a high temporal cadence in the months ahead in this years solar season.

Saturday, 4 February 2017

AR12629 in CaK 4th February

While todays seeing wasn't great there were moments when it showed some promise, to the point I decided to get out the 100mm Tal100R refractor.  Stopping this down to 80mm with a Beloptik tri-band ERF and running at 2000mm focal length I was able to get some close up views of this departing active region revealing some quite small scale detail. Taken with the homebrew CaK filter and the PGR Chameleon 3 camera using 2x2 binning.

CaK Full Disk 4th February

Apart from the decaying active regions that were heading towards the suns limb there isn't a lot happening on our sun in Calcium light at the moment.  This image was taken with the 40mm scope at 400mm focal length with the PGR Chameleon 3 camera.

Eastern Prominence 4th February

This subtle little prom on the suns eastern limb had lots of faint detail tucked away that I didn't realise until I processed the image.  Taken with the Skywatcher ED80, Double stacked Daystar Quark and the PGR Chameleon 3 with 2x2 binning to try and tame the the poor seeing.

Small Prominence 4th February

This small prominence was hanging on the boundary of filaprom / prominence on the western limb, but I like the way the subtle detail came out.  Taken with the ED80, double stacked quark and the PGR Chameleon 3 with 2x2 binning.

AR12629 in Ha 4th February

Seems the turn of february is a tipping point for me with the sun just about above most of the tree tops for most of the morning, following 3 months of grabbing quick views of suns between the branches.  With blue skies prevailing I decided to give the Daystar Quark its first run of the year on the back of the Skywatcher ED80.  Seeing was awful so decided to use 2x2 binning on the PGR (FLIR) Chameleon 3 camera to give effective 6.9um pixel size, which, together with increased sensitivity and shorter exposure time just about did the job.  Bear in mind the sun was still below 20 degrees altitude in the sky.  The sun is pretty quiet at the moment with this relict active region heading towards the limb really the main feature of note.  I needed to use flats with this image as there were dust bunnies galore - I need to clean all my glassware before settling into the 2017 solar season proper.

Ha Full Disk 4th February - The Sun Finally Comes Out!

Finally after over a month of no real clear skies, or, no clear skies when I can actually observe it was nice to have a saturday morning where the sun was out.  Certainly not totally clear skies, there was a lot of high cloud but it was thin enough to image.  It's also pleasing to see how much higher the sun is getting in the sky now, the 2017 solar season is starting!  This image was taken with the double stacked PST at 400mm focal length with the PGR Chameleon 3 camera.  Disk detail is low at the moment but there were a couple of small delicate prominences on display.  Just a bit to early in the season to be zooming in with bigger scopes effectively.

Monday, 2 January 2017

A Busy Western Limb in Ha - 2nd January 2017

Hydrogen Alpha at 656.28nm was proving itself to be the wavelength of choice on this, my first imaging session of 2017.  There were plenty of smaller scale features to be seen including a number of small but well defined prominences, some of which merged into filaproms.  A small emerging flux region crackled with magnetic energy, however is unlikely to develop into much more, and on the disk a number of darker filaments, cooler clouds of solar plasma held aloft by magnetic fields could be well seen.  The image was taken with a Coronado PST double stacked with a Lunt50 etalon along with a PGR Chameleon 3 camera and a Daystar Interference Eliminator to apply tilt to the optical plane to get rid of banding issues caused by Newtons Rings.  

Eastern Filaments - 2nd January

The eastern limb of the sun was the quietest today, with a very small area of inactive plage, however the limb offered a nice collection of small prominences, filaproms and filaments.  Taken with a double stacked PST, PGR Chameleon 3 and a old and dirty 2x barlow that has graced the image with dust bunnies.

Ha Full Disk - 2nd January 2017 - Happy New Year!!!

As I use this PST more and more i'm slowly starting to get a handle on how it works, and how the orientation of the double stacked Lunt 50mm etalon that i'm using on it manifests itself in the final image.  Today was one of those days that was quiet in CaK wavelengths, but in Ha there was a whole host of interesting smaller scale features that could be seen.  The proms and filaments were the star of the show, but there was a small and interesting emerging flux region passing towards the western limb.  The bright plage towards the eastern limb doesn't seem to be doing much at all.  Taken with the Double stacked PST and PGR Chameleon 3 camera.

Easter Plage in CaK Light - 2nd January

When I saw this area of plage coming around the limb a few days ago I was optimistic there might be a few spots tucked away in there - alas no!  Any activity is very small scale or deeply buried within our star.  Taken with the 40mm scope, 2x barlow, homebrew CaK filter and the PGR Chameleon 3 camera.

Western Plage In CaK Light - 2nd January

A closer look at the small area of plage heading towards the western limb in Calcium light reveals a smittering of brighter white spots indicating possibly developing activity, maybe and emerging flux region?  Taken with the 40mm scope and a dirty 2x barlow nosepiece which has given a shadow of dust bunnies on the image despite a good clean - a new barlow is in order for a new year I think!  Taken with the PGR Chameleon 3 camera and Daystar Interference Eliminator.

CaK Full Disk - 2nd January

The sun was quite blank in Calcium light today, a couple of brighter areas of plage towards either limb, possibly the one on the left will become an emerging flux region as seemed to be crackling away with a few brighter spots.  The faintest hint of the proms visible too.  Taken with the 40mm scope at 400mm focal length with the homebrew CaK filter and the PGR Chameleon 3 camera.

Thursday, 29 December 2016

When Less Is More in Solar Imaging - Ha Full Disk 29th December

I've been messing around with a PST for some time now since the summer, first double stacking it with a Lunt 50 etalon, the BF5 has been replaced with my BF10, as IMHO, this particular filter offers better contrast.  I've also shortened the eyepiece holder on the PST, so that all the usual issues of cameras not coming to focus without a barlow etc are a thing of the past.  Today, in my new found hour long winter season viewing window I tried a different experiment, which barlow offered the best view.  I had 2 to choose from, my astro engineering magnimate and a bog standard Skywatcher 2x barlow.  The PGR Chameleon 3 with its 2048x1536 pixel sensor offers plenty of real estate for such an exercise. After taking numerous images the results kinda didn't surprise me, the best image was the one without a barlow at prime focus, it was noticeably sharper, with more contrast and more fine detail.  It gives a 1200 pixel wide disk, which, for displaying via the web is ample.  I still need to get the perfect tilt with the Daystar Interference Eliminator, I feel some index marks coming on. Next steps may have to be to lose the PST Black Box (and it's potentially astigmatic) penta prism assembly and have a focuser directly on the back of the etalon.  With the correct spacings it should work well!

AR12261 in CaK - 29th December

With my new found gap in the trees i've now over an hour to pass solar imaging in the winter season around solar noon, and, after messing around with some full disks still had some time to spare.  Seeing wasn't good with the low sun as you would expect, but I decided to crack out the Skywatcher ED80, and stopping it down to 60mm I took a closer look at some of the plage that is currently visible in Calcium wavelengths.  Viewing the image full size there is the smallest of pores visible in this relic active region.  Taken with the homebrew CaK filter and the PGR Chameleon 3 camera in conjunction with the Daystar Interference Eliminator to tame Newtons rings that can be a problem.

CaK Full Disk - 29th December

Another clear and frosty day here in Brierley Hills, and with my new found 'gap between the trees' available for a full hour around midday it would be foolish of me not to try and exploit it for a bit of solar.  Our sun is very quiet at the moment, with only a few areas of white plage visible on the disk, indicative of slightly higher magnetic fields, alas no strong enough to form any sunspots.  The air was very clear, and, it is possible by clicking on the image to view it full size to see the spicule ring around the limb, along with ghostly pale views of todays prominences.  Also, at 9 o'clock on the limb a small surge is visible.  Taken with the 40mm scope at around 500mm focal length with the PGR Chameleon 3 camera.

Tuesday, 27 December 2016

North West Quadrant - 26th December

A pretty blank quarter of sun all bar a few filaments and small areas of plage.  There are a few smudges which are the result of a couple of chips on the glasswork of my el-cheapo 2x barlow which was used for this pic 😶 - time for a new year barlow lens me thinks!  Despite this i'm pleased with the way this image came out given the low altitude of the sun and the poor seeing that this presents.  The focus feature in the Genika capture software really helps with this.  The image was taken with a PST double stacked with a Lunt 50 etalon and a PGR Chameleon 3 camera, along with the very effective Daystar Interference Eliminator to tame the issue of Newtons Rings easily with minimal tilt to affect focus across the frame. 

Monday, 26 December 2016

Small Prominence, Small Filaprom - 26th December

It's days like today when a double stacked scope is really needed to see the smaller and finer details on our star.  Double stacking reduces continuum leakage from the wings of the Ha line at 656.28nm, and the consequence of this is increased contrast, making delicate filaments and filaproms easier to see, in a single stacked scope these tangible details are just washed out.  While very little was visible on todays sun, the double stacked PST did a good job of showing these more subtle features.  My favourite in this shot is the small filament and the hazy filaprom.  Also working very well was the Daystar Interference Eliminator in doing a great job of applying just the right amount of tilt to get rid of the annoying Newtons rings!

Closing In On Not Much... 26th December

My new found 'gap in the trees' around midday in the winter season has given me a bit more time to image.  I tried zooming in a bit with the 40mm scope as realistically this is all the seeing would allow with such a low sun, alas, there was not much to see at all!  It really did need a much bigger scope to zoom in on some of the plage regions to close in on the smaller scale detail.  Either way, nice to be able to image this late in the year!

Boxing Day Sunshine In Calcium Light - 26th December

Boxing day dawned bright and clear, and despite the low sun I was determined to make the most of the day.  The sun is devoid of spots at the moment, but, looking in Calcium light at 393nm it was possible to see several small areas of brighter, white plage - these magnetically frothy regions hint at very low levels of activity, maybe, deeper within out star.  I was testing out some new technology today too:  Firstly the focus assistant in the Genika capture software allowed an empirical measure that the focus was as sharp as the conditions allowed, which, with a north westerly air stream and a low sun wasn't as good as I know is possible with this setup.  Secondly the Daystar Interference Eliminator allowed me to easily apply the minimal tilt needed to get rid of Newtons Rings yet retain a sharp focus, this is a piece of equipment that I feel is going to be invaluable in imaging with other setups in the future.  This full disk was taken with the 40mm scope at ~500mm focal length with the homebrew CaK filter and the PGR Chameleon 3 camera.

Boxing Day Ha Full Disk - 26th December

The weather turned from the storms of Christmas day to building high pressure and clear skies on Boxing Day.  I was keen to try out my Daystar Interference Eliminator as a means for getting rid of Newtons Rings that afflict my imaging with the PST and PGR Chameleon 3 camera.  I'm pleased to report this is a very effective solution that allows the user to very quickly and easily adjust to a minimum tilt (required) position to give minimal affect on focal shift across the image frame.  I'm looking forward to being able to do more testing with this great little device as the sun climbs higher and higher in the sky now we are past the winter solstice.  Wish there was a bit more to see on the sun though!  Merry Christmas to all! 😃

Thursday, 22 December 2016

Near Solstice Sun - 22nd December

I would have liked to get an image on the 21st December to mark the winter solstice, alas, UK weather was not in my favour, so, i'll have to settle for the day after!  At an altitude of less than 10 degrees in the sky when this image was taken it was a race to get the sun in between the branches as it passed amongst the trees on the urban skyline.  With so many branches passing in and out of the field of view it can be a challenge to actually get a decent focus on our star.  The sun is remarkably quiet at the moment with only a few brighter areas of inactive plage, there are several smaller areas of filaments, and also some smaller prominences on the limb.  Taken with a PST double stacked with a Lunt 50 etalon, running at just over 500mm focal length with a PGR Chameleon 3 camera.  I'm pleased to get an image of the sun at this time of year, at least now with each passing day it is getting that bit higher in the sky!

Sunday, 4 December 2016

CaK Full Disk - 4th Decmeber

The sun was low in the sky this afternoon, and was a waiting game for it to pass between the gaps in the trees so that I could image it.  AR12516 is a nice active region, that while not strongly active is active none the less.  It would have been nice to be able to get a close up of this area, but, the seeing was not playing.  This shot was taken with the 40mm scope at ~500mm focal length with the homebrew CaK filter and the PGR Chameleon 3 USB3 camera.

Ha Full Disk - 4th December

The sun really is low now as we're only just over 2 weeks away from the winter solstice, where, for observers in the northern hemisphere the sun is at it's lowest in the sky.  From that point onward the sun climbs higher and higher in the sky with each passing day.  I'm severely limited at this time of year with the low sun and it being blocked by the urban skyline of trees and rooftops, but luckily was able to find a gap to observe just after midday.  Considering we are heading towards solar minimum there was plenty of nice activity including nice prominences and filaments, but also in the form of largish AE12615 which has been crackling away with minor B and C class flare activity since it rounded the limb a week or so ago.  This image was taken with the PST double stacked with a Lunt 50 etalon, and with a barlow to take the focal length to ~500mm it nicely filled the frame of the PGR Chameleon 3 camera that was used.  This is a stack of the best 100 images from a 1000 frame avi.  

Saturday, 19 November 2016

Ha Full Disk 19th November

It was difficult to get tuning spot on with cold fingers on this frosty november morning and the left of the image is slightly off, but despite the sun being quiet there were quite a few nice features to see with the double stacked PST running at 500mm focal length with the PGR Chameleon 3 camera.

CaK Full Disk 19th November

The sun was very low this morning at just after 9am, and with a heavy frost evaporating from the roof tops, trees and fences the air was filling with a rising mist which I was observing our star through.  As a result exposure time needed to be lifted.  A little too much tilt the left side of the image is out of focus somewhat.  Taken with the 40mm scope at 500mm focal length with the homebrew CaK filter and the PGR Chameleon 3 camera.

Sunday, 6 November 2016

A Review Of The Solutions To Newtons Rings In Solar Imaging

Newtons Rings are a problem that have afflicted solar imagers, in a variety a wavelengths, for some time, resulting in a series of alternating light and darker bands or concentric rings that appear super imposed over the target image.  Noticeably fickle in their apparition they can appear for some people in a particular optical / camera configuration, then not be visible for other using exactly the same setup.  Imagers have come up with a number of methods to remove or reduce them:  

One method involves letting the image drift or 'drizzling' the image across the field of view when taking the capture file, and then relying on the stacking software averaging these out in the stacking process.  Whilst it can be an effective way, it is not always convenient, feasible or desirable to do this, and the results can be variable depending on the orientation of the banding.

An alternative is to use a flat field; where the imager places an opaque material e.g. cling film or a clear plastic bag over the objective of the telescope and takes an image (or series of images).  This 'flat field' is then applied and subtracted from the final image during the stacking process automatically by the stacking software.  This has the benefit of it also removes the effect of 'dust bunnies' the dark shadow spots created by dust / detritus on the camera sensor.  Whilst this would appear to be all that is needed to remove the effect of Newtons Rings, sadly it is not.  The technique cannot be applied to full disk images, like the one above, it is only suited for close ups.  It is not wholly suited for making animations either as the effects of Newtons Rings also vary with the temperature of the camera being used, and if the camera is warming up, the effect of Newtons Rings will vary with time until he camera reaches thermal equilibrium.  

 Another method is to use a tilt adaptor as shown to the left.  This consists of 2 plates with 3 sets of adjusting screws allowing the user to offset the tilt between the 2 plates relative to each other.  This works by then effectively tilting the path of the light path relative to the chip / face plate on the camera where the newtons are occurring.  This tilting alters (makes longer) the effective path length of the light in the offending chip / face plate and as a result the constructive - destructive interference of the light no longer occurs and the problem is resolved.  With this method a solar imager needs to make a light shroud to go over the gap between the 2 plates, as, in the daytime this leaks light and will reduce the contrast in the solar image.  This is easy to do with something simple such as electrical tape.  In addition this type of adaptor adds about 10mm to the optical path which, if a Barlow lens is being used will result in a slightly higher magnification (than without), which may or may not be an issue for the user.  This type of adaptor works well if you do not need to adjust the tilt, but for different wavelength / camera / optical configurations changing the tilt can be fiddly and not really an effective way of doing it.  In addition this type of adaptor is available in a range of connectivity options including T2, M48 and SCT threads for at the time of writing ~£50 from a variety of international retailers.
 A variation of this is the one offered by Rowan Astronomy , shown to the left, which offers a spherical joint between the flanges to stop light entering the device, this is at the expense of additional back focus, which, may or may not be an issue.

Another alternative is the Daystar Interference Eliminator shown to the right and currently retailing for £/$149.  Whilst initially this may seem to be an expensive alternative to the adaptor above it offers several benefits.  Firstly the 2 curved surfaces remain closed at all times and as such there is no light leak to reduce contrast of solar images.  Secondly the 2 large thumbscrews allow easy 'real time' adjustments for different camera / wavelength / optical configurations.  The third aspect which most people over look the significance of is the fact that this works by tilting the camera off normal while keeping the centre of the image sensor stationary, so that focus, framing and vignetting are not changed with tilt.  The tilt changes the angle of incidence and optical path lengths inside the optical sensor, mitigating the interference.  As with the adaptor above this solution adds about 15mm of additional back focus, and if used with a Barlow lens will result in a slightly higher magnification, which, again, may or may not be an issue for the user.  The Daystar Interference Eliminator is the technically best available solution for Newtons Rings, but is also the most expensive, but this is reflected in the quality and effectiveness of the engineering employed.  It is available in T-mount and C-mount variations.

A final alternative is the use of a 'wedge prism' or 'Risley' prism.  This is an optical piece of glass where the 2 opposite faces are set at an angle rather than being parallel.  This has the effect of deviating the beam of light away from the normal axis, so that when it passes through the optical sensor it has a slightly different path length and so the interference effects of Newtons Rings are negated.  The wedged face of the prism is the one that needs to face towards the sensor.  The prisms are available in a range of wedge angles, usually 2, 4, 6 degree beam deviation angles, with the former 2 being suitable for solar imaging.  They are available with broad band optical coating from Thorlabs for the very cost effective price here in the UK for £24.  Being 25mm in diameter they are easily adapted to fit in the C-mount nosepiece of a camera, with a variety of retaining rings etc available from Thorlabs to secure these in place.  Unlike the 2 tilt adaptors above these add no additional back focus to a setup, with no change in the resultant magnification of Barlow lenses that may be used, which, again, may or may not be of concern to the user.  On the down side for this solution the tilt of the system is fixed, unlike the variable option of the 2 options above.  Also, unlike the Daystar solution, the tilt is not from the centre of the optical sensor, so, as with the first tilting adaptor, there can be focus issues at the edge of the frame or subtle vignetting.  The image at the top of this post was taken with a double stacked PST at ~500mm focal length using a 4 degree tilt Thorlabs wedge prism with a PGR Chameleon 3 USB camera.  If you look carefully at the full size version of the image you can see the left hand side of the image is softer than the right, a result of the tilt which would not be apparent with the Daystar method.

Other alternatives that have been used with some success are the use of atmospheric dispersion correctors, however these are expensive and add a considerable amount of back focus.  If the 1.25" - C mount adaptor you own is made of plastic, cross threading this to fit into the camera nosepiece to introduce tilt is an option, but with the usual caveat of focus gradients across the image and also potential vignetting. 

To sum up; Newtons rings is a problem that will always be with solar imagers, however as can be seen above there are a number of solutions.  By far the best method is the Daystar Interference Eliminator, but this is also the costliest, but for the serious solar imager cost should not be the deciding factor.  For those not wanting to spend any money flat fielding can be effective within reason and limitations.  For those wanting to spend some money, but not prepared to pay the premium of the Daystar route, for me, the wedge prism followed by the 'standard' tilt adaptor are the options to follow.

Saturday, 5 November 2016

CaK Full Disk 5th November

It may well be fireworks night here in the UK, but there are no fireworks on the sun at the moment, with a virtually blank disk other than a couple of areas of plage and a single very small sunspot.  Even the prominences were very small scale and barely visible.  The sun is getting very low in the sky now as we head into november and it won't be long until my viewing window is very limited.  Taken with the 40mm scope at 500mm focal length with the homebrew CaK filter and the PGR Chameleon 3 camera.