Sunday, 4 December 2016

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.

Sunday, 16 October 2016

Ha Full Disk - 16th October

Just the one image from today as seemed to be under a cloud streamer, and then the sun passed into the trees.  Still work to be done with this PST, there is soooo much slack in the threads in the etalon tuning ring that it is difficult to fine tune; next steps are some PTFE tape on the threads.  Secondly the eyepeice holder will be reduced in length so that i'm not at the extremes of focus with the camera.  Either way, all good fun playing.  Taken with a Lunt50 to double stack it and a PGR Chameleon 3 camera. Tilting to get rid of newtons rings causes the right hand edge to be a little soft, but I have on order a wedge prism to go in the camera nosepiece as a possible solution - stay tuned for updates on this over the weeks!

Saturday, 15 October 2016

Saturdays Trifecta - 15th October

The trifecta of solar images is at the heart of the Brierley Hill Solar logo, and it seems like ages since i've done one, so, today seeing as I imaged in 3 wavelengths I decided to put one together!  All taken with 40mm aperture, 500mm focal length and a PGR Chameleon 3 camera.

Ha Full Disk 15th October

The double stack disks are back!  I decontacted an etalon in my trusty DS40 scope earlier this year, and despite recontacting the damaged etalon, i've never been enamoured with the results it gives.  As such there has been a period of drought while I sought another solution.  Here it is, a double stacked PST; with a difference.  Firstly it is double stacked with a Lunt 50 etalon, just to be different, and the bf5 has been replaced with a bf10 as this has better contrast and light throughput, it also allows me to move the disk such that the sweetspot is central on the disk.  Still work to do here, I think the etalon tuning assembly can be tightened up to lose a bit of slack, and also the black box at the back can also be replaced with a 'less glass' solution.  There is ofcourse the possibility of triple stacking, but that's down the road, the first step is to fine tune the double stack.

CaK Full Disk 15th October

The proms were quite easy to see today in CaK light due to the clean air following the passage of a weather front and the deep blue skies in the suckers gap that followed.  Taken with the 40mm scope at 500mm focal length with the home brew CaK filter and PGR Chameleon 3 camera.  Despite the sun being relatively spot free there was plenty of white plage on view.

Whitelight Full Disk 15th October

A rather quiet full disk today, not many active regions at all.  Big round bunnies caused by chips in my solar continuum filter - must get a new one!  Taken with the 40mm scope at 500mm focal length and the PGR Chameleon 3 camera with a ND3 filter over the aperture of the scope.

Wednesday, 12 October 2016

AR12599 in Whitelight - 9th October

There was lots of subtle detail visible in this whitelight shot of this nice little active region taken with the Tal100R refractor, Lunt solar wedge and the PGR Chameleon 3 USB3 camera.  I've been quite pleased with the whitelight shots taken from this session, i've not done any white light for a while, might have to try some more again when there are some nice spots to look at!

AR12599 in CaK - 9th October

Stopping the aperture down from 100mm to 80mm helped to tame the poor seeing on sunday 9th, but it is difficult to make out the penumbral fibrils, which when visible is always a indication of better conditions.  Taken with the home brew Cak filter and the PGR Chameleon 3 camera.

AR12598 in Whitelight - 9th October

The longer wavelengths of whitelight are much less susceptible to the effects of the poorer seeing than the calcium images are, and has been a while since i've done any white light, and are pleased with the results.  Taken with the 100mm Tal100R refractor at 2000mm focal length with the Lunt Solar wedge and the PGR Chameleon 3 camera.  

AR12598 in CaK - 9th October

Even with the Tal100R stopped down to 80mm the seeing was too much at 2000mm focal length, giving quite a soft feel to the image.  Need to try a wedge prism with the PGR Chameleon 3 to see if it helps with the Newtons ring.  Still, a lot of nice bright white plage around this active region.

Tuesday, 11 October 2016

AR12600 in Whitelight - 9th October

This spot really isn't doing very much, but I was pleased with this image taken with the Tal100R refractor, the Lunt solar wedge and the PGR Chameleon 3 camera.  

AR12600 in CaK Light - 9th October

Using the 100mm Tall00R and a 2x barlow was really struggling in the seeing conditions, but with declining solar activity and the sun sailing southward below the celestial equator in the autumnal time of year it is important to just image what you can get!  Taken with the homebrew CaK filter and the PGR Chameleon 3 camera.

CaK Full Disk 9th October

The 40mm scope running at 500mm focal length really is effective in producing these CaK full disks with the home made CaK filter and the PGR Chameleon 3 USB3 camera.  It's nice to see some decent activity on the face of our star!

Ha Full Disk - 9th October

Messing around here with a Lunt50 etalon double stacked on a PST.  Tuning was not easy, the PST etalon seems stiff to tune and so a little more investigation is required to tweak, but, this setup seems to have some potential!  PGR Chameleon 3 camera was used.

Sunday, 2 October 2016

AR5455 Ha Animation 2nd October

It really was pushing things with the poor seeing conditions using the 203mm Airylab HaT, with a low sun, rising morning temperatures as we head into October.  Still, I persevered and did an animation spanning just over 10 minutes in length, it shows well the poor seeing, but also the waving pampas grass like motion of the solar plasma.  The etalon was the double stacked Daystar Quark and the PGR Blackfly GigE IMX249 camera.  

S5455 Ha Closeup 2nd October

This as yet un-designated region on the sun was quite possibly the most active part of the sun today.  With the HaT there was a hint of a spot emerging, and the bright plasma and twisted filaments indicate a more active magnetic field associated with it.  Taken with the Skywatcher ED80, double stacked Daystar Quark, a Baader solar telecompressor to give a reduction factor of 0.75x, and the PGR Chameleon 3 camera.

Western Prominence - 2nd October

There was a lovely prominence visible on the western limb of the sun today.  Looking online it was quite dynamic and fast moving, and was a shame there was quite a lot of cloud coming through else I would have attempted a time lapse.  Taken with the Skywatcher ED80, Double stacked Daystar Quark and the PGR Blackfly GigE IMX249 camera along with a Baader Solar telecompressor to try and make the most of the poor seeing conditions.  

Southern Polar Crown - 2nd October

The one feature of interest on an otherwise relatively blank disk today was this seemingly innocuous solar polar crown.  This cloud of cool plasma is held aloft above the solar surface by magnetic fields that outline the boundary of gigantic unipolar cells near the poles.  Taken with the Skywatcher ED80, double stacked Daystar Quark and the PGR Blackfly GigE IMX249 camera.

S5452 Ha Closeup - 2nd October

This un-designated region in the face of the sun appears to be a small emerging flux region, whether it develops into anything more sizeable remains to be seen.  Either way the 203mm Airylab HaT is a superb piece of kit for revealing these smaller areas of activity on our star.  Taken with a double stacked Daystar Quark etalon and a PGR Blackfly GigE IMX249 camera.

S5456 - Ha Closeup

This was one of the undesignated areas on the sun today that showed up well with the 203mm Airylab HaT.  A small area of plage.  Taken with the Double stacked Daystar Quark and the PGR Blackfly GigE IMX249 camera.  

Only Plage - 2nd October

NASA was reporting a spot less disk today, and as we head towards solar minimum such days will become more and more common.  Looking at 393nm in CaK wavelengths while things are still quiet, the sun is not completely blank, with white plage - magnetic froth being visible in a number of regions on the suns disk.  These correspond to areas of magnetic activity, just not of sufficient field strength for spot formation to occur.  The seeing was not good this morning, with a near ground frost the night before and the day heating up quickly.  This was taken with the Tal100R refractor at 1000mm focal length with the home brew CaK filter and the PGR Chameleon 3 camera.

CaK Full Disk 2nd October

With these wide angle views of our star, for me things were more interesting in CaK wavelengths, with the bright white plage indicating relic areas of activity, either emerging or decaying, more likely the latter.  Taken with the 40mm ota at 500mm focal length with the home made CaK filter and the PGR Chameleon 3 camera.  There are hints of todays proms at 3 o'clock visible on the edge of the disk.

Ha Full Disk 2nd October

The disk is very quiet today, no real active regions, but a couple of nice proms at least!  Taken with a Lunt 50mm etalon at ~500mm focal length with a PGR Chameleon 3 camera.  

Monday, 26 September 2016

AR12597 in CaK - 25th September

This is the only activity to speak of on the sun at the moment, and with a decaying magnetic field no longer poses a threat for any M-class flare activity.  Taken with the Skywatcher ED80 stopped down to 60mm at ~1400mm focal length with the homebrew CaK filter and the PGR Chameleon 3 camera.

AR12593 in CaK - 25th September

Not much other than a region of decaying plage is what can be seen here in this active region as it headed towards the limb in this image taken with the Skywatcher ED80 stopped down to 60mm at ~1400mm focal length with the homebrew CaK filter and the PGR Chameleon 3 camera.

Cak Full Disk - 25th September

The seeing conditions were awful on sunday afternoon were awful in the unstable air following the passage of a cold front, but at least they offered clear skies, and, with the seeming distinct lack of good weather lately you have to make the most of every opportunity.  The disk was surprisingly blank in CaK light, with a area of place passing towards and over the western limb, and a small active region with some small spots just off mid disk.  Taken with the homebrew CaK filter, 40mm scope at ~500mm focal length and the PGR Chameleon 3 camera.