Processing…

No-one is getting out much for astrophotography in Cumbria at the moment, as we are seeing endless cloudy skies.  Plenty of time to practise processing.

I made it up to my favourite dark lay-by near Tebay on 23 November and captured an hour of the Andromeda Galaxy M31.  29 frames of two minutes each.  If you’re wondering what a single two-minute frame looks like, here is one.  This is what you get if you open the shutter on your camera for two minutes.  The darkness of the background shows what an excellent location it is on the remote country road.  I’ve not done any processing on this frame, just converted it to jpeg for display here.

_DSC0020

300mm lens @ f/5.6 on Nikon D90 @ ISO 1600

Stacking the 29 frames and applying the usual processing tricks of adjusting the background, stretching the histogram, and a little colour saturation boost, gives this:

integration_DBE_Stretch

M31: 300mm @f/5,6, ISO 1600, 58 minutes
29 frames of 2 minutes.

That’s a shot I’ve wanted for a long time.  M31 nicely framed through a 300mm lens.  What more can we do with this?  Well, today’s lesson is all about High Dynamic Range “HDR” transforms: re-stretching the brightest parts of the image to bring out further detail.  Pixinsight, my chosen processing software, permits this:

integration_DBE_Stretch_HDR6

M31: 300mm @f/5,6, ISO 1600, 58 minutes
29 frames of 2 minutes
HDR transform

The effect of this adjustment is noticeable at the centre of the galaxy, where previously the detail had been hidden by the excessive brightness.

I’m also on a mission to use every scrap of data I can gather on M31, and Pixinsight also allows me to re-scale last year’s frames (taken through a 200mm lens at 5 minutes per exposure) and amalgamate them with the current set of 300mm frames.  Here’s the combined set, processed as normal:

200+300

M31: 300mm @f/5,6, ISO 1600, 58 minutes
29 frames of 2 minutes
Plus: 200mm @ f/f.6, ISO 200, 40 minutes
8 frames of 5 minutes

 

Next, the combined set with the HDR transform pushed hard to enhance the detail in the spiral arms of the galaxy:

Transformed

M31: 300mm @f/5,6, ISO 1600, 58 minutes
29 frames of 2 minutes
Plus: 200mm @ f/f.6, ISO 200, 40 minutes
8 frames of 5 minutes
HDR transform

 

I could be happy with that, but it’s quite hard on the eye, so I layer the original and the transformed versions together in Photoshop, which gives us the best of both worlds.

200+300layered

M31: 300mm @f/5,6, ISO 1600, 58 minutes
29 frames of 2 minutes
Plus: 200mm @ f/f.6, ISO 200, 40 minutes
8 frames of 5 minutes
HDR transform layered over original

There’s still a long way to go with this.  I’d like to take longer exposures without the stars trailing, and so get finer detail in the outer reaches of the galaxy’s arms.  Even at two minutes through the 300mm lens, the stars trail by a couple of pixels or so.  A couple of pixels doesn’t really matter for stars (they just appear slightly elongated rather than perfectly round) but it matters a great deal for the fine detail in the arms of the galaxy.

Supernova SN 2014J in M82

This is one of those quite gratifying occasions when a major discovery in the sky falls within the relatively easy reach of the amateur astrophotographer.

On 21 January, astronomy news feeds were reporting a supernova becoming visible in galaxy M82, close to the constellation of Ursa Major. Here in Kendal, we hadn’t seen much of the night sky since November, but on the night of 22 January, I looked out of the back door just before bedtime and saw clear skies with only the occasional cloud blowing over. An hour invested here would probably bring rich rewards.

In about five minutes I had managed to set up the mount, polar align, balance and focus the 300mm AF-Nikkor (on a conveniently placed Jupiter – that autofocus is a gem!). The next 20 minutes were spent in all sorts of contortions trying to find M82 in the viewfinder. I had set the tripod very low, to minimise vibration, and M82 was very high in the sky. That’s easy with a right-angle viewer on a telescope, less easy in a camera viewfinder. M82 is invisible to the naked eye, so each reframe needed a fresh exposure of about a minute to confirm, but the more frustrating problem was that M82 is so close to the celestial pole that minor adjustments of the mount go off in unexpected directions.

Once found and centered, I managed four reasonable frames of two minutes each before the clouds closed back in. Rather than stack using the usual software, I combined these as simple layers in Photoshop, boosted the contrast a little and tuned out the worst of the background glow of Kendal’s street lights.

About a year ago, I had shot M82 and its more circular companion M81 as a short experiment to mark a galaxy pair that I’d like to image later in more detail. Here is last year’s image, without the supernova (using the old manual 300mm lens):

M82 no nova

M81 and M82, 1 March 2013
300mm f/5.6, ISO 400 30 minutes.
10 frames of 3 minutes.

Then the current image with the brand new dot in M82 (new lens, same focal length, better glass):

M82 nova

M81 and M82, 22 January 2014
300mm f/5.6, ISO 400 8minutes.
4 frames of 2 minutes.

I say brand new, but this galaxy is about 11 million light years away, so this event happened a long time ago and the news has taken a while to reach us.

Before, and after. Not bad for an hour in the back yard between the clouds.

…and for those who couldn’t spot the difference, here it is!

PS layered.jpg

 

Chasing ISON through the clouds – the full story of early morning 15 November 2013

To say that astrophotography in Cumbria is “hit and miss” would be an understatement.  It is mostly miss.  Cumbria, home to The English Lake District, is probably the wettest county in the UK.  When we are not catching the wet weather fronts coming in every few days from the Atlantic, the terrain tends to generate its own weather system, which is likewise cloudy and wet.  This forecast is not untypical:

0010 forecast

Against this backdrop, my astrophotography is based on a simple (EQ3-2) equatorial mount, an RA motor with rechargeable batteries, and my trusty Nikon D90 with a small collection of reasonably good lenses.  My favourite piece of kit at the moment is the WiFi SD card, which means I can review shots immediately on the iPad rather than on the back screen of the camera.  The temptation of further investment in hi-tech astrophotography kit is a constant companion, but yielding would only serve to heighten the frustration (by increasing the sunk cost) of all those cloudy nights.

0020 mysetup

I guess it follows that every outing is tempered with fairly low expectations, as conditions can appear good, then change at a moment’s notice.  On this particular night, my expectations were on the low side – the forecast of “clear intervals” and humidity around 90%, were not very encouraging for a target low on the horizon.  However, my good friend Stuart Atkinson from the Eddington Astronomical Society had texted the previous evening and persuaded me to set my alarm for 3.30am, so I set about planning for our excursion.

My plan for all sessions follows the same rules: (i) examine the star chart to plan the frame and check the timetable, (ii) go to the chosen location and set up whatever the prospects, (iii) don’t be disappointed if the forecast is wrong.

Get the idea?  How I envy those with reliable clear skies!

Rule number one, check the star chart.  On the morning of 15 November, ISON would rise at 04:05 and astronomical twilight would begin at 05:34.  That meant a window of 89 minutes, but for the first 40 of those ISON would be below 5 degrees.  Okay, set up and be ready by half past four, leaving an hour for capture.

At 03:30 the alarm goes off and a quick glance through the curtains suggests a “reasonable” sky.  Load the car, drive past Stuart’s to collect him, then off we go to the east of town where there is a good view to the eastern horizon across open countryside.  There is a small hill which, viewed from my observing spot, is perfectly shaped and positioned so that the ecliptic glides up above the left-hand slope.  I have used this location several times over the last month or so.

When we arrive and take a look, I realise to my embarrassment that the ecliptic has moved south since my last excursion, and is now behind the hill.  Oops!  Stuart politely mutters something about “a mistake anyone could make” as we jump back in the car and head for the next best situation, a small car park about a mile further north.  Unfortunately this car park is on the western side of the main road, so by looking east we will have to put up with the headlights from any pre-dawn traffic.

There is a bank of cloud on the eastern horizon, but it looks to be quite mobile.  Rule number two kicks in – always set up the mount and point the camera in the right direction.  If conditions improve, there might not be time to set up later.  My routine is sufficiently well practised that I can unload the mount from the back of the car and be polar aligned well enough for five-minute exposures at 300mm focal length in just a few minutes.  As always, I use the tripod unextended for stability, which means kneeling down to squint up through the polarscope while holding a small red torch to illuminate the reticle.  In a couple of minutes, Polaris is sitting nicely in the hole and I can clamp the camera to the mount.

So where’s ISON then?  I have memorised this grab from the star chart:

0030 star chart

That’s my camera frame on Porrima, in the constellation of Virgo, set at 4.5 x 3.0 degrees for the 300mm lens.  If I place Porrima in the top right corner of the frame, then slide exactly one frame down the declination axis, ISON will be in the bottom left corner.  So where’s Porrima?  Here’s the first test shot:

0040 Porrima

Porrima top right, then slide one frame down and…

0050 Where?

Cloud.  My eye is drawn to the smudge dead centre.  I now know this to be elliptical galaxy NGC 4697, but in my mind ISON will look like a smudge, and there’s a smudge dead centre.  I start to doubt my calculation and my preparation to such an extent that I miss the comet lurking behind the cloud at bottom left – exactly where it should be.

Back to Porrima, slide down the Dec axis again, that didn’t feel right, do it again, nudge it a little bit further (why did I do that?), wait a moment for the clouds to move, and grab another test shot.  All this while chatting with Stuart about clouds, traffic, whether our luck will change, whether it was worth it anyway, and suddenly…

0060 First sight

What on Earth is THAT???  I stop chatting while my brain struggles to reorganise all my expectations in the light of this capture.  It takes several seconds for the realisation to hit home – on all previous occasions ISON has been invisible in the viewfinder, invisible in binoculars, invisible even in small telescopes.  The best so far has been a faint smear in the camera frame, gathered at high ISO and long exposure.  I let out a long whispering sigh of “Ooooooooohhhhhh Gotcha!” and walk the few steps in silent anticipation to show Stuart the iPad image.  What the …..? Take a look at that, my friend, we’ve got ourselves a comet.  Suddenly we are like excited schoolboys, chuckling, giggling, I even dance a little soft shoe shuffle in celebration.  Now we start shouting at the clouds, there must be a gap coming soon?  I hurry to realign the camera very slightly and catch ISON mid frame…

0070 C:2012_S1_20131115_0511

Dead centre.  Perfect.  Only the one frame, then the clouds fill the gap.  For a moment I rejoice in my good fortune to be in the right place, at the right time, camera mounted and pointing in the right direction, mount aligned well enough for this 30 second exposure (yes, this version has been calibrated with dark and flat frames in PixInsight, and histogram stretched to improve contrast and minimise the urban glow on the clouds, but it’s still a single frame).  Then I remind myself it’s not good fortune, is it?  It’s thinking, planning, preparing and practising.  It’s taking notes of every previous comet shot and thinking how the camera, lens and exposure settings influenced the final picture.  Let’s not forget all the nights of going out and coming home disappointed.  It’s setting that alarm clock again and actually getting up, loading up, going out, setting up, being ready, waiting for the moment, and pressing the shutter.  Yes, pressing the shutter!  I hadn’t even set up the remote trigger when this gap appeared in the cloud.  This one, I took by hand.

There must have been hundreds of photos taken of ISON around the world that night, and many more in the weeks surrounding perihelion.  Some of these have revealed exquisite detail in this visitor to our skies, not to mention the contribution they make to scientific data gathering.  Anyone stumbling upon this photo in that context, will probably give it no more than a few seconds then click on by.  It’s really not that good, but… it’s mine.  I took it with my trusty Nikon and an old 300mm lens.  I can even see some detail in the tail.  All those nights of practice and rehearsal chasing PANSTARRS paid off.  After ISON had its outburst on 14 November, we were mostly clouded over.  Then the full Moon filled the night sky with light, and a few days later, ISON had its fateful rendezvous with the Sun.  This particular photo opportunity will never come round again.  From where I live, this might have been the one gap in the clouds that allowed one good shot of ISON between outburst and perihelion.  One chance, one shot, and I got it.

PS. More practice with PixInsight and stacking the other frames I took that morning, has culminated in this version, which I don’t expect to improve.  The embedded credit was added, if I might be permitted a name-dropping little boast, at NASA’s request so that they could circulate it in their outreach work.  That’s the cherry on the icing on the cake.

2013Nov15_SWhite_Adler

Lovejoy and ISON under clear sky

Only nine days from perihelion, ISON is lower and lower on the eastern horizon.  On Monday night (Tuesday morning, of course) I set the alarm for 3.30 and went out to chase it down at a new location, about a mile south of Killington Reservoir, east of Kendal.

It turned out to be a perfect location for looking east, with almost no urban glow on the photos.

Comet C/2012 S1 (ISON) 300mm f/5.6, ISO 400 150 seconds. 5 frames of 30 seconds.

Comet C/2012 S1 (ISON)
300mm f/5.6, ISO 400 150 seconds.
5 frames of 30 seconds.

It is almost impossible to process out the combination of moonlight and early twilight, while retaining the detail in ISON’s tail.  The angular separation of ISON from Spica (top right corner) is about 4 degrees, and others have photographed ISON with a tail in the region of 6 degrees.

Comet C/2012 S1 (ISON) 300mm f/5.6, ISO 400 420 seconds. 7 frames of 60 seconds.

Comet C/2012 S1 (ISON)
300mm f/5.6, ISO 400 420 seconds.
7 frames of 60 seconds.

A little more tail detail comes out from this stack of 60-second frames.  I am using ISO 400 to avoid completely burning out the centre of the comet.

Comet C/2013 R1 (Lovejoy) 300mm f/5.6, ISO 400 180 seconds. 12 frames of 15 seconds.

Comet C/2013 R1 (Lovejoy)
300mm f/5.6, ISO 400 180 seconds.
12 frames of 15 seconds.

Well above the horizon, and unaffected by the twilight, is Comet Lovejoy.  This was a particularly pleasing result, given the bright moonlight.

ISON outburst

ISON observers had begun to report an “outburst” that might have increased  the comet’s brightness by up to two orders of magnitude.  While it is advisable to temper one’s enthusiasm with the knowledge that Cumbrian skies don’t always play ball with astrophotography, my trusty forecaster App indicated that there might be a short window this morning between ISON’s rising at 04:04 and the development of an overcast dawn from twilight at 05:34.

Alarm set for 03:30, swap texts with Stuart Atkinson at 03:40, load the kit in the car and off we go towards Farleton, east of Kendal, to get away from urban lights.

Remember that Cumbrian skies don’t play ball?  Well, there was a stubborn bank of low cloud on the eastern horizon (Stuart’s wider angle photos give a much better context of our session) but suddenly, in the gaps…

Comet C/2012 S1 (ISON) 300mm f/5.6, ISO 800, 30 sec. Single frame.

Comet C/2012 S1 (ISON)
300mm f/5.6, ISO 800, 30 sec.
Single frame.

Amazing for a single shot, compared with the stack of 20 frames from the previous outing.  Note also that this is 30 seconds at ISO 800 whereas the previous outing was 20 x 60 seconds at ISO 1600.  I have stretched the histogram in PixInsight, and rebalanced the colour to get rid of the more extreme red glow in the clouds.

The 12MP frame can even stand cropping to enlarge it to 6x the original…

Comet C/2012 S1 (ISON) 300mm f/5.6, ISO 800, 30 sec. Single frame, cropped.

Comet C/2012 S1 (ISON)
300mm f/5.6, ISO 800, 30 sec.
Single frame, cropped.

Eddington and comets

Members of the Eddington Astronomical Society met at Kendal Castle early on Sunday morning (was that really only yesterday?), to have a look for comet ISON.  There was a good turnout, which meant my photography session wasn’t quite the lonely vigil it usually is. I guess that was down to the presence of the Discovery Channel who are making a documentary about comet hunting, organised through our society Secretary the tireless astronomy outreacher Stuart Atkinson.  To be honest, I was really only there to boost the numbers, as I didn’t think the seeing would be too good – the forecast was well over 90% humidity.

But the humidity wasn’t too bad, especially in our elevated position up Castle Hill, and it was great fun to be staring at the sky with friends for a change!

For the most part, it made sense to stick with the 6 x 60-seconds at ISO 1600 on the new 300mm lens at f/5.6.  I have the dark frames and flat frames for this combination already on file.

First up, comet Lovejoy, very easy to find at an elevation of 54 degrees, well above the mist, and just north of the Beehive Cluster in Cancer.

Comet C/2011 W3 (Lovejoy) 300mm f/5.6, ISO 1600, 6 x 60 sec.

Comet C/2011 W3 (Lovejoy)
300mm f/5.6, ISO 1600, 6 x 60 sec.

 PixInsight allows stacking on the comet centre, so the starts are slightly trailed.

Then on to ISON, by star-hopping from Regulus through Mars straight down the ecliptic.

Comet C/2012 S1 (ISON)
300mm f/5.6, ISO 1600, 6 x 60 sec.

ISON doesn’t present as well as Lovejoy, owing to its position nearer the horizon.

That went well, so a quick trip over to LINEAR, rising next to Arcturus.

Comet C/2012 X1 (LINEAR) 300mm f/5.6, ISO 1600, 6 x 60 sec.

Comet C/2012 X1 (LINEAR)
300mm f/5.6, ISO 1600, 6 x 60 sec.

LINEAR doesn’t look anywhere near as good as last week’s capture.

After that, I left the camera running, for twenty more frames of ISON.

Comet C/2012 S1 (ISON) 300mm f/5.6, ISO 1600, 20 x 60 sec.

Comet C/2012 S1 (ISON)
300mm f/5.6, ISO 1600, 20 x 60 sec.

These have processed quite well in PixInsight to remove most of the sky glow. I might return to these frames and see if I can’t eliminate more of that background colour. I’d also like to try putting the comet back onto a set of frames stacked on the stars.