PANSTARRS one more last time… (actually two)

The night after my encounter with the noctilucent clouds, we were again presented with a clear sky in Cumbria.  I decided to have a last go at the increasingly remote target of PANSTARRS from my back yard, not exactly the darkest of sites.  Next door is a small hotel, and the all-night corridor light is behind a window with no curtain.  There is some intrusion from the street lights, and when the council staff in the offices behind the house leave for the night, they often leave the lights on.  Finally, if the Fire Station or Ambulance Station do their night test drill, there can be every kind of light pouring into the yard.

However, a clear forecast tempted me to try setting up the system and leaving it running all night.  A guarantee of no rain convinced me this would be okay.  Of course, only the middle part of the night would be even vaguely dark (the Sun would never be more than 13 degrees below the horizon), but at least I would fill that darkish hour with frames and not have to stay up all night.

Balancing the RA axis of the mount took on a new importance.  Remember, this is a second hand EQ3-2, tracking but unguided.  Normally I would set the counter weight in an optimum position and ensure it was slightly heavy against the turn of the motor, using a ball & socket mount to retain flexibility in camera direction and orientation.  One of the advantages of sitting by the system while gathering shots, is that the RA axis can be moved back to the optimum position.  Leaving it running all night meant that the optimum had to survive about six hours or more.

300mm f/5.6, ISO 3200 5 min.

300mm f/5.6, ISO 3200 5 min.

This is a JPEG of the unprocessed RAW frame from about 1am.  You can see how much background light needs to be eliminated.  The level of humidity in the air made this an extremely difficult task.

300mm f/5.6, ISO 3200, 15 x 5 min.

300mm f/5.6, ISO 3200, 15 x 5 min.
15 frames stacked in DSS on both stars and comet.

Deep Sky Stacker (“DSS”) lets you stack the frames by reference to the stars, or the comet, or both.  In stacking for both, DSS makes two separate stacks.  It then selects the stacked comet (eliminating the accompanying star trails) and inserts it in the reference frame for the stacked stars (eliminating the accompanying trailed comet).  A significant loss of quality results, probably not helped by the humidity in the air.

Picture saved with settings applied.

300mm f/5.6, ISO 3200, 15 x 5 min.
15 frames stacked in DSS on the comet.

Stacking only on the comet avoids this loss of quality – and retains a more dynamic feel to the picture, in my view, showing clearly that the comet is moving against the star background.  This is my preferred setting, and my favourite shot of this page.  The tail is slicing past Yildun (Mag 4.3), some 2 degrees 33 minutes of arc away.  Given that PANSTARRS is 1.86 AU away from Earth in this photo, that angle represents about 12.4 million kilometres, and the visible tail must therefore be about 15 million kilometres long.  Visible, that is, at 5 minutes exposure.  At Mag 9.5, PANSTARRS is invisible to the naked eye.

I wondered whether the choice of ISO 3200 was excessive.  The comet’s core is burned out on the screen, and there is little dynamic range in the picture.  Three nights later, I got a second chance at the same experiment.  This time I reduced the ISO to 400, and the humidity in the night air was a little lower anyway.

300mm f/5.6, ISO 400, 5 min.

300mm f/5.6, ISO 400, 5 min.

This is a sample unprocessed frame from about 1am again.  This time, I stacked only the 11 frames from the darkest hour.

300mm f/5.6, ISO 400, 11 x 5 min. Stacked on stars and comet.

300mm f/5.6, ISO 400, 11 x 5 min.
11 frames stacked in DSS on stars and comet.

The quality of the result is still very hard to control when stacking on both stars and comet, but there is a definite improvement in dynamic range compared with the ISO 3200 version.  That’s Urodelus (Mag 4.2) in the bottom right corner, by the way.

300mm f/5.6, ISO 400, 11 x 5 min. 11 frames stacked in DSS on the stars alone.

300mm f/5.6, ISO 400, 11 x 5 min.
11 frames stacked in DSS on the stars alone.

Stacking on the stars shows the comet’s movement, but blurs its important detail.

300mm f/5.6, ISO 400, 11 x 5 min. 11 frames stacked in DSS on the comet alone.

300mm f/5.6, ISO 400, 11 x 5 min.
11 frames stacked in DSS on the comet alone.

Stacking on the comet reveals its movement against the stars in a more dynamic way.  As for the reduced ISO, I think the dynamic range might be better, but there is less information overall.  On balance I prefer the ISO 3200, which is not surprising for a Mag 9.5 object using 5-minute subframes.

Anyway, the kit survived being left out all night, for two nights, which bodes well for when the nights get longer again.  That is definitely my last attempt at PANSTARRS.  It has been great fun, with cloud dodging, high humidity and low altitude at the key stage of passing M31, followed by increasingly light nights as it climbed towards the celestial pole.  It best, it has been a joy to watch and to capture.  Even at its most frustrating, it has given me bags of practice and experience to fall back on when ISON arrives this autumn.

PANSTARRS through floodlights in the sky

Inspired by several astrophotographers around the world posting images of the amazing tail developing on PANSTARRS, I decided to have another go at this comet.  There is a minor road / very long layby running parallel to the A591 on the hill between Kendal and Staveley, with unimpeded views to the north.  I reckoned it would be almost as good as driving into the Kentmere valley.

En route, I dropped by Helsington Church again, to see how the planetary alignment was changing over the Langdales.  Jupiter, Venus and Mercury were now in a straight line and all clearly visible.  I met a delightful family who had come to look at the sunset after spending the day in Kendal, and we passed such an enjoyable half hour with my binoculars spotting planets that I forgot to take photos.

On to the layby, and quite easy to set up with Polaris visible in almost enough twilight to see the mount dials.  Hold on though, that northern sky is getting brighter, not darker!

18mm f/3.5, ISO 1600 1 sec.

18mm f/3.5, ISO 1600 1 sec.

Yes the noctilucent cloud season is under way.  I can’t make up my mind about these clouds that are only visible at night – is this astronomy or meteorology?  Yes, they are really pretty to look at, with amazing variation and complexity in their structure, but that’s Cassiopeia up there, and my dark sky location is ruined.

18mm f/3.5, ISO 1600 1 sec. Two High Pass filters: 40 pixels and 4 pixels.

18mm f/3.5, ISO 1600 1 sec.
Two High Pass filters: 40 pixels and 4 pixels.

Sharpened in Photoshop, the structure resembles waves on a beach.

Prompted by a comment on Noctilucent Clouds 2013, I have experimented with sharpening these images using two Photoshop techniques: Unsharp Mask and High Pass Filter.

NLC plain

50mm f/8, ISO 1600, 3 sec.

The unsharpened image.

NLC USM 200% 4P

50mm f/8, ISO 1600, 3 sec.
Unsharp mask 200%, 4 pixels.

Unsharp mask – Photoshop’s main choice of sharpening tool, but the effect can be seen across the whole image.

NLC HP40SL HP4HL

50mm f/8, ISO 1600, 3 sec.
High pass filter 1: 40 pixels, soft light blend.
High pass filter 2: 4 pixels, hard light blend.

High pass filter – this sharpens only regions of higher contrast ie edges, that benefit from sharpening but leaves the rest of the image untouched.  I picked up this tip from Nik Szymanek in a workshop at the International Astronomy Show in Leamington.  Nik was using it to enhance detail in galaxy images, but the principle applies just as well to noctilucent clouds.  I prefer this sharpening effect which doesn’t introduce the “sharpened feel” artefact to the whole canvas.

Anyway, eventually the light fades and I catch seven reasonable frames of PANSTARRS.

PANSTARRS passing Mag 4.3 Yildun and its Mag 5.8 partner "24 Ursa Minor". Yildun is the next star to Polaris in the tail of Ursa Minor. 200mm f/5.6, ISO 3200 7x3min.

PANSTARRS passing Mag 4.3 Yildun and its Mag 5.8 partner “24 Ursa Minor”.
200mm f/5.6, ISO 3200 7x3min.

Yildun is the next star to Polaris in the tail of Ursa Minor.

North is to the lower left of the shot, and the glow from the pesky noctilucent clouds can be seen in the comet’s tail – which is pointing pretty much towards the Sun.  I shouldn’t really moan about the cloud, as the Sun is only 13 degrees below the horizon so it’s not exactly dark anyway (from an astronomical point of view).

PANSTARRS one last time?

This is an awkward time of year for astrophotography. It only gets really dark after the end of “astronomical twilight”, when the Sun dips 18 degrees below the horizon. That didn’t happen until quarter past midnight last night, and by 2am it was back above that 18 degree line. The longest day / shortest night is still six weeks away, so for the next twelve weeks the night sky will be at least as testing as it is now.

These photos were taken in the hour around 1am last night, from the long layby set back from the A591 east of Staveley.

First, the constellation Cepheus:

PANSTARRS approaching Cepheus 50mm f/5.6, ISO 800, 15 min. Single frame of 15 minutes.

PANSTARRS approaching Cepheus
50mm f/5.6, ISO 800, 15 min.
Single frame of 15 minutes.

The 50mm lens gives a 27×18-degree field of view on the D90, so just enough space to accommodate the whole of Cepheus as PANSTARRS (mag 7.2) approaches from Casseopeia.

At ISO 800 all the numbered stars in Cepheus are fully illuminated on the screen, including Erakis (mag 4.1), the “Garnet Star” on the right.

On to PANSTARRS with the 300mm lens:

PANSTARRS approaching Cepheus 300mm f/5.6, ISO 800, 8 min. 2x4 min. frames stacked in Photoshop.

PANSTARRS approaching Cepheus
300mm f/5.6, ISO 800, 8 min.
2×4 min. frames stacked in Photoshop.

PANSTARRS approaching Cepheus 300mm f/5.6, ISO 800, 8 min. Single 8-minute frame.

PANSTARRS approaching Cepheus
300mm f/5.6, ISO 800, 8 min.
Single 8-minute frame.

Two questions are answered here. First, does a stack of two 4-minute frames deliver more than a single 8-minute frame (all other settings unchanged) or is it the other way round? Decide for yourself, but I think there’s more refinement in the layered 4-minute frames and more punch in the single 8-minute frame.

Second, can the EQ3-2 mount track accurately for 8 minutes loaded with the D90 and a 300mm lens? Looks good to me.

At 2am it’s getting light in the east (!!) so time to pack up. I’ve had great fun photographing PANSTARRS over the last few weeks and learned many lessons along the way, but this is probably the last session, given the combination of short, late nights and uncertain Cumbrian weather.

PANSTARRS success from Kentmere

Tuesday 30th April was sunny all day, the last patches of cloud drifting away to the north in late afternoon.  After my previous encounter with humidity and moonlight in Kentmere, it looked like a good opportunity to test this new dark site.

_CSC0003

This is how my setup looks.  Just me, a layby and the EQ3-2 equatorial mount.  At 9.30pm the Sun has already set, but I wanted to leave plenty of time in case it clouded over and I had to dash to another location.  It will be another couple of hours before the Sun is 18 degrees below the horizon, the offical end of astronomical twilight.

Elevation 25 degrees, Sun is 15.7 below horizon.

Elevation 25 degrees, Sun is 16.2 below horizon.

Elevation 25 degrees, Sun is 16.4 below horizon.

These unprocessed frames with the Sun only 15 degrees below the horizon show what a difference that makes to long exposures.

50mm f/2.8, ISO 800, 6 min. 2 X 240 sec. frames stacked in Photoshop.

50mm f/2.8, ISO 800, 8 min.
2 X 240 sec. frames stacked in Photoshop.

Two frames of 4 minutes each, stacked as layers in Photoshop.  PANSTARRS is in the centre, moving from Cassiopeia to Cephus.  The settings of ISO 800 and 240 seconds were inspired by Fred Espinak’s version, using pretty much the same kit.  I guess the difference in our results is an indication that, even on a good night in Kentmere, conditions in Arizona are better.  The thousands of stars in the bottom left corner (Cassiopeia is in the Milky Way) become so indistinct through our 80% humidity that they look like background glow, and any attempt to eliminate them damages the rest of the picture.  On the other hand, it could just be that Fred is much better at this than I am.

300mm f/5.6, ISO 3200, 12 min.
3 x 240 sec. frames stacked in Photoshop

With the 300mm lens, the optimum aperture is f/5.6 so I have wound the ISO up to 3200 to compensate.  Four minutes tracking with the 300mm lens is quite satisfying, with the stars showing no sign of trail.

PANSTARRS is passing close to two nebulae, Cederblad 214 and NGC 7822, between Cassiopeia and Cephus.  While neutralising the background, I notice that I have caught some nebulosity in Cederblad 214 – that’s the reddish glow to the right of PANSTARRS.

The comet itself still has two distinct tails.  The ion tail points away from the Sun (towards one o’clock in this photo) and the dust tail trails behind the comet (towards nine o’clock in this photo).

300mm f/5.6, ISO 3200, 5 min. Single frame of 300 sec.

300mm f/5.6, ISO 3200, 5 min.
Single frame of 300 sec.

Before packing up, I can’t resist an attempt at a five-minute frame.  The tracking seems to hold up well, which promises much for future sessions.

PANSTARRS in Casseopeia

First attempt, a fairly optimistic shot over the garden fence on 19 April.

Casseopeia with PANSTARRS

18-200mm @ 65mm f/5.6, ISO 1600, 6 min
12 x 30 sec frames stacked in DSS

The clear sky had tempted me to set up the kit, but the urban glow catching the moisture in the atmosphere defeated any serious attempt to produce a reasonable photo. I thought that stacking several frames would help edit out the glow, but it doesn’t work that way.

Out to a new site on 20 April, in a layby part way up the Kentmere Valley.

C&P4x30

50mm f/2.8, ISO 800, 2 min
4 x 30 sec frames stacked in Photoshop

Skies were forecast to clear for an hour or so around midnight, but the waxing gibbous moon spread light throughout the sky. There were a few wisps of low cloud on the northern horizon. These 4 frames were stacked as layers in Photoshop.

My intention was to assess the suitability of the site for views to the north. Having escaped the street lights of Kendal, the next town north from Kentmere Valley is Penrith, some 19 miles away over mostly uninhabited countryside. It was pleasing to see there was almost no discernible urban glow in the northern sky.

C&P4x2

50mm f/4, ISO 800, 8 min
4 x 2 min frames stacked in Photoshop

Finally, four reasonable frames of 2 min each, relatively cloud free. Given that I was able to write notes by the moonlight, and the humidity was high enough for cloud inversion to begin settling in the valley (see bottom right corner of the photo), this is a pleasing result. Certainly I will visit this site again around the New Moon in about a fortnight. Cloud permitting…

M31 and PANSTARRS

When the Cumbrian skies cleared on 1 April we had the opportunity for several nights of catching PANSTARRS in glorious juxtaposition with the Andromeda Galaxy M31.

First up, some test frames on 1 April which turned into a nice capture that I’d had in mind for some time.

50mm f/5.6, ISO1600, 2min 4 x 30-sec frames stacked in DSS

50mm f/5.6, ISO1600, 2min
4 x 30-sec frames stacked in DSS

With a standard 50mm lens and some judicious cropping, this letterbox format shows Mirach (one of the guide stars used when finding M31: “from Mirach, hop right one star, then again, then down to the fuzzy blob”) with M33 faintly visible on the left, M31 on the right and PANSTARRS making its way in from the bottom.

Quite a windy evening, so I cranked up the ISO to 1600 and took just four good frames at 30 seconds.

On to the following night…

200mm f/5.6, ISO 1600, 15 min. 30 x 30 sec. frames stacked in DSS.

200mm f/5.6, ISO 1600, 15 min.
30 x 30 sec. frames stacked in DSS.

Quite breezy again, so I kept the exposures down at 30 seconds, but on the 200mm lens.  30 frames stacked for a 15 minute total exposure.

PANSTARRS is only about 7 degrees above the horizon here.  That presents a whole new set of problems.  At this angle, the line of sight goes through about ten times as much atmosphere as at zenith, multiplying the effect of water vapour on the incoming light.  From this location, Helsington Church, the view North-West also passes over the lights of Windermere and Ambleside, giving a street light skyglow to the bottom of the frame.  One of the beautiful features of PANSTARRS is its fan tail, glowing by reflected sunlight, so any attempt to process out the skyglow tends to eliminate the tail too.

300mm f/5.6, ISO 400, 40 min. 20 x 120 sec. frames stacked in DSS.

300mm f/5.6, ISO 400, 40 min.
20 x 120 sec. frames stacked in DSS.

Another shot I had framed in my mind, estimating there would be just enough room in the 300mm frame to put both M31 and PANSTARRS.  As the wind had dropped, I could get exposure up to 2 minutes, and grabbed 23 frames of which 20 were acceptable.

Finally on 3 April…

200mm f/6.3, ISO 200, 60 min 12 x 5 min. frames stacked in DSS

200mm f/6.3, ISO 200, 60 min
12 x 5 min. frames stacked in DSS

The birthday fairy brought me a polarscope this year, which dramatically reduces the time taken to polar-align the EQ3-2 equatorial mount.  In  a couple of minutes I can align more accurately than I used to get from 30 to 40 minutes of drift alignment using the camera.  Certainly it is good enough for 5 minute exposures at up to 300mm.  I must find time to test the alignment with longer focal length.  Anyway, this stack of 12 frames at 5 minutes each has cropped nicely.  M31 is not as clear as I would have liked (see M31: up to 200mm) but it was too low in the sky for that.

There was another very pleasing alignment on 5 April but the Cumbrian clouds had closed in.