Imaging session: Chasing Comet Lemmon - A night on the Moors

  New to this blog, then welcome, and after reading this post why not stop off here and find out more https://undersouthwestskies.blogspot.com/2025/01/welcome-to-my-new-astronomyastrophotogr.html

To photograph Comet Lemmon under bright moonlight, which was the plan for this imaging session, I intend to use short exposures combined with image stacking and processing software. The bright moonlight (a waxing gibbous moon around 80% illuminated tonight) will wash out fainter details, so I’ll need to compensate with equipment and post-processing. Whilst the weather will be dry for a change, it will be predominantly cloudy with strong breezes and some big old gusts. All the apps are predicting a chance of a clear spell window between 7 – 8pm.

So, in today’s blog post, I

·       Share the story setting of the night

·       Outline how I set up for the shoot

·       List the equipment I used

·       Share the camera settings that worked on the night

In a follow up post, I will share what steps I took to stack and post edit the images collected

As always, if you have any questions, thoughts, tips or photos to share, just drop me a comment in the box at the end of the post.

Let’s dive right in then.

Chasing Comet Lemmon – A Night on the Moors

The wind has teeth tonight.
I’m high on the moors, parked in a puddled, muddy car park, off the Princetown Road — Lowery Cross, a lonely outpost overlooking the dark sweep of the Tamar Valley far below. Out on the horizon, Bodmin Moor rises like a sleeping giant under a blanket of low cloud, Cornwall’s heart beating faintly in the distance.

The sun has long slipped below the edge of the world, and the sky is in that magical in-between — half night, half memory of day. I arrived 90 minutes or so ago to survey the scene and select my final shooting position. I need a really clear view of the western sky just above the horizon and inconveniently high gorse bushes made it tricky to get that perfect view. Now, the stars above are beginning to blink awake, timid at first, then boldly twinkling between ragged ribbons of cloud that scuttle across the heavens.

Behind me, the pine forest whispers and groans, the wind threading through it like a restless spirit. When the gusts rise, it sounds like distant surf rolling on a Cornish beach — a phantom ocean that exists only in the imagination.

And then the moon climbs.
An 80% waxing gibbous — bright, brooding, and otherworldly. Its light spills across the landscape, silvering the grass and turning the granite boulders into glittering relics, each one flecked with mica that winks like frost under torchlight. The clouds become ghost-ships, drifting through a lunar sea, haloed by a faint, perfect circle of spectral rainbow

Off in the Tamar Valley, fireworks ignite the night — a carnival of colour blooming briefly in the darkness. Their echoes roll across the hills like the distant rumble of battle; scarlet, emerald, and gold flares light up the undersides of the clouds. Even the TV masts at Princetown and Kit Hill join the show, their red beacons pulsing like cosmic heartbeats. Below, the headlights of cars carve through the bends of the Princetown road — glowing orbs on a rollercoaster, swooping and diving through the moorland gloom.

Up close, my world is smaller — intimate, ritualistic. The soft, rhythmic clicking of the camera shutter keeps time with the night. The Primus stove hisses nearby, its blue flame bright and defiant against the chill, heating water that bubbles and steams into the cold air. A mug of tea warms my hands, and Fox’s chocolate cookies — a personal tradition — taste better than any banquet could up here.

Tonight’s quarry is fleeting: Comet Lemmon, shy and sinking lower toward the horizon with each passing night. My weather apps promised me one last hour of clear sky around seven — a narrow window, a final chance.  I’m fervently praying I have my calculations right – the moon should be around 50 degrees plus from the comet position.

And so here I am. Binoculars in hand, dipping in and out of the shelter provided by the raised boot hatch, to scan for Arcturus, my ‘lead in’ star for the night. Equipment has been set up on a grassy bank, tripod kept low to stop it vibrating in the wind. Polar alignment finally done; Polaris proved evasive in the small cloud gaps! The ASI air Mini is up and running, shooting details programmed in. The lens is focused – x10 live view and a bahtinov mask.

And suddenly clear skies to the west – the promised gap! I can’t see the comet due to moonlight, by Sy Safari confirms its rough location. My rig is rotated and tilted to focus on a spot in the sky. A test image of 30”. And magically just like, a faint white streak appears on the green home screen of the ASIair app. Comet Lemmon. Gotcher!

Equipment used tonight

Portability, simplicity and quick set-up time is the order of the night given the conditions and constraints. So, I opted for:

• Astro-modded canon 800D DSLR
• Wide-aperture lens – my Samyang 135mm f/2.0 to let in maximum light.
• Benbo Carbon Fibre Sturdy tripod
• Skywatcher Star Adventurer 2i star tracker (essential) - to track the movement of the sky and prevent star/comet trails in individual shots.
• William Optics equatorial wedge
• ASIair Mini – for plate solving the sky ahead of me
• Intervalometer - to avoid camera shake (although I ended up using the ASIair Mini platform in the end)
• Celestron Lithium Battery Power Tank
• Two power banks – to power the dew bands, should they be needed
• Star chart app – I use Sky Safari Pro to accurately locate the comet. 

Camera Settings

Shooting in Manual Mode and RAW file format for maximum control in post-processing, my other settings for this session were:

• Aperture: Set to its widest possible setting (f/2.8), as I find it protects me from slight coma issues at f/2.
• (ISO: Did some test shots to look at histogram and settled on ISO 800 due to the moonlight.)
• Shutter Speed: Always a balance to be had between capturing detail without blurring comet nucleus. I opted for 15” images; hoping that the star tracker will help keep the background stars as pinpoints.
• Focus: Manually focused on a bright star (Vega) using camera's Live View mode and zoom function to get a sharp focus, then carefully panned back to the comet's location. 
• Calibration Frames – depending on conditions, I’ll aim to take thirty or so "dark frames" immediately after my main images, using the exact same settings but with the lens cap on. Followed up by thirty Bias and thirty flat frames.

The end of the night’s story

For the first hour, Comet Lemmon hides — stubbornly veiled behind an unyielding wall of low cloud. I wait, sipping tea, feeling the night settle deeper around me. Then, almost miraculously, the curtain lifts. The comet appears — faint, ethereal, a traveller from the deep — and for twenty precious minutes the sky opens like a gift. It’s a race now, a dance against time and weather. The wind tugs at my jacket, the shutter ticks its steady rhythm, and above it all, Comet Lemmon burns softly in the heavens — a tiny messenger from the edges of the solar system, whispering across the void. I’m genuinely elated!

Settings on the night - Within the gap in the clouds, I managed to obtain 60 x 15” at ISO 800 f/2.8 along with thirty frames each for darks, biases and flat calibration frames. Whilst the camera was busy, I took the opportunity to record the precise dec and RA position co-ordinates – these will be needed for photometric colour calibration in SIRIL over the next couple of days. Throughout the shoot, I checked framing on each image collected.

Should I have used a light pollution filter of some form to combat the moonlight?

I debated all afternoon whether to use my Optolong L Pro clip in filter tonight. Marketed for use with comets in light polluted areas, I was very much in two minds. On the one hand, it’s great at supressing artificial light such as sodium/mercury vapour, sky glow etc. it might well improve the contrast between the comet and stars and the bright sky background.

On the other hand, the filter could reduce signal strength and introduce artifacts like halos or colour cast. In addition, the moon is a strong broadband light source which the filter isn’t really designed to suppress. So, the background may well just remain bright! There is a chance I might also wash out the comet tail details.

Given I was in a dark sky area with very little artificial urban light pollution and was aiming to use shorter exposures for later stacking, and throw in the use of a fast prime lens and the fact that the moon was far to one side of my image framing, I decided NOT to use the filter.

What would you have done in these circumstances?  Have you had success shooting a comet image? What did you do differently to me and why? Share your thoughts and tips in the comment box below so that we can continue to learn together.

As always, I hope you have found this imaging post useful. Good luck in yours, stay safe, have fun and clear skies to you all.

Steve 

So here we are - three rough and ready initial edits of the images - quickly stacked in SIRIL and quick edits in Affinity Photo.  I will spend some time on this later in the week and will do another post about my work flow. 

Want to learn more on how to shoot a comet? https://undersouthwestskies.blogspot.com/2025/10/a-beginners-guide-to-photographing.html

Want to see what my work-flow for stacking this image was in deep sky stacker? Then visit: https://undersouthwestskies.blogspot.com/2025/11/beginner-tutorial-how-to-stack-comet.html

Equipment review: - The William Optics Zenithstar 61ii small refractor scope

 New to this blog, then welcome, and after reading this post why not stop off here and find out more https://undersouthwestskies.blogspot.com/2025/01/welcome-to-my-new-astronomyastrophotogr.html

In today's blog, a 10 minute read, I, 

• review my Zenithstar 61ii refractor scope
• summarise its main features
• identify its advantages
• examine its disadvantages
• discuss who this scope is for 

Equipment: The Zenithstar 61ii small refractor by William Optics

I have owned this small refractor for just over a year and a half now and I thought it was time to review it. If you are considering a ‘beginner scope’ as part of a wide-field imaging set-up, then I hope the following observations will help you weigh up its pro’s and con’s when comparing it against other scopes you may be considering.  

 

My Zenithstar 61ii teamed up with an RVO 32mm Guidescope and the ASIair 120mm mini guide cam.

The mount is the skywatcher EQM-35-PRO; the camera an astro-modded Canon 800D.

Power to the mount and ASIair is supplied by the Celestron Lithium Pro power tank. 

What I like and have found good about the ZenithStar 61 II

1.      Features, Compactness & Portability

a.      Dimensions

                                                  i.      61 mm aperture and a focal length of 360 mm (f/5.9)

                                                ii.      Short 24 cm tube length, (around 315 mm with dew shield extended), 14cm height, (from bottom of mounting plate to top of ‘cat Series’ saddle handle) and 8.5 cm width

My Zenithstar 61ii wide-field rig

b.     Features

                                                  i.      The mounting rings have a ‘Cat Series’ saddle handle bar attached to the top of it which provides a Vixen-style mounting saddle for attaching things like a guidescope.

                                                ii.       The tension-adjustable, dual-speed rack and pinion focuser givers very smooth movement through its 75mm drawtube range and the focuser accepts 1.25- and 2-inch barrels, secured with compression rings

                                              iii.      A micro-focus knob with 1/10th speed adjustment for fine-focusing is so precise and a joy to use and the drawtube is ruled for repeat focus positioning.

                                               iv.      Built in Bahtinov mask which is part of the pull off cap – the lid unscrews to reveal the mask

                                                v.      Pull out dew shield extension which I put a dew band heater around

                                               vi.      I have a ‘love-hate relationship with the thermometer. Useful to monitor temperature for variations that may affect focus; morale sapping when its below freezing!

                                            vii.      Decent mounting dovetail bar

                                           viii.      Optional field flatteners – costing extra but worth the investment – I have the FLAT 61A

Bahtinov mask in-built to the scope cap

Note the rack/pinion control focuser, the dovetail on the clamp rings to hold the guidescope

The field flattener with M48 bayonet/thread adapter just visible in the camera

Also not the scale on the draw tube to help with back spacing. 

My ZS 61ii is really manageable and travel-friendly for astrophotography.  I’ve carried mine in a rucksack along with my star tracker and DSLR. In fact, it’s perfectly teamed with my Skywatcher Star Adventurer 2i tracker (although it did need an extra counterweight) and a perfect fit for my larger EQM-35-PRO mount. Portability – full marks!  I carry some eyepieces with me and a diagonal, so this scope is both my visual and astrophotography one on trips. I leave the field flattener permanently attached, along with the DSLR, so I rarely bother with using this scale.  By the way, I attach my DSLR to the flattener via a M48 screw/bayonet adapter.

 

Out in the field with my Zenithstar 61ii rig

2.      Good optics for its class

An air-spaced doublet with FPL-53 glass (a well-regarded glass type for apochromatic doublets). Various reviews in astronomy magazines such as BBC Sky At Night, report good colour correction. That review said “stars in the middle of the field ‘appeared sharp and bright’ and colour fringing was minimal for the Moon/planet tests”.  So, if you pair it with a camera suited to wide field, you can get pretty decent results without super heavy/expensive gear. Certainly, it works very well with my Canon 800D DSLR. It has an image circle ~ 45mm and I teamed it with a field flattener (FLAT61A) which has improved edge performance.

 

3.      Dedicated astrophotography intent & accessories

a.      Although it doesn’t come with them, I purchased optional dovetail saddles to mount on it – to hold a red dot finder and also my ASIasir mini. My son-in-law also 3 D printed a couple of spare saddles as well for me.

b.      If you want to do wide-field nebulae or star fields, the 360 mm focal length gives you a generous field of view. Stronger user feedback on forums shows people were using the ZS61 II with success for wide-field targets, guided setups, even narrowband imaging. I have used it for taking photos of the moon with some success – some good shots of lunar craters; its small aperture doesn’t collect a lot of blinding lunar light. I’ve used it with success on M45 Pleiades, M42 Orion Nebula, M33 Triangulum Galaxy, M31 Andromeda Galaxy just to name a few examples. Use telescopius.com and enter the scope, your camera and reducer details into the telescope simulator tool and then look at various targets to get an idea of what you will visualise/image with it.

c.      A quick search of Astrobin shows many fantastic images taken by astrophotographers of deep space objects. It has a proven track record. Because it’s used by many hobbyists, there’s a fair amount of discussion about spacing, flatteners, mounts etc on the popular astrophotography forums. That means useful advice is available for users.

 

Above: close up of the focuser, dovetail base bar, rings and handle

Below: side view showing guidescope (RVO 32mm F/4) and guidecam(ASIair 120mm mini); also ASIair mini on saddle screwed to optical tube assembly. Also visible is thermometer

4.      Looks quality built
What I am really impressed with is the build quality. Nothing feels compromised on it. It is a precision piece of engineering, well designed and well built. Truly functional and fit for its purpose. It just works straight off without any fiddling about.

Proof - it can be successfully used on a skywatcher star adventurer 2i tracker

So, lets turn to the dark side for a moment.

 What are the limitations (and what to watch out for)

Small aperture & moderate light-gathering

• With only 61 mm of aperture, you’re inherently limited in how much light can be captured compared with larger scopes (e.g., 100-120mm, 150mm or more). I struggle to do justice to faint deep-sky targets sometimes; an issue probably exacerbated by modest mounts and light-polluted skies). Let’s be realistic, it is optimized for wide-field, moderately bright targets (nebulae, clusters) more than very faint galaxies or ultra-deep exposures. I knew that when I purchased it

Edge performance / need for flattener

• While the optics in the centre are strong, without the optional field flattener, I read reviews and forum threads where people noted vignetting and distortion towards the edge of frame. On a full-frame camera set-up – you will need the optional field flattener if you want sharp stars right across the frame. I got it even for my APS-C crop camera. It did take a little bit of working out with my camera on ensuring that the spacing and back-focus spacing was correct but William Optics supplied a helpful leaflet explaining how to do this.

Mount & guiding requirements

• I’ll be frank here. On my tracker, the most I could get without guiding as an exposure was around 60” using this scope. 90” on a very good night. Anything over that and I was getting trailing. Polar alignment has to be extraordinarily accurate; your tripod very stable and you’re balancing really good! Team it with ASIair autoguiding and its awesome.

Potential for awkward positioning 

• In some setups, the focuser can be positioned awkwardly due to the dovetail bracket, requiring the telescope to be mounted upside down. I find it tricky when mounting it to my EQM-35-Pro mount – the focuser knob only just clears the mount side clamp by around a millimetre or so. You can see how close the focuser is to the ground in this image

when in my EQM-35-PRO mount, the mount clamp wall comes up to within a millimetre of the base of the silver focuser knob. Its a tight fit 

Less suitable for high magnification / planets / small targets

• With 360mm focal length and f/5.9, this isn’t designed for high magnification work (planets, lunar close‐ups) or very small targets requiring high resolution. So, not so good for planetary imaging or the really small deep sky objects.

Cost relative to aperture

• You pay for build quality and brand (William Optics). You could get larger apertures for similar money from other brands (though with different trade-offs). I often wonder if some William Optics products are overpriced – so when thinking about the Zenithstar – is the premium worth it for a small refractor or would it be better to get something else a little larger? I wouldn’t by the way always say that about all William Optics products – the RedCat series for example, are as far as I can ascertain, always very highly regarded as value for money by many astrophotographers.

Bottom line then, who this scope is really good for

• Someone like me, who wants a lightweight wide-field imaging setup (star tracker/ small mount) and wants decent results without hauling big gear. This is me – portability and compactness are key as I often take my astrophotography rigs with me on my travels in a small motorhome where payload considerations are at the forefront of my mind; and I walk out to some wild dark sky sites, having to carry all the gear in a big backpack.

• Someone, like me, who is happy to learn the craft and skills by focusing on nebulae, star-fields, Milky Way, large scale deep-sky rather than tiny galaxies or extremely faint fuzzies. In saying that I have managed to image several galaxies with some success.

• Someone who appreciates built‐in features like dual‐speed focuser, Bahtinov mask cap, good build quality, and is willing to spend a little extra (for flattener) for better performance.

 

Who should probably look elsewhere (or treat this as a secondary tool)

• If your goal is serious deep‐sky faint object work, very long subs, or large sensor full-frame with perfect corner stars and minimal aberrations without flattener. In that case, a larger aperture refractor/triplet or a dedicated astrograph might be more effective.

• If you plan planetary/high magnification work (Moon/planets) as your main focus — you’d benefit from a longer focal length or higher resolution optics.

• If budget is tight and you’re prioritizing aperture per £, you might consider alternatives that give you more light grabbing for same price (but maybe trade off portability/build/brand).

• If you prefer “plug and play” and don’t want to worry about flatteners, back-focus spacing, or corner distortion— then a bigger system might still require those, but the relative impact could be less.

 

Despite the rising moon, I take my chances when I get clear skies - here in the Sennen area of Cornwall 

The William Optics ZenithStar 61 II is a fascinating little wide-field refractor for astrophotography. I value its excellent portability, good optics for its size, and its wide field-of-view - perfect for nebulae and star clusters. It is a great ‘grab and go’ scope which I can set it up within minutes; for both visual and wide-field viewing and astrophotography. Compact and light is why it accompanies me on all my motorhome trips; it weighs 2.15kg. Just add a camera and you have a quality, easy-access imaging setup. It’s supplied with a padded carry-case, which is large enough to accommodate optional extras, such as the recommended field-flattener, but not a guide scope – which is a minor irritation.

Useful resources:

William Optics manual pages for zenithstar at https://support.williamoptics.com/products/zenithstar-61-ii

The videos below are ones that I found useful. I take no responsibility for their associated links etc. 

review - An almost 'end of year one' blog review

 If you are new to this blog and want to learn more about it, then firstly, welcome, and secondly why not start here at https://undersouthwestskies.blogspot.com/2025/01/welcome-to-my-new-astronomyastrophotogr.html

A 'cheating' composite photo

A separate foreground shot of our motorhome Bryony, recently out at Weymouth

A se[arate 'stacked' sky shot of  the Orion area which has been cropped and then blended with the original foreground shot. 

I just wanted you to see where I am slowly progressing to on my astrophotography/astronomy learning journey. 

An almost one-year review of the blog

I’ve conducted a brief review of my blog based on feedback from people who have visited it, an analysis by Chat GPT (I just wanted to try it out, having never used it before) and the patient ‘critical friend’ thinking that always comes from my wife.

I’ll just focus on the areas I want to improve over the forthcoming year for now, but if you want to read about my original aims for this blog then you can find them here at https://undersouthwestskies.blogspot.com/2025/01/what-is-aim-and-purpose-of-my-new.html

Some possible blog improvement areas for 2026 could be: 

1.      Posts about acquisition of data and use of equipment are sound but I need to improve the clarity, depth, and readability of ‘post-editing’ tutorials. I also need to include more ‘before/after’ comparison images, explaining step-by-step what I did to get the improvements

2.      Whilst some of my posts are more narrative and less structured, which is fine, I need to include more consistent elements to improve usability for myself and readers e.g. ‘summary of key points’, ‘what I’d do differently next time reviews’, ‘bonus tips’

3.      I need to better categorise posts through their titles to help me and others find their way around the blog e.g. ‘Beginner guides to ….’ ‘Gear reviews’ ‘Image capture’ etc

4.      Increasing interactive features like comment prompts, Q+A posts, regular reader submission pages, ‘How did your results go?’ etc to build up more of a community feel and participation rate

5.      Improve the SEO, discoverability and broader reach of the blog. Use more long-tail keywords (uur??) and more tags/categories. An old IT friend of mine said “make your older posts easier to find and navigate”. And a very social media savvy younger friend of mine, well she said “more visual thumbnails, more summaries for sharing on social media, get an Instagram page”. Gulp!

6.      Two young, world travelling, former students of mine suggested some more varied content could broaden blog interest e.g. “‘Astrophoto travel stories’, ‘Visiting dark-sky sites’” (they were in La Palma when they suggested this one!); “‘interview some fellow local astronomers and astrophotographers you know’” (another of their suggestions). ‘Challenges and setbacks’, ‘Quick tips’. Lots to think about going forward.  

7.      The whole ethos of the blog is based on ‘going on a learning journey of self-improvement’ in astrophotography and astronomy, so is there a way I can provide a visual ‘roadmap’ of the site which gets regularly updated e.g. “If you’re just starting, do X, then Y after you’ve mastered A, then move to B”. Would this move the blog from being more of a journal to more of a community resource?

This was my very first effort at imaging M42

Taken from Cathagena in southern Spain in 2023

So, almost a year in, lots to ponder. I think the blog is beginning to get a strong and authentic feel; one that shares a learning journey in a relatable way backed up by practical details, an honest approach and even, perhaps, a niche focus on ‘beginners’. We will see how it goes forward in 2026. I, for one, will still be out there trying to capture images of our amazing cosmos. I will still be grappling with developing some reasonable post-editing skills for both milky way landscapes and deep space objects. I’ll still be trying to learn and remember all the constellations. I’ll still be trying to learn the basics about the cosmos.

As always, drop me a ‘hello’, introduce yourself, tell us about your own learning journey in astronomy and/or astrophotography. Share an image you are pleased with. Pose some questions.

And, stay safe out there, clear skies and have enormous fun

Steve

An alternative view of the Rosette Nebula

Translated, that means "I did something wrong in post processing but I haven't yet worked out what or how"

Taken in 2023

Beginner's guide to photographing comets

 First visit to this astronomy/astrophotography blog? Well, firstly a warm welcome to you and thanks for stopping by. After reading this post, if you want to find out more about me and this blog, why not visit my introductory page at https://undersouthwestskies.blogspot.com/2025/01/welcome-to-my-new-astronomyastrophotogr.html  You can also browse other posts by using the search bar or the blog post list on the right hand side and I'd really like to hear from you via the comment boxes. Drop me a tip, an observation or a question. Take care and clear skies to you.  Steve 

In today's blog, a 10-minute read, I 

• describe Comet Lemmon
• outline some beginner's tips for capturing this or another comet image
• suggest a way to post-edit your image of a comet

Detected first on 3^rd January 2025 by the Mount Lemmon Survey in Arizona, pre-discovery images from the Pan-STARRS survey date back to November 2024. Initially thought an asteroid, follow up observations revealed a condensed coma and faint tail. A long-period comet! With perihelion to the sun on 8^th November 2025, its inbound orbit period is around 1,350 years. And it comes from far out in the solar system, probably the outer Oort cloud. So, this is a relatively rare visit to the inner solar system. 

Like other comets, Lemmon has a s small rocky or icy body nucleus and a coma where solar heating has caused ice to sublimate, releasing dust and gases to form the fuzzy cloud around the nucleus. Its tail is broadly curved, of diffused ionised gas, bluish-green in appearance. As the comet gets closer to the sun, sublimation will increase, releasing more material and enhancing they coma and tail. Solar wind and radiation pressure, as it approaches the sun, will continue to ensure that its tail points away from the sun.

Lemmon, with its eccentric and retrograde orbit as it approaches the sun, is probably an early relic from the formation of the solar system and so it gives astronomers a chance to study material relatively unaltered since then. Like many of our visiting comets remaining unchanged as they arrive in our area of space, our sun heats them causing their icy nuclei to release gas and dust on tails and comas that reveal their composition. Studying this material allows us to learn what the early solar system was made of and how planets such as ours may have formed; delivering water and organic materials, the building blocks of life.  Lemmon carries fresh samples of this primordial material – its chemistry and dynamics is of critical interest.

I have only photographed one comet so far and I found it one of the most fun bits of astrophotography I have done so far on my learning journey. The comet changed its appearance every night I went after it and you can read more details here at this previous post:  https://undersouthwestskies.blogspot.com/2025/01/chasing-comet-c2023-tsuchinstan-atlas.html

The positives - I located the comet and managed to image it. The 'future learning'? Getting my editing skills better developed, particularly on white balance!! 😆

I used Sequator to stack several images. 

Clearly at the time I hadn't then discovered 'freeze' ground' and also 'stack for comet' options!

I'm aiming to do much better on Comet Lemmon - if the cloud ever actually clears away long enough in the south west 😱 

Anyway, moving on - what are my ‘beginner’s’ tips for capturing this latest cosmic visitor, if you haven't caught one before?

1.      21^st – 26^th October, when it makes its closest approach to earth and is at its brightest. It is also when there is no or only a faint presence of a new moon

2.      In the northern hemisphere, it will appear in the NW sky after sunset (30 – 90 minutes), once twilight has faded.

3.      Find a clear unobstructed horizon in a dark sky site away from light pollution and be aware that as the night progresses this comet will appear lower and lower in the sky;

4.      Look for the constellation Boötes and its bright star Arcturus as lead in points to its location.

5.      Because it is low on the horizon, try to include some foreground elements such as trees, hills, silhouettes to add context and scale

6.      Its tail will probably point roughly away from the sunset west direction and somewhat downward

7.      A wide to moderate focal length e.g. 24 – 70mm on a full frame camera, or a longer lens/telescope if you want detail in the coma and tail; try ISO 800 – 1600, aperture F/2.8 – F/4 on a fast lens. Exposures 10 – 30” depending on your focal length and whether your mount tracks or not. Shoot in RAW

8.      You could use a star tracker with a 200 – 500mm lens or small refractor for greater tail structure, again ISO 800 – 1600, 20 – 60” and aperture F/4 – F/5; if you are not using a tracker – take multiple 1 – 5” shots and stack them later in software but align on the comet rather than the stars or do both and merge, to keep the nucleus sharp. 

 

Because of its low elevation, there may be atmospheric issues to deal with:

1.      Pick nights with good transparency, if possible, to combat reduced contrast and also haze issues

2.      Try for a clear horizon line under such circumstances; avoid shooting towards sunset glow

3.      Mitigate atmospheric blur and tail motion by taking many short exposures

4.      Use a light pollution filter if you are under lights

 Composition and framing

My Achilles heel in astrophotography and I do try hard to improve it. For comets, which are highly dynamic subjects, composition matters; go for foreground elements such as trees and mountains in wide angled shots. Comets tails always point away from the sun, so that helps in framing the subject. Try to align the comet’s tail diagonally through the image for a dramatic composition. Look for potential juxtapositions – a bright star, a star cluster, an element of the milky way.

How do you do the post processing of your comet image?

1.      In the past I have combined stacks – one aligned on the stars and one aligned on the comet – blending them afterwards in something like deepskystacker or SIRIL - masking carefully to retain both sharp stars and a crisp comet nucleus.

          Combine the two images by blending them together in photoshop or affinity photo

2.      Levels and curves adjustments should aim to extract tail detail without blowing out the coma; use noise reduction but preserve the faint structure in the tail

3.      Colour balance, try to preserve the greenish hues

4.      Crop and sharpen GENTLY to bring out structure without over processing to get artefacts.

What about some beginner tips for shooting comets generally?

1.      Do your research using sources like Sky and Telescope, Sky at Night, etc to learn where and when the comet will appear.  More often than not, best times are when the comet is far from the sun in the sky – so typically visible before dawn or after dusk and when the moon is absent or below the horizon. Choose nights when it is higher in altitude above the horizon to avoid atmospheric haze and light pollution. Stellarium and Sky Safari apps will help you visualise where the comet will appear relative to your horizon, and constellations above.

2.      I have already mention equipment choices above but to build on that:

a.      A DSLR or mirrorless camera that shoots in RAW format. An astro-camera will get deep detail but isn’t essential.

b.      Lens or telescope? Tough question! Wide angle (14 – 50mm) will capture the comet in context with the landscape or milky way. Telephoto or small refractors (100 – 300mm etc – will reveal coma structure and tail detail

c.       A tracking mount such as a skywatcher star adventurer 2i (other brands are available) will allow you to go beyond the limit of shorter exposure times

d.      Tripod and intervalometer enable stability and no vibrations.

e.      Camera settings – how long is a piece of string? If I were doing a TRACKED image then I’d probably go somewhere with ISO 800 – 1600; F/2.8 to F/4 for wide angle lenses and F/4 to F/6 for telephotos; exposures 20 – 60” if tracked and 2 – 10 “if not.  White balance daylight or 4000K

f.        Multiple frames rather than one long exposure are better, it improves signal-to-noise ratio and allows stacking later.

g.       And always shooting in RAW

 

Photographing comets is a unique challenge that combines astrophotography, artistry and timing. Prepare well, bring the right equipment, master your post editing workflow and remember, you are capturing a rare celestial event and ancient cosmic visitor.