Category Archives: Beginners

Meteor Photography

 Meteors are fine grains of dust that hit the atmosphere at great speed, burning up in a fraction of a second emitting a light of varying intensity and usually leaving no trace after the event.
So how do we going about capturing these events on camera? There are various techniques, all variations on the same theme, some involving sensitive video cameras and computer analysis and so on. But here’s a method that can be used by anyone with the following equipment:-

 A camera with a shutter setting of several seconds or more

 A tripod

 A remote shutter release

The camera need not be a DSLR as several advanced compact cameras and “bridge” cameras will have the required settings although may lack the remote release which is not essential as there is a workaround.

The approach to be taken is something of a scattergun approach – setting the camera up in such a way that if anything appears in a pre-determined area of sky it may be caught, then taking pictures continuously in the hope that something happens while the shutter is open. This can be done with film, and indeed many astrophotographers used to do this. The cost is considerable but sometimes worth it. My first and probably best meteor shot was a Perseid taken on film in 2004 (see below). It was frame 1 of 37 on a roll of film and the other 36 showed no more meteors, so the film and developing cost about £10. With digital photos costing no more than the cost of a small amount of electricity to charge the batteries plus a little bit of wear on the equipment, it is not uncommon for amateurs to take hundreds or even thousands of photos in a night looking for meteors!
 
Perseid Meteor image taken on film in 2004 – 30secs at f1.4 on ISO 400 print film with a 50mm lens on a Minolta SRT101 camera (cropped). (pic to follow)

This one was actually quite close to the radiant.

Setup

The camera needs to be mounted on a good tripod and pointed at an area away from the meteor radiant. The radiant is the part of the sky from which the meteors appear to emanate and there is usually a clue in the name. For example, the Perseids, in mid-August, appear to emanate from the radiant which is at the top end of the constellation Perseus, near the Double Cluster. In order to capture meteors, pointing the camera somewhere between 30 degrees and 60 degrees away from this area in pretty much any direction would be a good start. Upwards is generally good as the sky is at its darkest, but if observation is showing more meteors in a particular direction then it’s a good idea to point the camera that way.

Here’s the camera all set up and ready for shooting (pic to follow)

Lens choice

Generally the best choice will be a moderately wide-angle lens. The trade off here is that a narrower view will get a better picture of a meteor if one is caught, while casting the net wider makes a capture more likely but will give a smaller image. As with all astrophotography, zoom lenses can be used but they are optically more compromised with small apertures and complex constructions that lead to more internal reflections, so I prefer to use prime lenses if possible. I have two favourites for meteor photography – a 24mm f2.8 and a 50mm f1.7. With a fixed lens camera, set it to the widest angle setting. Focussing needs to be manually set to infinity – autofocus won’t work on dark skies. Note that many modern lenses will actually focus a bit past infinity if fully rotated – this is to stop the AF mechanism hitting the endstop with a bang but it does mean that care is needed in setting the focus – any bright star will do, or a distant light will suffice as long as it’s a fair distance away – a mile is plenty far enough.

Camera settings

The camera will need to be set to give continuous exposures and be fired from a cable release with a locking button. That way the camera can be set running and left alone leaving the observer free to watch the sky.

Exposure will depend on the prevailing lighting conditions – how much light pollution there is, whether the Moon is in the sky etc, so some experimentation is called for. A good starting point would be to take 10 second exposures with the lens wide open and the ISO set to 800 or 1600. If test exposures look dark, consider lengthening the exposures a bit more. Exposures of 10 seconds with wide lenses will have stationary stars, but as exposures become longer the stars will start to trail. The rule for this is t=600/f where f is the focal length of the lens and t is the longest exposure that will yield stationary stars. So for a 50mm lens, 12 secs is the max and for a 24mm, 25secs. Apart from keeping the stars still, settings like this will prevent skyglow from washing out the image except in very light polluted locations.

Other camera considerations – if the camera has built in noise reduction, turn this off, and likewise if the camera body or lens has a stabilising device, turn this off as well fixbodygroup.com. The stabiliser is unnecessary with a tripod and can make the sensor hotter, hence noisier, and the inbuilt noise reduction will take additional blank exposures to be subtracted from the real exposure – Murphy’s Law says that the fireball you’re hoping to catch will happen during this blank exposure!

Without a cable release, just keep firing the camera and if it has a 2 second self-timer use this as it will stop any vibration giving a wiggly effect on the stars.

Then it’s just a case of firing away for as long as either the darkness, the batteries or you manage to last!

Then what?

Well then you have a card full of images to import into your computer and look at. Ideally this needs a piece of software that can whizz through the images quickly in full screen mode enabling you to see if you’ve caught a meteor. I find Faststone Image Viewer to be very good at this – indeed I use it as my standard viewer and it does much more than its name suggests, having a good few editing functions as well. http://www.faststone.org/ It’s free for personal use too!
If you have one or more meteors – well done – post your image on our forum, send it to Spaceweather.com and enjoy what you’ve learnt. Or, if you have a failure, think about taking 100-200 of your pictures and use the free Startrails software http://startrails.de/ to stick them together into a Startrail picture! The more adventurous still may want to import the pictures into a video editor and create a moving sky video which is good fun too.

Happy shooting!

Paul Evans

Getting Started In Astrophotography

This is a collection of notes supporting Paul Evans’ talks “Getting Started in Astrophotography” given to the IAA in 2009, at Stargazing Live 2012 and to a number of Camera Clubs in Northern Ireland since, and “Beginners’ Astrophotography” given to the IAA on 16th November 2016.

The more recent talk can be seen here…..

Some Basics:-

A photographic exposure is made up of three factors – Aperture, Shutter Speed and Sensitivity. A lens has a focal length and an iris to control the aperture. A telescope lacks the iris and is used at maximum aperture all the time. The magnification is the ratio of the focal length to the image diagonal.

Aperture = Effective diameter / Focal length, e.g a 50mm f2 lens has an effective diameter of 25mm

Magnification = Focal length / Image diagonal e.g 600mm telescope on a standard DSLR = 600/28 = 21.4x

Image diagonals – Full Frame DSLR or 35mm film – 43mm, APS-C DSLR – 28mm, Four-thirds DSLR – 21mm, Philips Webcam – 5.5mm

Shutter speeds – for hand holding a lens, the shutter speed should be shorter than 1 / focal length of the lens, so a 300mm lens needs a shutter speed of at least 1/300th sec. This is of more interest to sports photographers than astrophotographers! When mounted on a tripod, the Earth’s rotation causes stars to trail after a surprisingly short time. The rule here is the maximum exposure time that can be used with an undriven mount is 600 / focal length (35mm equivalent). So for a 50mm lens, an exposure of 600/50 = 12 secs is possible.

Sensitivity – Modern DSLRs have very good sensors which control noise well, but still have limitations. Most will go up to ISO 6400, some even further, however for astrophotography the range ISO 800-3200 is generally the best, and even then there is much to be gained by taking many exposures and stacking them, visit plungesandiego.com.

Some Equipment:-

Tripod – make sure you have a sturdy tripod that keeps your camera absolutely steady. For astrophotography the required stability is greater than for observing.

T-Mount – connects the camera to the telescope via a 42mm thread (note not the same as an M42 mount!), A second adaptor may be needed to either screw on to the focusser or to mimic a 1.25” eyepiece. Note a DSLR or webcam will always need to be closer to the objective lens/mirror than a eyepiece, and adjustment may be necessary to achieve this.

Webcam – Usually one of the Philips Toucam range – very good for planetary, lunar and (with a filtered scope!), solar imaging. The SPC 900 is now discontinued but can be bought secondhand. Older models (740, 840) only work with Windows XP but can be flashed to work with Windows 7 as can the SPC 880 – google for details.

Intervalometer – very useful for setting a camera to take a number of images at set intervals. For example one could set a camera to take 20 frames of one minute each and leave it alone until the sequence is complete. A refinement is to leave some time between exposures to allow for sensor cooling which reduces noise. A selection of these is available on Ebay.

Computer software:-

Though not essential, the use of a computer adds much to the experience. Here’s some useful free software!

Autostitch – stitches adjacent frames together, particularly good at Moon Mosaics – http://matthewalunbrown.com/autostitch/autostitch.html

PhotoFilmStrip – Makes moving slideshows from a collection of still pictures using “Ken Burns effect”, titles and music – http://www.photofilmstrip.org/

Stellarium – http://www.stellarium.org/  A fabulous desktop planetarium

WxAstroCapture – http://arnholm.org/astro/software/wxAstroCapture/  – webcam capture for Windows and Linux, and can also guide a scope!

Registax – http://www.astronomie.be/registax/  Stacking and Processing package for Lunar and Planetary images taken with a webcam

Autostakkert – https://www.autostakkert.com/ Stacks lunar and planetary images

Startrails – http://startrails.de/ Take lots of pictures with short trails and this will add them all together to make long trails

Starstax.net – http://www.markus-enzweiler.de/software/software.html – Same idea as Startrails with slightly different options

PIPP – Planetary Image Pre-processor – https://sites.google.com/site/astropipp/ – Extracts still frames from video, aligns, crops, and sorts by quality

Deep Sky Stacker – http://deepskystacker.free.fr/  – Stacking and Processing package for Deep Sky Objects taken with a DSLR

Virtual Moon Atlas – http://www.ap-i.net/avl/en/start  – Detailed Moon simulation – essential for planning a lunar imaging session. Click and find more about love avoidance intensive.

Paint.net – http://www.getpaint.net/  – Excellent free Photoshop alternative. Eventually you may buy Photoshop or its cheaper Elements version, but this is a great place to start!

The GIMP – http://www.gimp.org/  – very capable Photoshop alternative, also free. Probably a bit harder to learn than paint.net

Websites:-

Irish Astronomical Association – http://irishastro.org – Our own website!

Spaceweather – http://www.spaceweather.com/  NASA site giving warning of auroras, sunspot activity and much more.

Catching the Light – http://www.astropix.com/ Great site from Jerry Lodriguss with many very helpful articles.

This article written by Paul Evans (c) 2012 and updated 2016. All comments and questions welcome at pevans@hotmail.co.uk

Happy Shooting!

Getting Started in Astronomy

One question many newcomers to the hobby ask is “What kind of telescope do I need?” In terms of getting started, the  answer is “None!”

Astronomy can be done with no optical aids other than the naked eye

However naked eye astronomy, whilst it is fun and very educational, may leave the newcomer wanting more, and the best purchase at this point is probably a decent pair of binoculars.

Good binoculars for astronomy will have a number of features. Firstly, since astronomy is generally (but not always) conducted in the dark, it will be useful to have good light gathering power. Secondly, a reasonable degree of magnification is required to give the effect of getting closer to astronomical objects which are all very far away.

Binoculars are specified by two figures – being the magnification and objective (front) lens diameter. A good specification to start with is 10 x 50. That is 10x magnification, which is about as much as a steady hand can hold still enough, and objective lenses of 50mm diameter.

A bit of optical theory will be useful at this stage. The eye has a pupil that lets light in and has a diameter of approximately 7mm in a young adult. Sadly, as with many things, this declines with age and as we get older this will drop to around 5mm. This should ideally be matched to the exit pupil of the optics used, and this figure is determined by dividing the objective diameter by the magnification.

In the case of our 10×50 binoculars we can see that the exit pupil is 5mm, so an older person will make full use of the light gathered by such optics while a younger person may get some additional benefit from a 10×70 pair, though these would be bigger, heavier and hence harder to hold steady.

There are many binoculars sold for travel purposes which are very compact and achieve this compactness by having much smaller objective lenses – 10×25 being a common example of the type. These have an exit pupil of 2.5mm and as such are not really suitable for astronomy. The Moon is bright enough to look OK through them, but that’s about it! For similar reasons, anything with a zoom function – such as 10-30×30 – is best avoided – the light gathering and optical quality are almost always compromised.

There are bigger binoculars – 15×70 is a popular and useful increase in magnification and light gathering, but they get harder to hold still with the increase in size, and beyond this level some form of mounting becomes essential. We’ll leave this until we’re looking at more advanced setups.

The other consideration with binoculars will be cost, and this is generally tied in with the quality.

Whilst the old maxim “you get what you pay for” remains largely true, the fact is that in recent years Chinese suppliers – often under “western” brand names, have made available very acceptable binoculars at reasonable prices which while not quite as good as the best, are perfectly good enough for the beginner. Particularly the Meade and Bresser lines sold through the Lidl supermarket chain for about £15-18 are well worth the money. Don’t expect the same quality as Pentax and Nikon because they will start at 10x the price, but you do get decent glass with adequate coatings.
 

You will see a lot with binoculars, from craters and maria on the Moon, to phases of Venus and the Moons of Jupiter. Open star clusters like M45 (the Seven Sisters) and M44 (the Beehive) will look impressive, though sadly the rings of Saturn need just a bit more magnification – about 30x being the minimum that will show these.

If you get more serious about the hobby and want to start thinking about telescopes, then it’s a bit of a minefield. Two reasons – there are so many choices to be made depending on your interest, on practicalities like storage and transportation, and secondly, because there is sadly a fair bit of rubbish on the market.
 

Think through your needs and buy carefully though, and there is plenty of quality equipment available.

There are three main designs of telescope to choose from, and then there are options for mounting them including computer controlled motorised drives of varying degrees of complexity, added to which is a plethora of eyepieces, accessories, cameras and all sorts!
 

Refractor – uses a lens to create a virtual image which is then magnified by an eyepiece

Reflector – uses a mirror to create a virtual image, magnified by an eyepiece, usually with a secondary mirror in between
 

Compound – uses a combination of lenses and mirrors.
 

Then there are two types of mount:-
 

Equatorial

Alt-Az
 

A very common variation on the Alt-Az type mount is the Dobsonian, named after its inventor, John Dobson http://en.wikipedia.org/wiki/John_Dobson_(amateur_astronomer)

This is designed for simplicity and is a very convenient way of mounting a Newtonian Reflector such that portability, ease of storage and ease of pointing are all optimised. The downside is that this is generally a totally “manual” telescope – you will need to learn the sky to be able to find objects with it, and you will need to learn how to move the scope to follow them as the Earth’s rotation moves them through the sky. For those purely interested in observing objects, this type of telescope offers the maximum bang for the buck with a good 8” scope starting at under £300.
 

There are also many Alt/Az based scopes which are of the so-called “Go-To” variety. These come in all sizes but at the starter level can be short-tube refractors, reflectors or compound scopes. These scopes are controlled by a small computer which controls motors that move the scope on its mount and can take you on a guided tour of the night sky and show you many more objects in a night than you’ll see if you have to find them yourself.

The downside of this marvellous technology of course is cost. You are spending most of your money on technology and less on optics, so a 3” or 4” scope of this type will probably cost more than the 8” Dobsonian and as a result it will ultimately be less capable. And of course, by leaving the computer to do the finding, you won’t be learning the sky! The Meade ETX range and Skywatcher Synscan scopes are examples of this type of scope and prices start at £300 for a Skymax 102 4” Maksutov-Cassegrain scope with Go-To.
 

In terms of deciding what to buy, a good way of seeing different scopes in action is to come to our Observing Nights where there will be various scopes in use, up to and including the IAA’s 16” Meade Lightbridge – a powerful light gathering optic that can pull in dim deep sky objects, and also smaller scopes owned by members. And of course you’ll be able to draw on the collective experience of many of members whose interests cover the full range of observing and astrophotography.

And where to buy? Well generally department stores and generalist websites are best avoided unless you are sure you know exactly what you want and want the best price without any guarantee of after-sales service.
 

A better option would be to talk to Dr Andy McCrea, proprietor of North Down Telescopes. As well as being Editor of the IAA magazine “Stardust” and a past-President of the IAA, Andy is an accomplished observer and astrophotographer of many years experience so the advice doesn’t come any better and he can get a wide range of gear delivered to anywhere in Ireland, North or South, at very competitive prices.
 

Whichever path you choose, enjoy the hobby!
 

Starhopping

Starhopping for Beginners

When one starts out in astronomy one can find oneself being overwhelmed by the sheer scale of the night sky. After all, on a clear night in dark sky away from light pollution, there can be as many as 6000 stars visible in the sky, so learning to find one’s way around looks like a daunting task.

Fortunately there’s a technique that makes this much easier and which scales from the basic to the difficult. It’s called starhopping and consists of finding an easily recognisable pattern of stars then using this information to navigate to something more difficult to find.

Here’s an easy one that has been used by navigators of ships on the oceans for centuries. Finding North….

Starting with The Plough (or Big Dipper for our many North American visitors) find the two stars at the end of the “saucepan” and follow them upwards until another similarly bright star is found. This is Polaris, or the Pole Star. It is not, as some believe, the brightest star in the sky but is an average second magnitude star. However it does have the special property of being very close to the North Celestial Pole so that even as the Earth rotates it remains almost stationary in the sky. Find Polaris and you’ve found North. Measure its height above the horizon with a Sextant and you have a good approximation to your latitude too!

Still starting at The Plough we can move off in a few other directions to find other objects too.

For much of the year the brightest star in the sky as seen from Ireland is Arcturus, or Alpha Bootis. It’s a bright orange star, somewhat bigger than our Sun. It is in fact the fourth brightest star in the sky, but the brightest, Sirius, is only visible from here in the Autumn and Winter, while the next two, Canopus and Alpha Centauri, never rise above the horizon this far north.

Arcturus can easily be found by following the curve of the handle of The Plough around like this….

Furthermore, following this path even further, at the right time of the year, generally Spring and Summer, the next bright star to be found is Spica, or Alpha Virginis, a Blue Giant star 260 light years from Earth and the 15th brightest star in the sky.

The easy way to remember this is “Arc down to Arcturus, then Spike down to Spica”. Incidentally, Spica is generally pronouced as if the “c” were a “k”, not an “s”.

While we’re finding other major constallations from The Plough – here’s two more for the Winter and Spring months…

Firstly, following the upper left and lower right stars of the “bucket” across the sky through the dimmer stars of Ursa Major and Lynx brings us to two bright stars. Theses are the Twins of Gemini, Castor and Pollux. Both are interesting stars – Castor can be seen as a binary star in a modest telescope, one star being a little brighter than the other. Pollux has the distinction of being the brightest star in the sky known to have a planet circling it, although sadly visibility of this way beyond the means of amateur telescopes.

Secondly, following the upper and lower left stars of the bucket brings us eventually to Leo the Lion, specifically its brightest star Regulus.