Matt in the Moon

27 April 2014

Total Lunar Eclipse April 2014

After a string of cloudy Melbourne Autumn nights, the sky cleared just in time for me to capture the Lunar Eclipse on April 15th, 2014. A time-lapse video appears below.

Time-lapse video of the total lunar eclipse on April 15th, 2014.

For this one, I used my RC8 telescope with a Canon 700d and put together a time lapse video. Each exposure was taken 20 seconds apart, although I did miss some while mucking around with the exposure settings. The focal length of the RC8 is such that the moon only just fit within the field of view. I hadn't the opportunity to align my mount properly (set it up during the afternoon - the eclipse began before it was dark), so the moon drifted slightly out of the field of view at times.

Other things that made it into some of the frames - power lines across from my deck (the dangers of urban astrophotography) and a small aircraft flew across during one of the exposures.

Some Details:

RC8 telescope has a focal length of 1635mm and aperture of 200mm. Mounted on an EQ mount, although not polar aligned.
2 second exposures at ISO 400 every 20 seconds (or thereabouts). Altered the exposure settings for the last several frames. Probably shouldn't have.
Canon 700d has an APSC sensor and a very handy swivel screen.
I haven't altered the colours of the images - so the red moon isn't artificially enhanced unlike, some of the lunar eclipse images that I've seen on the online.
I eventually aligned the output images using Photoshop (crashed far too much, so I had to align small batches of images then manually align the batches - a real pain). The video was generated using Final Cut Pro X.

There's another total lunar eclipse in October 2014. Next time round I'll hopefully have a focal reducer in order to have the moon a bit smaller in the field of view, to avoid it getting clipped when drifting. I'll also polar align the mount before the eclipse.

It also looked pretty amazing, though an 80mm refractor telescope that I had piggy-backed to the RC8. I recommend checking it with binoculars next time round if you don't have a telescope!

The 'blood moon' - total lunar eclipse April 2014.

2 January 2014

Astronomy - Planets

Planets - A Quick Summary

I'll start with a summary relating to observing and imaging planets. Specifically Jupiter and Saturn, which I find the most interesting.

Planets are very small in the sky.
Saturn and Jupiter provide the best views as they are large, unique, although far away.
Mars looks like a red/orange ball.
Venus can be seen to have phases, just as with the moon. It is otherwise featureless.
The other planets won't show any details except for colour.

What do I need to view planets?

Using Saturn and Jupiter as an example:

Magnification is important to provide a larger view.

Any telescope where the focal length, eyepiece, and other lenses such as barlows provide suitable magnification. Around 120x magnification is the minimum you'd want. The photo of Saturn above was produced at about 291x magnification, although through an eyepiece it will look several times smaller (the camera can produce a large image due to the sensor resolution).

I have a 400mm refractor and with an 11mm eyepiece and 3x barlow (about 120x magnification):

Will show Saturn, with bulges of the rings just visible (this is small).
Jupiter will be visible as a small ball, possibly with a storm band visible. Four or five moons are typically visible as bright dots.
You definitely know you're looking at these two planets rather than stars.

I have a 1500mm Newtonian telescope and with a 4x Televue Powermate and 11mm eyepiece - this is pushing the limit of this telescope in urban skies (about 545x magnification):

The dark divisions of the rings of Saturn are visible.
Multiple bands of Jupiter are visible.
Nicely sized view.
Produces a dimmer view than at a lower magnification, however.

When using high magnification, a steady mount that is easy to aim and keep on the target is important. It's very easy to lose the target when you don't have fine control or the telescope wobbles.
Aperture isn't so important because planets are bright. Larger aperture telescopes allow collection of more light, which is useful for viewing fainter objects. That said, a greater aperture will produce a brighter view at higher magnifications. This will likely be negated by the magnified atmospheric turbulence, however.

What do I need to photograph planets?

Single exposures (images) of planets will generally appear blurry. The reason for this is that the atmosphere is turbulent and the planets are small in the sky. Even when looking through an eyepiece, Jupiter and Saturn will sometimes often be blurry and then occasionally appear quite sharp. Therefore a single photo will generally catch the planet during a blurry moment. Also, when visually observing, your brain is especially good at putting together a clearer view than is there at any single point in time, so it always appears much shaper when looking through an eyepiece.

The best approach to imaging planets is to record a video. Digital cameras will typically record 30 frames per second, and with enough footage (a few thousand frames, for example), there should be enough sharp frames that can be identified and stacked together using software such as Registax. There are plenty of tutorials online for using image stacking to produce better planetary imaging results. In my view, Registax isn't very intuitive to use, but once you know how to use it and work with the limitations, you can produce good results - for free! There are also commercial product offerings out there for planetary image stacking. Keep in mind that some stacking software is designed for deep sky objects only, rather than planets.

People also use high frame rate web cams to increase the number of frames that they can capture.

So, all you need is:

A telescope with suitable magnification (136x and above is good - for greater size and details, more like 300x).
A video-capable digital camera.
A T-mount adapter for your telescope and matching T-ring for your camera (if it is a camera that accepts interchangeable lenses). Otherwise, a regular compact camera or web cam can be fixed to the telescope as you see fit.
Some frame stacking software.
A reasonably steady mount. Note that if you don't have a polar aligned equatorial mount, videos shouldn't be too long as rotation of the view will cause the planet to be smudged when stacked (if you don't 'unrotate' the frames to align them). In this case, try a minute or so initially to see what kind of result you get.

Here's a comparison of a single exposure of Saturn versus an image produced from stacking about 2000 frames and using wavelet filtering to enhance details.

Comparison of image capture techniques for Saturn (100% crop).

With a little more practice (the image on the right was produced from the first night of trying out my new imaging scope and mount), I'll hopefully be able to produce better results. Actually, I was shooting through thin cloud at the time, but it still appears sharper than my very early attempt on the left.

Here's an older, but reasonably comprehensive article describing the stacking process:
Sky & Telescope magazine article link.

Rather than muck around with laptops and webcams, I just attach my Olympus PEN E-P3 micro four thirds camera to the telescope. You can do the same with any DSLR camera and a t-mount adapter.
I typically use Final Cut Pro (I use a Mac and use it for other video work) to export the frames from the video, then load those into Registax for alignment and stacking. Registax loads AVI video directly, but other formats will need converting or frame exporting as I do.

Planets - Lessons Learned

I was able to successfully capture images of planets using my 12 inch Dob Newtonian with a 4x Powermate. The main issue being that the scope is long (the tube is 1.4 m long) and heavy (20kg). It therefore wobbles with minimal encouragement. That said, the Alt-Az tracking on the Dob mount works well enough to keep a planet with view for long enough to walk away and fetch something or to record a video for lots of frames.

Another issue is that with the camera attached at prime focus (no powermates, barlows, lenses, or eyepieces between the cameras and scope), the Newtonian focus point is just out of reach for the moon. I tried slightly collapsing the tube to help. This worked, but throws the mirror collimation out, so more of a pain than it is worth. With the Powermate or a Barlow, this isn't a problem. Note that there are Newtonian tubes designed specifically to address this kind of problem.

Visual observation of Saturn and Jupiter, even with the 4x Powermate and a high power eyepiece produced big, sharp views when the atmosphere was cooperating.

Imaging is made easier with the RC8, however. The tube is under a third of the weight of the 12 inch Newtonian and under a third of the tube length, but with a slightly greater focal length. Makes for much steadier imaging on a given mount and the imaging train and focus point is designed for attaching cameras and other imaging related equipment.

When capturing video, your camera may not give you control over the exposure and may be just 1/30th of a second. This may not be the ideal exposure for your target (Mars appears really dull at high magnification for me when I record video like this). If you can't select a video format with a suitable frame rate, you may need to increase the ISO when recording video or else process the result frame or stacked image afterwards to make the planet brighter.

My 400mm refractor was good for viewing and imaging on an occasion when the moon was occulting Jupiter. It allowed for a wide view that included both objects when they were far apart, but approaching each other. Jupiter was of course small, but definitely a planet rather than a star. Also, this focal length was good for larger nebulae such as Eta Carina - my longer focal length scopes get a bit too close. Also, I couldn't view this at the time from my inner-city deck, so had to go mobile - hence use of the smaller scope. I didn't need a tracking mount for this because only short exposure were required.

The moon and Jupiter (on the right) with my 400mm refractor at prime focus. Slightly red due to some bush fires at the time.

Same again, but this time over-exposed in order to capture some moons of Jupiter (click for larger view).

1 January 2014

Astronomy Lessons Learned - Intro.

Starting out in Astronomy - Introduction

After much deliberation, about eighteen months ago I bought my first serious telescope. I have always had a fascination with the skies above and the universe at large, but had never made the time to work out exactly what I needed to 'do it properly'.

There's nothing quite like the first time that you see Saturn through the eyepiece! The thought that light from the sun has streamed out to Saturn, bounced off, and then landed on your own eye is amazing!

Saturn - the result of stacked frames from a video using my Olympus camera and RC8 telescope (about 291x magnification).

After marvelling at seeing the Orion nebula visually, to then see a longer exposure of it appear on my attached camera screen showing colour and even more of its vast clouds started me down the path of wanting to explore astrophotography and see the ordinarily invisible wonders of the night sky.

Orion Nebula (M42) - 60 second exposure, processed to counter 'light pollution'.

I have spent a lot of time researching online and reading numerous forum posts, attempting to piece together the puzzle that would show me exactly what I needed. More specifically, I was hoping to buy a telescope that would be versatile, that I could use for anything. The truth is, there is really no such thing, although you can get close if you accept that there will always be compromises. That said, I believe I've purchased equipment that has suited me well as I've progressed over the past eighteen months. I now have a few telescopes which are used for different purposes.

In this series of blog posts, I'll attempt to distill what I've learned both through research and through spending long hours under the night sky fumbling around with my astronomy gear.

This first post will summarise the key topics that I'll explain in more detail, and with more focus in following posts. Often I have found statements online such as "Dobsonian mounted Newtonian telescopes can't be used for astrophotography". Generally these kind of statements don't address all of your questions as a newcomer to astronomy. Through trying things out, I answered for myself the practical reasons why I would make the same recommendation. (Note however, that you can image some things with a Dobsonian mounted Newtonian, depending on how you are set up)

Start Simple

Even after having spent time with telescopes, a recent trip to a dark site (far from the city, where I live) renewed my appreciation of just looking up at the sky and seeing the Milky Way in all its glory - no telescopes required!

Many people will suggest starting with a pair of binoculars, which is not a bad suggestion. With a pair of 50mm 10x binoculars, you can see so many more stars than with the naked eye. The Orion Nebula will also start to take form as a gaseous smudge rather than just a bright star. Also, they're very easy to pick up and point anywhere which is great for learning your way around the night sky!

Visual Observing

"But ha! A telescope sounds so much better than binoculars", you say. Well, yes you will be able to see much more with telescopes by magnifying smaller objects, although you'll view less area of the sky at a time. Also, you'll be able to attach cameras more easily, although setting up a telescope and cameras takes much more time. Again, all optical instruments serve a purpose because no one instrument can do everything well.

For longer focal length telescopes, a Dobsonian mounted Newtonian is a popular choice for visual observing. They are easy to aim and the larger apertures collect a lot of light. I would say that 8 inches aperture and above can provide good views of the brighter nebulae and globular clusters. I started with a Skywatcher 12 inch GoTo Dobsonian because I did have 'aperture fever'. It provides great views, but the telescope plus base are a total of 43kg and it doesn't easily fit in my current car! It should be noted that Newtonian telescopes require mirror collimation, almost every time that you move them around. This is to align the two mirrors, which isn't a big deal once you're practiced at it, but is an additional setup step to consider. A ten inch Dob Newtonian is probably a good compromise of size/portability and aperture. That said, I found the views through my 8 inch RC8 at a dark site not too far off the 12 inch, despite being a design that people don't typically use for visual observing.

Others prefer to start with a short focal length refractor. All you need to do it put them on some form of tripod mount and they're ready to use! Generally better for wider field viewing, but a quality refractor telescope and suitable choice of eyepieces can make them quite versatile. The limitation being aperture, as refractors become very expensive at larger apertures.

If I was starting again, I'd probably start with a (maybe collapsible for greater portability) 10 inch Dobsonian Newtonian for visual observing. It would provide a large aperture and be much easier than the 12 inch equivalent to wrangle, although an 8 inch would definitely be more portable again and consequently a better choice. I wouldn't bother with electronics for visual observing, because I would know I'd eventually get a different scope and sophisticated mount for astrophotography.

In an ideal world, you should attend a star party to get an idea of what you'll see with your eye through different telescopes. If you find that you get more of a kick out of imaging colourful nebulae than viewing faint grey smudges of nebulae, you won't want to over invest in a telescope and mount that isn't ideal for photography. Better to save some cash which will easily be spent on astrophotography gear.

The saying that "the best scope that you have is the one that you use the most" is certainly true.

Astrophotography

My First Setup
Initially, I just stuck my camera onto my Dobsonian mounted Newtonian using a t-mount to see what I could see. For bright targets such as the moon, you don't need any any tracking as the photo exposure will be short.
My mount had tracking, so I could manage several seconds of exposure at focal length 1500mm (3000mm at 35mm frame equivalent) if everything went well. The problem is that the tracking wasn't designed for astrophotography, so:
1. It jumps around a bit to keep the target in viewAlt-Az mount - not good for exposures of more than a few seconds.
2. It doesn't address rotation around the poles (it isn't level with the equator) and so your target won't just move around in the view, it will also rotate because its movement will be an arc.

Also, as previously mentioned, such a big scope wobbles a lot - which prevents any real length of exposure.

What You Really Need
Many people start astrophotography with an SCT telescope on a mount that can be equatorially aligned. I don't have experience with these, but I've seen many great images produced. Myself, I use an RC8 (8 inch Ritchie Chretien design), which is a design typically used for imaging. Since GSO has started producing them, these are much more affordable now. Before buying one, I had trouble finding anyone who used them visually to comment on the quality when not imaging. I've found the views to be satisfactory and was really impressed when I took it to a dark site recently. I'd be happy to use it for visual observing rather than lug my 12 inch Dob around! The reality is, however, that my camera will generally be attached to this scope.

You need an equatorial mount that can handle the weight of your scope and camera. The general rule of thumb is to go no more than 2/3 of the stated maximum load for the mount. The reason being that a more solid mount is needed to prevent wobbling and movement due to a heavy telescope and camera and for the motors to be able to handle the load.

Then there's the camera, related gear, and image stacking and processing software which I'll discuss in a following post. The biggest thing to keep in mind is that 'light pollution' near cities means that long exposures will require heavy processing to separate the target from the general sky glow. This results in much noisier images. I live close to the Melbourne CBD and a 60 second exposure at 1600mm focal length produces a background that is definitely not black. Orion Nebula doesn't fare too badly, but fainter galaxies etc. are hopeless where I live.

Below is one of the unprocessed output images from the camera that I used to produce the final Orion Nebula image near the top of this post (after processing, stacking and then tweaking the levels). The result does look pretty good, but it wouldn't win any awards. If you look closely at the final image above, it is quite grainy due to the processing to separate the background and the nebula better.

Unprocessed image with light pollution (60 sec exposure).

Here's a comparison with Centaurus A, a galaxy that isn't much brighter than the sky glow where I live. Consequently, even after heavy processing, there's barely anything there. I'm looking forward to my next dark site outing to capture some galaxies! Note, this was taken with my little short tube 80 refractor. The results may be a little better with the RC8 under these same conditions (maybe).

Light pollution and heavy processing required to separate the subject from the background - with unsatisfactory results.

Disclaimer: I haven't owned or tried other telescope designs such as SCTs, so this based on my direct experience only.

A quick brain dump of some things that it's useful to know (and accept) when starting out:

The requirements for visual astronomy are different to those for astrophotography.
There are a number of different telescope designs, some more suited to certain uses than others, so ideally you'd have some idea of what you'd like to spend most of your time on. This will likely change over time!
There are two main mount types. Alt-azimuth mounts are easy to orient for visual observing. Equatorial mounts are essential for long exposure photography through telescopes and they require more time to setup and align properly than a simple Dobsonian mount.
When your local astronomical society has an event that is open to the public (or else you join), go along to check out other people's equipment and get a feel for what to expect with different types of gear. Astronomers like to share knowledge and tips!
The turbulence of the atmosphere limits the quality of viewing an object at high magnification.
The turbulence of the atmosphere makes it reasonably impossible to capture a detailed image of a planet with a single exposure photograph.
The higher the magnification, the dimmer an object will appear, resulting in less contrast/detail of the view.
The higher the magnification, the quicker an object will move out of the field of view (if you don't have a tracking mount) due to the rotation of the Earth.
The higher the magnification, the harder it is to find your way around the sky because you're viewing a smaller portion of the sky. You'll generally start with a lower magnification eyepiece to navigate to the right location, then switch to the higher magnification eyepiece which may require some hunting around to get the small object (planet, for example) into the view.
'Light pollution' of urban environments limits your ability to view and photograph some faint objects such as nebulae and galaxies. The sky glow can be brighter than the objects themselves.
Heavy and long telescopes will wobble when you touch them and when there's a breeze. When viewing at low magnifications this isn't a problem. At high magnifications (for example, when viewing a planet), you're viewing such a small portion of the sky that even the smallest telescope movement will noticeably jiggle the target in the view. For astrophotography, this is a showstopper.
The moon is super-bright. Use a 'moon filter' to reduce the brightness for visual observing. It will be more comfortable and you'll see more detail.
If you're interested in astrophotography, learn to use the manual controls of a camera (DSLR, for example) with a telephoto lens first. Using a telescope instead of a regular lens multiplies the degree to which everything must be perfectly setup. Target the moon and interesting sections of the Milky Way. My first attempts were handheld shooting of the moon with a 150mm lens (quickly followed by use of a tripod).
To image objects that require a long exposure (greater than a few seconds), you'll need an equatorial mount. Typically, anything other than the moon, short exposures and video clips of planets, and regular sky views with a wide angle camera lens.
Equatorial mounts are a pain to setup and polar align in order to capture exposures of beyond 30 seconds without creating star trails (and consequently 'smudging' whatever your target is).
Collapsible Newtonian telescopes are more portable, but generally require collimation every time you move them.
A Dobsonian mounted Newtonian without electronics for GoTo and tracking is probably the best value option for being able to view a wide variety of objects visually.
GoTo mounts are pretty handy, especially in the city where light pollution makes it harder to navigate visually. That said, if you can't get your mount aligned correctly, then GoTo won't go to where you're hoping it will.
Tracking is nice to have when you're operating at high magnification, even if you're not imaging. It's not essential for visual observation, but it's good to not lose a planet out of the field of view if you look away for a few seconds.
Wide aperture telescopes (12 inch Newtonian, for example), provide impressive views of fainter objects, but are big and heavy and therefore less portable and more of a hassle to use.
You don't need a large aperture for astrophotography, because you rely on longer exposures in order to collect more light. However, a larger aperture will require a shorter exposure and therefore less accurate tracking. If you need a long focal length telescope, some of those designs (SCTs and RCs) naturally have a larger aperture with the longer focal lengths.
There's no substitute for a dark sky if you want to capture quality long exposure images of deep sky objects. You can get some reasonable, although grainy results by heavily processing long exposures in skies with high light pollution.
There are desktop and mobile 'sky atlas' applications that can help to locate objects and also work out the size of objects in the view of various telescope and eyepiece combinations. I use Starmap Pro and Starmap HD regularly.
astrobin.com is a good site for viewing user uploaded astro images. You can search for specific astronomical targets and see which equipment was used to capture them along with exposure details. Keep in mind that there are people out there with expensive gear getting some impressive results, but also amateurs with modest equipment who have also honed the techniques allowing them to produce great work.