AnnMarie's Blog

My plan: to use a Starlight Express Lodestar & 300mm mirror lens to provide guiding for both a 6″ Celestron SCT & a variety of Canon lenses. The problems: how to put the camera & lens together and then how to mount them securely to the dovetail & CG5 (ASGT) mount. The solution? A Mogg adapter!

That’s right, all the way from Australia in only ten days from when I ordered it, the much anticipated adapter arrived last weekend. It’s bottom right in the picture above, the other items being: Manfrotto mount plate, Lodestar camera & Super Paragon 300mm f5.6 Mirror Lens. The adapter is light but sturdy and has a tripod mount thread in its base.

The Lodestar’s type ‘C’ thread screws neatly onto one side of the adapter whilst the lens’ Pentax bayonet fixes to the other side. Using the Manfrotto plate the whole assembly can now be fixed to the bottom of my dual camera mount dovetail (see previous post for details). The picture above illustrates this setup. It can also be mounted directly to the C6SCT tube via the Piggyback camera bracket. The complete solution is light & rigid enough for this to be a secure & balanced fitting. It was in this (SCT) guise that I tested it last night, as in the picture below:

It’s been cloudy here for weeks but last night there was a clearish gap between 2-30am & 4-am. Typically it was the night of the full moon (see picture above)  and misty with it, so no deep sky imaging but plenty of time for testing the camera/lens performance. As promised by Mogg adapters the adapter dimensions are just right for obtaining infinity focus with some adjustment room both ways. What to image? Well the moon seemed like a suitable test subject …

I’m quite pleased with that as a single test image and when picking a star as the target, the computer confirmed good tight focus too. Now what I really need are some beautiful clear nights; I’ll keep dreaming

Technorati tags: Guiding, Mount, Celestron, Astrophotography

For sometime I’ve been intending to build myself a sturdy dual mount and all the recent cloudy weather has left me with the opportunity. I wanted to be able to put 2 cameras onto my CG5 equatorial mount, both with similar alignment. The system needs to be rigid yet very quick to change over between configurations. Typical immediate combinations might be:

• Digital SLR plus Starlight Video Camera
• Digital SLR plus Lodestar guide camera

In the future it might also be asked to carry an astro CCD camera attached to a Canon Lens. Having been pleased with Manfrotto equipment for my daytime photography, I decided to base the plan on their accessories; here’s the starting point:

• Over length dovetail to fit mount – in my case the CG5
• 1/4 inch 20tpi & 3/8 inch 16tpi UNC head cap screws or bolts (to fit std & pro photographic tripod fittings)
• Manfrotto 323 Quick Change Plate Adapter
• Manfrotto 357 Universal Sliding Plate

The Manfrotto quick fit plates are really very secure devices with safety clips too. If any slippage does occur there are also compatible Manfrotto anti-twist spotting scope plates available. At this point can I also recommend Stagonset fasteners to anyone in the UK who is looking for good quality fixings like the UNC cap screws.

Now to put it all together. I drilled an extra hole in the dovetail at one end to take the slide plate fixings. Originally I had intended this to be 3/8 but I decided that might weaken the dovetail too much, so the slideplate thread was reduced to 1/4 with a bronze insert and then a 1/4 fixing was used. Spring washers were used to ensure a substantial hold. I also replaced the smaller screws that were supplied with the dovetail, these give extra purchase to remove any risk of movement. Here’s a picture:

Next the procedure was repeated at the other end of the dovetail, to mount the quick change plate but on the underside this time. The whole setup was now checked for alignment and then the fixings tightened right up. Here’s a picture of the complete assembly:

I was then really lucky, in that the next night I had just a one hour break in the clouds so I could briefly try the thing out. Everything seems very secure, the slide plate allows me extra adjustment to find good balance with a large lens & DSLR whilst the bottom quick change plate works well giving plenty of clearance for the smaller camera. Below are two images of the setup that I tested it with, Canon 20D 100-400L plus Mintron & C lens:

A quick word about the Mintron starlight camera, this is a fabulous piece of kit. If you have children who want to see the view or maybe a group of friends around for a party, this really beats everyone queuing up & squinting through the eyepiece. It is highly sensitive & can internally stack up to 128 frames realtime whilst outputting this video to a TV screen. Below is an image of the plough (big dipper) on TV from the other night (apologies for poor quality but TV screens don’t photograph too well)

The Mintron’s C lenses are interchangeable & it can also be attached to the back of a scope too. Perhaps I’ll do a separate write up on it, after I’ve captured some video with a capture card. I have seen a perfectly respectable M27 with it on the back of the C6SCT and Tamsin certainly loves viewing with it.

So that’s that for now, I’m currently waiting for the arrival of my adapter to mount the Lodestar & 300mm mirror lens together. Once that’s made it here from Australia, I should be able to start guiding. If only the skies would clear …

Technorati tags: Starlight Camera, DIY, AstroPhotography

A little time ago I wrote an article for a Home Education magazine. It was a light look at how I started taking pictures of the sky and how others could easily join in. I thought this might be worth posting to my blog – so here it is …

    A sight to stare at. Early morning at home, after a night’s astrophotography.

“Always got her head in the clouds”

I was six years old and sitting in the classroom of my local village school. It had a large window which looked out across meadows & farmland. Today was summertime and I was watching the buttercups nod in a light breeze, bathed in a beautiful golden sunshine. My mind wandered, how amazing it all is from the beautiful flowers to the Sun and heaven knows what other fascinating things in the sky above.

“Jones!” yelled the teacher,”You’re not listening!”

“I am Miss” I replied, followed by a verbatim quote of the last 30 seconds of her lecturing.

Then I was punished, for showing off. I never really did get the attitude of schools & some teachers. What I did have was a fascination, a curiosity for all things ‘nature’, including the sky. Here started my voyage into Astronomy & Cosmology.

If you’re out under a clear dark sky one night soon, move away from any artificial light, turn off your torch and stare upwards. Your eyes will gradually become accustomed to the dark and more stars will come into view. Look for the milky patch across the sky, that’s the Milky Way, our own galaxy. It contains about 200 billion stars. The Universe beyond? Well there’s more stars there than all the grains of sand on all the beaches of our planet. And stars don’t account for half the matter out there.

Pictures & a thousand words

Another interest of mine is the use of cameras. I guess it really developed when I was a teenager but I have only fully indulged it within the last decade or so. Photographs can record a moment in time, a memory, that’s what most of us use them for. But that’s not all they can do. Some use them to provoke strong emotions, more than any passage of pros might do; take anti-war journalism for example. For others, the camera can show us sights that our eyes can’t – this is where one of my interests lies. Freeze the motion of a running animal with a fast shutter speed, take a macro shot of an insect feeding on a flower, point the camera down a microscope to reveal the tiny world around us; all these techniques & more, expand our awareness, our comprehension of the things around us. I suppose it was only a matter of time before I wished to put camera & telescope together.

If you have a camera that can take long exposures (more than say 30 seconds), take it out on a dark starry night, put it on something secure preferably a tripod, set the zoom to wide angle & point the camera upwards about 50 to 55 degrees (in the UK) & northwards. Experiment with the exposure time but start with 15 minutes or so.

The resulting image will show stars apparently rotating around a point (the celestial pole) in the sky. You’ve just taken your first astrophotography picture and have also demonstrated the spin of our planet on her axis!

With just a camera & tripod you can also take good pictures of the moon, aurora (if you’re lucky) and even record a few planets (Venus, Jupiter, Saturn, and Mars) but they won’t look very big, for that you’ll need a telescope.

Stardust Fairies

Tamsin (our daughter) has, like most children, a wonderful imagination and it helps her jump from one thought to another. This was the case here. She had been thoroughly enjoying reading a series of books about “Stardust Fairies”. Within the tales, each fairy has their own special star; Regulus being one of them. Tamsin wanted to see Regulus (Alpha Leonis) so we checked on its positioning, first star of the constellation Leo, and pointed it out to her. Did you know that Regulus used to be called Cor Leonis, the lion’s heart, so it’s a star for all you courageous home-ed families out there.

We then became involved in a project to survey the darkness of Britain’s skies. To complete the survey you needed to count the number of stars that you can see in Orion’s belt. Tamsin loved it and from here it was but a small step to her wanting a telescope to further her interests in Astronomy.

We bought a 6 inch Schmidt Cassegrain (SCT) scope & an equatorial mount to put it on. There are several different types of scope; the SCT is probably the jack of all trades. It is good for planet viewing & deep sky objects and suited to visual or photographic use. The equatorial mount allows the scope to slowly track across the sky counteracting the rotation of our planet (as you photographed above).

The Low Down

So what do you need to get started? Well the great thing about astrophotography is that it’s easy, simple & cheap; it’s also difficult, complex and expensive. Did you get that? What I mean is that this is an interest that you can start off easily and grow it to become as involved as you wish.

Obviously some sort of camera is a necessity, your current one is probably sufficient for getting started. Modern digital cameras are great, they give you immediate feedback, are fairly sensitive and many have access to multiple settings. Read on for details of different techniques and what’s involved.

The Moon	Setting Sun (with sunspots)

Please note: never look at the sun or image it without specialised filters – it could blind you.

Techniques

Wide field

Just a camera & lens can be used to take a broad picture of the night sky. Short exposures can be made on a tripod but longer exposures will need some sort of tracking mount. This can be as simple as a ‘barn door mount’ (search the web for plans on how to construct this for about £15) but is frequently done by ‘Piggybacking’ your camera on a telescope & mount whilst tracking. This requirement to track the sky for exposures above a handful of seconds is common to all astrophotography where you don’t wish to see the effects of Earth rotating.

Afocal

Your telescope is all set-up and you’re viewing an interesting site through the eyepiece, the simplest way of recording this is t
o hold your digicam to the eyepiece & take a picture. There are things that you can do to refine this:

· Buy a digiscoping adapter to firmly hold your digicam to the eyepiece ~£30

· Match your camera lens to a suitable widefield eyepiece, specialist ones are available

· Set your digicam’s aperture wide open

· Use your digicam’s manual focus, set it to infinity & focus with the telescope

· Use a remote release or your digicam’s internal timer – avoid vibrations

Most of all experiment with different settings & targets, get to know what effect each change makes and have fun.

Prime

This is the main technique for serious astrophotography. The telescope is all set-up and the camera is attached via an adapter directly to the telescope. There is no camera lens between scope & camera; the telescope focuses light directly on to the camera’s sensor or film. The camera itself may be a SLR (Digital or Film), a specialist cooled astronomy CCD, or in some cases a webcam type video camera.

   A collection of Messier objects

SLR

Most people would accept that the Digital SLR now has an advantage over film. You will need a ‘T’ adapter for your camera make, to attach it to the scope camera adapter. You will also need a remote shutter release cable. The ability to connect the camera directly to a computer is also helpful. A 90 degree viewfinder attachment can also help to avoid the need for limbo dancing lessons. (That or a good osteopath). Focusing can be awkward – autofocus is unlikely to work for all but the brightest objects. It is best to find a bright star & focus on that, then leave the focus alone for the night if possible – do take a test shot to check your focus. There are computer programs that can help you with this. Also worth noting is that most standard cameras have an infra-red filter (needed for normal daylight photography) and this reduces their astronomical sensitivity. Only Canon have made a specialist astronomy DSLR, the 20Da, but several conversions are available, particularly by a company called Hutech.

Astro CCD

These devices are very sensitive to light; they are typically cooled to 20 degrees below ambient for noise reduction. They are however, very expensive & can only be used for this one purpose. At £1000 – £4000 this is definitely the hard core end of the hobby. They are controlled from a computer and can produce stunning images. Imaging is usually done by taking four sets of images using a filter wheel, 1 set for luminance & then 1 each for Red, Green & Blue; however ‘one shot colour’ CCD’s are available. Do not however under estimate what can be achieved with a DSLR.

Webcam/Video

This is a relatively new technique and is especially suited to planetary imaging. A short spell of video, perhaps 1000 frames, is recorded straight to PC. Each frame is then analysed by a computer program and the best are stacked together to build a detailed image. The advantage of this is that moments of good ‘seeing’ (I.e. when the atmosphere is still) can be caught and used, whilst more ‘wobbly’ moments can be discarded. The standard software for analysis & stacking is called Registax. You can build your own camera or buy a commercial one such as Celestron’s Neximage (about £90).

CCD / DSLR Processing

Typically when imaging a deep space object (DSO), you will be taking multiple exposures of the object. These exposures are called lights and they will be stacked together in a computer to create a far more detailed image. You should also be taking exposures called darks & flats. Darks are taken at the same temperature & settings as your lights, these will be used to correct the lights for hot pixels & circuit noise. Flats are taken at the lowest ISO setting of your camera and are of an evenly illuminated object, a lightbox or the evening sky just after sunset. These flats are used to correct your lights for vignetting and dirt on the imaging train. You should also take darks for the flats, no I’m not kidding! There’s various software available to help you with this process some commercial some freeware, Deep Sky Stacker is an easy start but my preference is for Iris.

Telescopes

I am not going to go into telescope choice very deeply here, everyone has there own preference & budget. But there are a few pointers:

· Don’t buy a Department Store special, do buy a proper astronomical scope

· Refractors will give you stunning sharp images but they’re expensive per inch of aperture and you’ll want an APO version to keep colour issues to a minimum

· Newtonians are cheap for large apertures but don’t always convert into a photographic instrument without hitches

· Catadioptics are a large group that inhabit the middle ground and are my preference, there are different types:

o Maksutovs are good visual instruments but can be a bit slow for imaging

o Schmidt-Cassegrains are a good all round scope that won’t break the bank, this was our choice.

o Ritchey-Cretiens are the desire of many an astrophotographer. Not cheap but superb for imaging – this is the basic design of Hubble.

   6 inch SCT with piggybacked 400mm Canon lens – all on CG5 equatorial mount

Guiding

Sooner or later you may wish to take images that require an individual exposure time of more than a minute or two & a reasonably long focal length e.g. 1500mm or more. At this point the tracking of your telescope mount may not be accurate enough, now you need a guiding system as well. This will either manually or automatically correct the telescope position at short intervals, on top of the equatorial tracking. The details of this are many, definitely beyond the scope of this article but you should be aware that several methods exist and there are several interest groups on the internet that will be willing to advise you.

Summary

I have tried to give you a brief outline of Astrophotography. There are many wonders to see, they are inspiring, they put us into our proper perspective and they are beautiful. A telescope alone is a fantastic resource for any home educator, but add a camera to the plot and you will see many more beautiful wonders.

Resources:

Books:

Stardust Magic by Moonlight                                  Linda Chapman   ISBN 0141317795          Well, it inspired Tamsin

Starware                                                                     Philip Harrington   ISBN 0471418064          A guide to all the kit

Digital A
strophotography The State of the Art   David Ratledge      ISBN 1852337346          You really need this book

Stars & Planets                                                          Ian Ridpath            ISBN 0751327123          Finding your way around

Astronomy for Dummies                                         Stephen Maran      ISBN 0764584650          A crash course in the basics

What are you waiting for? Go put your head in the clouds.

I’m still learning, in fact I hope I always will be. However, I think this may be a good point in my journey to put down some details so that others who are starting out on this fascinating path can pick up a few pointers & ideas. There are some excellent tutorials out there and I’m not going to compete with them; rather I’m going to tell the story of my recent M31 Andromeda image, with a few extra details.

Imaging Aims –  My aim when taking this image was to produce a sharp image with a realistic hue. The image should show the extent & detail of the galaxy with dark dust lanes, star clouds & globular clusters. The core of the galaxy should not be too burnt out and the image should successfully print out at A4+ for framing. Here’s a reduced sized version of the final image (in case you didn’t see my Andromeda post) :

  Click image for a larger view

Equipment -  Everything should start with a solid basis and never is that truer than in Astrophotography. A solid tripod or pier with a decent mount atop is the prerequisite for any imaging of DSO’s (Deep Space Objects). The mount will need to ‘track’ the sky ie counteract the rotation of our planet. On this mount will be your imaging system, a camera & lens system. The camera maybe a simple compact digital affair, a webcam, an SLR or a specialised astro CCD. The lens system may be a variety of telescopes or even quality camera lenses. Computerised control systems can also be added; as can guidance systems that greatly improve your ability to take long exposures. Discussions about equipment can be found elsewhere; suffice to say that I mainly use a Celestron AS-GT mount, Canon 20D camera and either a Celestron 6 inch SCT or a selection of Canon lenses. I have no guiding system at present. For this image I used the 20D with a Canon 100-400 L IS lens set at 300mm f5.6 and mounted directly on the AS-GT.

  Mount, Scope & Camera with Lens

Technique – The basic technique employed here & for many astrophotos is to take many short sub exposures and then stack them together to make the final detailed image. For an interesting discussion on short sub-exposures visit Samir Kharusi’s website. Put simply, the benefit of this is to drastically increase the signal to noise ratio of the final image whilst allowing the demands on tracking / guiding to be reduced. To illustrate the point I have done a simple unregistered luminance add of my 1.5 hrs worth of subs, this is what the image would look like without using a stacking procedure, see below …

  Not a pretty sight

Planning – Next we need to select our target, check that it will be visible for long enough and calculate what focal length will be best for the object; may I suggest AstroPlanner as an excellent piece of software for this purpose. To help general visualisation I would also suggest a Planetarium program such as the excellent freeware Carte du Ciel.

Set-up – As routine before imaging we should have aligned our mount to the celestial pole and adjusted the balance so that it is almost perfect but just a little heavy on the side pointing eastwards (this encourages the tracking to be slightly tighter).

Now we should pre-focus the camera on a suitable bright star; I’ve come to know Vega quite well, this summer. There are various automated computer programs to help but I currently use a visual diffraction focusing technique always followed by taking a test shot. This done we can now find & frame the object that we wish to image. The AS-GT mount has a very useful feature called ‘Precise Align’, if you have this mount then I recommend you use the function. With the object aligned take a test shot this will allow you to double check the framing of the object & to estimate the required camera settings.

Camera Settings – So what total exposure time do you need? What length sub exposures? And what ISO setting. Through trial & error I have found that ISO 1600 on the Canon 20D appears to suit my imaging best; ISO3200 gives a lot of noise but ISO800 gains me no quality improvement over 1600. Total exposure time – well looking at other astrophotos will give a good guide, experience has to help too and don’t forget to check out the magnitude of the object, if its available in a sky catalogue. As for sub-exposure time well I’m a little more scientific over that …  Your sub needs to be long enough that the fine details are recorded above the background noise level but not so long that your mount runs into significant tracking errors. Take a test exposure and review its histogram on either the camera back or a PC.

  The histogram for one of my M31 subs

If the histogram looks similar to the one above then your exposure should be fine, in general aim for the lefthand edge of the spike to be 1/3 to 1/2 of the way from the left of the histogram – this lifts the detail out of the noise zone without blowing the highlights. Now is the time to have a check for tracking issues, are the stars nicely round, if so then we’re ready to go!

Image Capture – We now can set the camera to work and allow it to accumulate the ‘lights’ that will make up your full exposure time. I find it useful to use Canons TC-80N3 programmable remote control, just tell the camera to take x many exposures y seconds apart and let it go. Now’s the time that you can go have a cup of coffee or two but do watch out for rain or any other problems. Alternatively, if you’re capturing to PC then you could give AstroScopius a go and watch as your image integrates in front of your very eyes!

As well as lights you need to capture dark frames & flats. Darks are simple, just put the lens cap on and shoot a few frames at all the same settings, including temperature, as the lights. These darks will be used to correct for hot pixels & noise. The flats should be taken at the lowest ISO setting possible and should be of an evenly illuminated white object I have successfully used the dawn sky, a lightbox and a magi-whiteboard with fluorescent strip light illumination. The histogram for flat
s should show a spike as far to the right as possible without overexposing anything.

  Histogram for the flat field

Looks like I had room to expose this flat a little further but it worked fine anyway. The flats will be used to correct for errors in the imaging train such as vignetting & dust bunnies. You will also hear of bias or offset images, these are used to correct for permanent sensor pattern issues but I have found it unnecessary to use more than a synthetic bias file, created at the processing stage.

So its now dawn, you’ve been up all night and what do you have to show for it? A bunch of light dark & flat files, none of which look like you’d wish the finished image to be. I had 45 lights of 2.5 minutes each (but I chose to discard 8 of them) 10 Darks 5 Flats & 5 Flat Darks. Examples below (Light, Flat, Dark) …

Click on the light file (left) to see an enlarged version.

 What to do now, my advice – get some sleep before starting processing

 Processing – There are many different methods & programs to process your raw images; here I shall give an overview of what I did for this image:

I have tried several different programs for the scientific initial processing, some pay some free, and have found none better than Iris. Whatever program you use, good image organisation is useful; with Iris it is vital. The program has a working directory where it will save all files including a copious amount of working files, probably several gigabytes worth. I use a striped drive (for speed) with a separate working folder for each project, as per the screen capture on the left. 

The next few stages are all done in Iris; if you are going to learn it then may I suggest reading the tutorials on Christian Buil’s site and for a detailed walk-through you will find Jim Solomon’s Cookbook an excellent resource. Here is the basic process:

• Discard any dodgy lights due to clouds, airplanes, etc.
• Import good RAW files
• Create master dark & flat files plus synthetic bias & cosmetic files
• Correct the lights by applying the darks, flats & bias to them.
• Register the files, so that stars are all aligned
• Crop out the edge overlap caused by aligning the files
• Normalise the files to equalise their background
• Stack the files to produce 1 file with all your data in it

At this point you could move on to another program or do some more processing in Iris. I did the latter, first correcting the white balance, using sub 1 ratios to avoid burning out any highlights, typically the ratios are 0.98R 0.50G 0.63B when I’ve used the 20D. I then experimented with both dynamic & colour stretches, finally deciding upon a relatively moderate asinh colour stretch. Final things in Iris were to adjust the visualisation and save my output to file – in this case a full depth bitmap file.

Next I moved into PixInsight which is convenient because it reads the full depth of an image produced by Iris without needing to adjust the levels as would be required in Photoshop. There is a significant overlap in functionality between Iris & PixInsight and while I prefer to use Iris for most things, there are a few functions that I am, so far, better at using in PixInsight. These include the two that I used here:

• HDRWavelet Transform to extract high dynamic range data within the galaxy, in this case it took 2 transforms one of 4 iterations & the next a single iteration. The output was rather too harsh for my liking so it was blended with the original in Photoshop.
• Finally a morphological transform to control the distracting starfield between us and the target. Again this was layered and blended using a mask in Photoshop so as to maintain clarity of the globular clusters within Andromeda.

The resulting layer blends were finally flattened in Photoshop before export as a 16bit Photoshop file. The final stage for all my images, astronomical or not,  is in Lightroom. Clarity, Vibrance, Curves, Colour Temperature and more can all be fine tuned losslessly in Lightroom. Not to mention it is efficient at outputting to 8bit jpg for posting on the web. In this case I needed to do very few final tweaks (minimal clarity & sharpening) and the image is as at the head of this post.

I should point out that this is an overview of the processing that I did – in reality the image & processing evolved over the course of a fortnight as I tried out new ideas. Sometimes I’d leave the image open on my desktop so that I could glance at it & think “hmm, I’ve not quite got x right” and so forth. I think that’s the thing this should be a fun adventure and one of learning too – no rush, no competition just fun learning.

I hope that this post will help a few people who are starting out, to be able to take a step forward with their imaging; it has definitely been useful to write.