Astronomy and DSLR Astrophotography Blog

In this part we’ll take a look at some telescope specifications. It’ pretty common question what’s the best telescope for astrophotography. The answer? Such a telescope doesn’t exsist. There are several different telescopes available on the market and every serves its own purpose.

The Newtonians, for example, are very handy and good instruments for astrophotography, though they need to be collimated very precisely and often. On the other hand ED and APO refractors are better, but they are much more expensive. The SCTs are compact and provides longer focal lengths but they are rarely well-made.
So the question is what telescope to choose for deep-sky astrophotography with DSLR camera?

There are several different answers, depending on our object to be captured. Let’s start with the largest: wide-field images of the sky. If you are planning to capture the wide-field images of the night sky you don’t need the telescope but the lens. This is because telescopes are optical instruments with longer focal lengths and that means smaller field of view (FOV) whereas the lenses has a really wide range of focal lengths, from 4mm up to 1200mm and more. The most common target in this range of objects is the Milky Way. This kind of astrophotography is especially appropriate for beginners because the auto-guiding is not necessary and most of the cameras already comes with “kit” lenses which have wide field of view.
One of my images of Milky Way in Cygnus taken with 50mm lens:

Mosaic of Milky Way taken with 50mm lens

Next step are large deep-sky objects. For this objects I recommend the middle-sized APO and ED refractors (80-120mm) or telephoto-lenses. If we have a good mount we still don’t need auto-guiding at this focal length but in most cases it’s better to use it if possible. The most common objects in this range are constellations, detailed locations of Milky Way, large nebula complexes (Orion) and bright comets. The next picture represents Comet Holmes as it was seen 8th January, 2008, taken with Canon EF 70-200 f/4.0 lens:

Comet Holmes with Canon EF 70-200 f/4.0 at 200 mm

Next are middle-sized deep-sky objects. The best focal lengths for them are from 1000 mm to 2000 mm. Newton telescopes and larger refractors has the most appropriate specifications for imaging this type of objects. The auto-guiding is really necessary here because just the best mounts can slew accurate enough to assure the pin-point stars at these magnifications. In this range we find almost all the object from Messier’s catalogue and the brightest NGCs. One of my pictures taken with Orion Optics Europa 8″ f/4.5 are Pleiades.

The last type of object, accessible to amateur astrophotographers, are smaller deep-sky object. They are mostly galaxies and planetary nebulas. Because they are small, we need long focal length to capture the details inside them. The SCTs and other catadioptric telescopes are the most appropriate for these objects.

So, now you know which objects are in the range of your equipment. I hope that you enjoyed reading.

astrophotography APO, astrophotography, camera, deep-sky, images, mount, nebula, telescope, tutorial

So let’s continue with the tutorial. The last time we have chosen the object. Today we will take a look at some common camera settings for astrophotography. In this tutorial I will be using modified Canon Rebel XT (350D). Modified means that I have replaced original filter in front of CMOS sensor with replacement filter of Baader. I have listed some good guides how to do it here.

Let’s go back to the topic. The camera is important piece of equipment since it’s capturing the light. Not all the cameras preforms the same but there are some common setting that it’s good to setup before we go out under the stars.

The very first thing is the photography mode of the camera. Here we have just one choice – M (Manual) mode because of one simple reason: DSLRs are not meant to be astrophotography cameras but daylight cameras. So the longest exposition that automatic modes enables us it’s 30s. But that’s far not enough for deep-sky astrophotography. We need longer exposures and the M mode has a “bulb mode”. That means that the exposition is as long as the shutter is pressed on a camera. Of course, we cannot hold the button on a camera for 5 minutes so the wire trigger is necessary.

We select M mode

The second thing is mirror lockup. Almost all the DSLRs enables lockup function. Mirror lockup means that the mirror in the camera, which reflects light to the viewfinder, locks up some seconds before the start of exposition. And why is that so important? Because if you are using telescope with long focal length, then every single tiny movement is noticeable on a picture. And when the mirror “jumps up” it shakes the system and bright stars get tails and that’s what we obiously don’t want to have on the pictures. So the mirror lockup function triggers the mirror some seconds before the start of exposition so the system can settle down before the exposition is started.

Enable the mirror lockup function

Next important thing is ISO speed. This one is still a hot topic among astrophotographers since some claims that lower ISO is better and others who prefers higher ISO settings. Anyway, two years ago I have made a test on Youth Astronomy Camp which revealed that Rebel XT preforms the best at ISO 800.

Selecting the ISO 800

For additional processing it’s the best that we use uncompressed data so the RAW mode is the right decision. If you prefer having JPGs also, then you can select RAW + JPG.

RAW (uncompressed) format

Another not so important thing is LCD brightness. I strongly recommend to set this as low as possible because in the night our eyes are adapted to the dark and if you want to check for example the sharpness of the images on LCD with the full brightness then you’ll get blind for some minutes.

The last but not the least function is information LCD illumination. This function enables you to see the settings specified in the dark. Just press the button.

Info LCD illumination

Thank you for reading. So far we have chosen the object and specified all the camera settings.

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The very first thing we have to do when we start an astophotography is to choose the object. We have to know what are benefits of our equipment, what we are planning to capture, what is FOV (field of view) of our telescope and camera, how “deep” our system goes and so on. Let’s take a look at some of this questions.

When we are deciding which object we will be capturing we can help ourselves with different astronomy software. They display imaginary sky and we can take a walk into nigh sky, choosing the objects, checking the rising, setting, magnitude, distance, … All this parameters are important when we are selecting the target for astrophotography.

There is a lot of different programs available on the web for astronomy. Some are free and others are paid. There are some of them:

• Starry Night
• Hallo Northern Sky
• Cartes du Ciel
• SkyMap
• Stellarium

In this tutorial I will be using Starry Night. It is paid but it offers endless of useful options like FOV and has  really a huge database of objects.

First of all we have to know what type of object is appropriate for our astrophotography setup. The predispositions for deep-sky astrophotography are:

• Telescope of telephoto lens
• Mount for tracking that tracks very accurate (under 2″ of error) or has option of auto-guiding
• DSLR or CCS camera with remote control of exposition

In Starry Night we put the parameters in the the section Equipment:

Then we select FOV of our telescope and camera. The program displays us the rectangle that out astrophotography setup “sees”.

So, what’s next? We have to choose the target that we are going to capture. Here are some basic directives:

• Make sure that object is in the field of view at least 3 hours in the total darkness. It has to be at least 15-20° above the horizon all the time of the capturing. Make sure that you have specified your date/time and location accurately!
• Make sure that object roughly fits to the field of your telescope’s view. The rectangle that we have specified before helps us at this step. Make sure that it is not too small – it doesn’t make any sense if you are photographing a very small planetary nebula at 600mm of focal length.
• Make sure that it is not too dim. Almost all the objects from Messier catalogue are OK, and all the bright objects from NGC makes good target as well. If the object is dimmer than 10th magnitude then bigger telescope then 8″ is recommended.
• If you don’t have GoTo or it’s unreliable then make sure that you are able to find the object in the night sky. Help yourself with bright stars, print the carts out.
• If you are using german equatorial mount then make sure that object doesn’t pass the meridian during the planned time of capturing.

Some good objects to start with: M45 (Pleiades), M42 (Orion Nebula), M44 (Beehive Cluster), M27 (Dumbbell Nebula), NGC7000 (North American Nebula), M31 (Andromeda). They are all bright and easy to find even with binoculars.

And here we are. We have the object.

Next time we will take a look at the conditions in the athmosphere that affects to the astrophotography – the weather, seeing, transparency and more.

astrophotography astronomy, astrophotography, camera, deep-sky, equipment, guide, mount, telescope, tutorial

I have decided to publish step-by-step how-to tutorial for astrophotography beginners. It’s International Year of Astronomy and I am pretty sure that there is a lot of people who are interested in astronomy and astrophotography, but they don’t know where to start.

Weekly I will publish articles guiding you trough the process of astrophotography – from equipment to the imaging tips and processing of images on the computer. Each article will cover specific part and every single of them is important for good results.

There are several different types of objects up there and they require different type of equipment, capturing, processing. In this tutorial I will focus on deep-sky astrophotography with DSLR camera and with amateur equipment in range up to 5.000$. If you are beginner – don’t be afraid! There is a possibility to start astrophotography with much lower budget and get stunning results. You just need to be patient and don’t give up.

Contents:

• Part I: Choosing an Object
• Part II: Camera Settings
• Part III: The Telescope

Don’t forget that we all learn from mistakes. With patience and enthusiasm everything is possible. Enjoy the Universe and Clear Skies!

NGC6888 - The Crescent Nebula @ Primož Cigler

astrophotography astronomy, astrophotography, deep-sky, equipment, guide, images, milky way, nebula, stars, tutorial

As we all know the optical system needs to be clean to provide very sharp and contrast image. All the small ‘dirties’ and dust affects to the image quality and reduces it.

If we use our telescope for night observations or astrophotography then the dust is collected on the optics in time. To get the best of our telescope we have to clean it sometimes. It is very important that we do that very carefully because we won’t be able to repair any of the scratches we may do during the cleaning.

Today I’ll give you some important information how to clean the primary and secondary mirror of the Newton type of the telescope.

Before we do anything we have to prepare some things we will need during the cleaning:

• Clean kitchenware that is larger at least 50% then diameter of our primary mirror fulfilled with warm water and a bit of detergent
• A clean towel
• Distilled water (approx. 1L)

Disassembly:

First of all we remove the primary mirror. We unscrew the screws which holds the cell of the primary mirror in the tube (Picture 1):

Picture 1

When we do that we carefully (!) remove the cell of primary mirror. There are different types of primary mirror holders so we have to figure out how to remove the mirror from the cell (Picture 2):

Picture 2

The disassembly of the secondary mirror is easier. We just unscrew the screws in the spider and that’s it. Just make sure that you are holding the secondary mirror all the time with one hand while with the other you are unscrewing. Otherwise it may happen that the secondary mirror falls to the floor and broke up.

Cleaning:

When we are sure that we removed all the parts which holds the glass we pick the mirror (Picture 3) and put it into the kitchenware with warm water. We just let it in it for some minutes. After that we grab it with both hands and starts moving it left and right in the water and all the dust will just flew away. We are doing that for some minutes. If we can still notice a dust on a mirror we can remove it by soft circle movements on the glass, but be careful here! Everything you should do in the water (Picture 4):

Picture 3

Picture 4

When we are sure that there is no longer dust and dirt we take the mirror out of the kitchenware and wash it with a distilled water over the bath. After that we don’t touch the mirror surface anymore. We just put it on a towel and let it to dry.

The same procedure we repeat with the secondary mirror (Picture 5). Anyway, it is not necessary that we remove the mirror from the holder because often it is glued to it.

Picture 5

After both the mirrors are dry we assemble the telescope back. We just need to be careful to make everything just in the back order we disassemble it. If we have done everything OK then our optics is prepared again to provide the best image quality!

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There are several different types of equatorial mounts but surely the German Equatorial mounts are the most popular among amateur astrophotographers and astronomers. Let’s see why?

At German’s type of the mount we have two axis: one is parallel to the Earth’s rotate axis and another is rectangular to it. This is because when the mount is tracking there is no need to move both axis as the same time but just one. This makes those mounts so popular and useful because in theory you need just one motor to track the moving of the night sky. You also don’t get any other errors like field rotation or similar.

The axis which moves from east towards west is R. A. (Right Ascension) axis and the another one that enables us to move telescope from South to North is named Declination axis.

At this version of mount we need counterweights to balance the whole system. This procedure is very important to do it as precisely as possible because the better balanced mount slews better!

When setting-up we have to do everything in the right order to assure that in the end our mount tracks as precisely as possible:

1. Put the tripod to the flat and solid ground.
2. If you are using tripod make sure that the leg labelled with “N” (North) is positioned right to the North. Help yourself with a compass.
3. Attach the equatorial head to the tripod or pier.
4. If your mount has a polar finder check the time and a date, rotate the two wheels on the R. A. axis to the right date and time and check the position of Polaris (Northern Hemisphere) or the Southern Cross (Southern Hemisphere) in the polar scope and align the stars with the marked positions.
5. If necessary do a drift-align (the guide how to do it follows in the next posts).
6. Put a telescope on a mount.
7. Balance the whole system with counterweights and moving of the telescope tube.
8. Enjoy the good tracking!

That’s short review of the German equatorial mount. More read:

• http://en.wikipedia.org/wiki/Equatorial_mount
• http://starizona.com/acb/basics/equip_mounts_gem.aspx
• http://science.howstuffworks.com/telescope5.htm

Image source: http://www.company7.com/vixen/mounts/counterweights.html

Thanks for reading!

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A lot of astrophotograpers decide to make a modification of their cameras. The reason is that filter in front of CMOS or CCS sensor blocks almost all the H-α part of spectrum due to balancing the colors for daylight photography. But this is not suitable for astrophotography because almost all the nebulas consist of the Hydrogen and this light is cutted off just some millimeters in front of the sensor. If we remove that filter then we get much better response of the red color.

Since the Canon Rebel is the most common camera used between enthusiastic astrophotographers I’ll try to suggest some good links of step-by-step tutorials which guide you thought the process.

1. Canon Digital Rebel (300D) Modification
   Good tutorial with sample images before and after modification. For Rebel (300D).
2. ash’s Modified Digital Rebel XT Page
   Very nice tutorial for modification of Rebel XT (350D). I have done modification of my Rebel XT with this guide and he survived the operation!
3. Canon Digital Rebel XSi (450D) Modification
   Good guide with pictures and everything well explained for Rebel XSi (450D).
4. Canon Digital Rebel (300D) Peltier Modification
   Guide how attach Peltier cooling element into Rebel. Works good for long-exposure astrophotography.
5. Another Digital Rebel XT (350D) Modification
   Just another Digital Rebel XT mod. Maybe someone finds it useful.

For the end I am presenting one of my images after the modification. The Veil Nebula, NGC 6992:

The Veil nebula (NGC 6992) @ Primož Cigler

equipment 300D, astrophotography, camera, canon, digital, filter, images, links, nebula, rebel, tutorial, veil

I still remember my beginnings in astrophotography some years ago. I joined some astrophotography forums and admired the pictures some masters were taking. I didn’t have a telescope, a mount or any other equipment. I had just a Canon 3000N camera and kit lens.

Many of you would say that with this equipment astrophotograhy is just impossible. But this is not true! I have spent a lot of time capturing the moon with my very first telescope (60/700 Meade) and the star trails. The pictures was often useless but I have learned a lot for my progress.

I have been searching a lot to find the first picture of star trails I managed to take but I haven’t found it. So I can show you the one I have made 2 months ago:

Star trails @ Primož Cigler

For image like this you don’t need any special equipment. Almost every digital or analog camera for daylight photography is ok. Everything that is obligatory is a stable tripod where we attach the camera and remote control for expositions is useful too.

Analog cameras are more suitable for this type of astrophotography because they don’t have a digital noise. Exposition can last as long as we want and that don’t influence on image quality. We just set the length of exposition (usually between 30min and 3 hours), the field of camera (usually to the widest) and start the exposition. We generally use low ISO speed for capturing star trails – ISO100, ISO200, ISO400, rarely more. The length of exposition, ISO speed and aperture depend from the conditions, especially from light pollution. The more light pollution we have, lower ISO speed we should use and take shorter exposition.

If we use digital camera the process is little different. As I mentioned the digital cameras have a digital noise which grows as the length of exposure. To avoid this problem we take a set of continuous shots one after another where single show is long from 1 to 3 minutes. It’s important that between exposures in no more than 5 s of pause and that we don’t move the camera all the time during the exposures. At the end we also make a dark-frame (we cover the lens of the camera with a cap and make the “dark picture” just the same length and with the same settings as all the other pictures before), which we be needed after at processing.
If we done everything ok then processing is just the easiest part. We just download this software called Startrails and combine all the pictures. That’s all!

I hope that this article/post will help someone to start with astrophotography. Star trail can be really beautiful, just give them a chance!

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