|
this page is a collection of handy tools, useful gadgets and helpful procedures which we came across during our astronomical imaging ventures. whether you are searching a specific information or stopped by accidentally, we would be pleased if you find something useful. |
|
paint it black
unwanted reflections inside a telescope or an accessory are a nuisance for visual observers as well as for astro imagers. the standard factory coatings of inner tube walls, eyepiece barrels, focuser tubes etc. often leave much to be desired. this is especially true for Newtonians, which are particularly susceptible to stray light entering the system. some observers try to cure their instruments with either blackboard paint or felt lining. both solutions have their drawbacks, as even matt-black blackboard paint still reflects a lot of light and felt tends to release lint which soils the optics. a better solution is the special light absorbing paint (Antireflexfarbe) produced and distributed by Astrogeraete Berger in Germany. the comparison below demonstrates how well the paint works. these are two images of the same focuser tube of a 110/440mm Skywatcher Newtonian against a bright light source. the left picture shows how much light is reflected by the inside of the barrel having the standard factory coating. the right picture shows the same barrel after its inside was painted twice with the special anti-reflection coating from Astrogeraete Berger. both images were shot under identical conditions. |
|
robotic imaging machine for free use
imagine: a 14" monster telescope riding on a top-of-the-notch Paramount ME equatorial, sitting in a dome on a mountain under the darkest sky you could possibly wish for. best of all, it is waiting for your personal astronomical imaging requests. sounds too good to be true? no! this is the Bradford Robotic Telescope, built and maintained by the University of Bradford, UK. the observatory is located on the Canary island Tenerife at an altitude of 2400m (7874 feet) on the Izaña mountain ridge. night after night the automated observatory opens its dome shutter to complete a huge batch of requests from all over the world. for setting up imaging requests the University of Bradford provides a nice web interface. completed imaging jobs are also available there for download. all you have to do is set up a (free) account which allows you to launch up to five requests at a time. once a job is finished, you can immediately start another. don't let the low-quality images displayed at the observatoy's website irritate you, because most of them are unprocessed single frames. with a little patience and proper image processing quite astonishing results are possible. see for example our image of M51, the famous Whirlpool galaxy, shot with the BRT in 2009. |
|
position angle at the eyepiece
when viewing the heavens through the eyepiece of a telescope, one can get lost easily. where the heck is southeast in the field of view? does jupiter rotate from left to right or from right to left? which way does the tail of that comet point? and where can the elusive companion of this double star be expected? these are some of the questions that arise during many observing sessions, night after night. to solve this problem, we designed a position angle scale that can be printed on cardboard and placed between any 1.25-inch eyepiece and focuser. once oriented, it points out the celestial directions in the field of view, shows the position angle and even tells the rotational directions of planets. there are two scales available, one for direct views (e.g. through Newtonians) and one for mirror-reversed views (e.g. through refractors with star diagonals). the scales are available for free download (0.8MB PDF) for non-commercial personal use. |
|
the magic light pollution filter
light pollution is the astrophotographer's universal enemy. the best solution is to avoid it and travel to really dark observing sites, a solution that is not always feasible. to achieve an acceptable signal-to-noise ratio even from suburban areas, light pollution filters are a viable alternative. today's best filter for photographic applications is the IDAS LPS-P2, available from Hutech, California. the effects of the filter are described easily: the sky background turns from brownish to a neutral grey, exposure times can be doubled and light pollution gradients are diminished or eliminated altogether. the sample images of M27 below (100% crops) give an idea of how the filter works. the images were shot with a Baader modified EOS350D with a 50mm lens at f/5.6 just outside Vienna. the left column shows an unfiltered image with 3 minutes exposure, unprocessed and processed. the right column shows a LPS-P2 filtered image with 6 minutes exposure, unprocessed and processed. compare the processed results and you know why the LPS-P2 is the first choice of many astrophotographers. our image of the Scutum Star Cloud is another example demonstrating the filter's effect. |
|
software for planning images
simply grabbing the camera and making a shot may work for easy picture aficionados but for premium results thorough pre-session planning is essential. a great deal of image planning is best made indoors using a desktop planetarium software. we prefer the open source program Stellarium, which is freeware and available for different platforms. the controls are game-like and pretty intuitive. various display options (e.g. atmosphere, light pollution, scintillation, etc.) produce an aesthetically pleasing preview of the real imaging situation. star catalogues down to magnitude 18 (NOMAD) are also available. Stellarium can be downloaded for free at www.stellarium.org. the screenshot below gives an impression of the highly realistic rendering of the nightsky. |
|
getting rid of the noise
a digital camera is a handy tool for shooting scenic nightscapes. but when using single-shot sources at higher ISO rates or with longer exposure times the results tend to become somewhat noisy. there is an easy cure! the software tool Neat Image is specifically designed to remove noise from digital camera images. it costs no fortune and a casual user will even find the free demo version sufficient. the software is available for download at www.neatimage.com. the demo version is fully functional except that the processed results can be saved in JPG format only. the sample images below (100% crops) demonstrate how well it works. download, denoise, enjoy... |
|
tool for limiting magnitude estimation
to find your night's naked eye limiting magnitude there is only one reliable way - the star count method of the International Meteor Organization (IMO). the method is simple, precise and easy to apply, but it has one major drawback: the documentation found on the web is practically useless for field work. that is why we generated our own modified map of star count fields. it is based on the original IMO fields, although we took the freedom of making some selections to increase usability. the map is a handy two-page document you can download (1.6MB PDF) for free for non-commercial personal use, print and take out into the field. clear skies! |
|
upper limit for deep sky subframe exposures
in our light polluted skies, deep sky subframes often cannot be exposed as long as desireable. experience tells that the sky background should not exceed one third of the camera's dynamic range. otherwise, too much detail gets washed out by the sky background and nothing is gained from the longer exposure time. to find the applicable exposure time, the visual naked eye limiting magnitude can be used. the graph below is based on testframes shot with a (Baader) modified Canon EOS 350D DSLR. it approximates the usable exposure time before the sky background reaches 33% of the camera's dynamic range. the graph is valid for 800ASA and f/4. use the correction table for your preferred ISO setting and your given f/stop. note that your personal graph may deviate a little, mainly because the naked eye limiting magnitude is a somewhat subjective matter.
|
|
photoshop toolset for astrophotography
yes, there is an astrophotography toolset even the casual photoshop user can work with. Noel Carboni's Astronomy Tools enrich Photoshop with about 30 one-click actions. the actions run fully automatically and bring out deep sky objects as well as faint stars, enhance contrast, reduce noise and blue halos, remove gradients and improve the overall look of an image. the experienced user benefits from the fact that each action can be applied from 1% to 100% and even to special selections only (e.g. stars).
the results of two of the available macros are shown below. the first picture is a crop of an unprocessed source, which is a stack of seventeen 120 second DSLR exposures of M31. the subs were shot under less than perfect conditions (limiting mag around 5.8), flats and darks have been applied. the second picture shows the result of the DSO-enhancement, while the third picture gives an impression of how well the macro for noise reduction works. all images are 100% to scale. in our opinion,
Noel Carboni's Astronomy Tools are the perfect software product: easy to install, fun to use, working flawlessly and best of all - pretty cheap, too. thank you, Noel. |
|
precision pointing for telephoto lenses
ever had a problem pointing a telephoto lens with high accuracy? then you know that the standard tripod head isn't the perfect solution for astronomical imaging. the Witty-1 is a small yet stable gadget that solves any pointing problems for equipment up to one or two kilograms. basically, it is a miniature alt-az mount allowing fine adjustments in azimuth and altitude. it screws directly between the photo tripod and camera/lens. the device even can be mounted on a telescope tube and serve as a convenient piggyback-mount. the Witty-1 is well manufactured, the knobs are large and the fine adjustments are smooth and reliable. for the cost of a quality ballhead it is a true bargain. the Witty-1 is sold by Baader Planetarium.
|
|
lunar eclipse imaging with short focus lenses
how much lunar eclipse do you get with a 135mm tele lens? the picture below gives the astonishing answer. it shows clearly that short focus standard lenses are capable of producing pretty nice images of partial or total lunar eclipses. for better resolution, we took 16 individual frames and stacked them with Registax. some further improvement with Photoshop was applied. |
