Astrophotography
What I can deep-sky objects photographed?
One of the aspects of deep-sky astrophotography that produces more confusion is to understand the apparent size that each object, not visible to the naked eye, as are some planets or the moon.
So I put an example which we hope will come to understand this: the relative apparent size of the moon and the great Andromeda Galaxy (also known as M31). The Moon has an angular size of about 31 arc minutes. M31 has an angular size of about 180×60 arc minutes.
In the picture, you can see a photo montage of the two in which you can see the apparent size relative . That is, if M31 had the same luminosity as the moon would look like in heaven. Impression is not it?
This object is immense and that despite its remoteness – 2.5 million light-years its apparent size is huge (in fact, twice the size of the Milky Way).
Implications From a photographic point of view
Deep Sky Photography – Implications From a photographic point of view
(A) In the case of emission and reflection nebulae, many of the best known, and photography have a very large angular size, so focus telescopes are used short to medium (between 200 mm and 1,000 mm overall ). In this case, the aperture (the diameter of the front lens) is very important due to the low luminosity of the object.
(B) The low luminosity of the object involves long exposures (about 3-5 minutes to 30-40 minutes) which has important implications for further processing (noise control) and the equipment used (it takes a ultra precise tracking sidereal to prevent the stars and the object exit calendar – trailing in English).
(C) light pollution (CL) is very important: it determines the contrast between the sky background and the object. The more CL, lower contrast and the worse the quality of the picture. The atmosphere on the other hand – these focus-has very little impact on the quality of the picture.
(D) In the case of objects of smaller apparent size, such as planetary nebulae and most of the galaxies, the approach changes: longer focal lengths are needed (not as much as Planet), the order of 1,500 mm to 3,000 mm. The opening is still very important (more open = more light = shorter exposure time). However, long exposures are kept, and the processing is similar to the large emission nebula.
Deep Sky Photography
In the picture of heaven profunfo, photographs are objects beyond our solar system, nebulae, star clusters, supernova remnants, etc .- and even outside the Milky Way, other galaxies.
The two essential features, from a photographic point of view, are its large angular size in some cases, more than 200 times the apparent size of a planet like Jupiter and small, sometimes very low-luminosity of the object, due to enormous distances that are now the scattering of light on a vast area of space.
In fact, the Deep Sky Photography we have a wide variety of cosmic objects, some with very large apparent sizes (in the case of some emission nebulae), those with extremely low luminosity (some dark nebulae), other with very small angular sizes (most planetary nebulae and distant galaxies, ie, almost all but half a dozen who are closest to ours).
Planetary Photography
The Photography Planetary , photographing objects found in our solar system and are characterized by an angular size (apparent size) very small: the best, planets like Jupiter, Mars or Venus, to the naked eye look like very bright stars. The second important feature is that they are very bright objects.
(A) Due to the small apparent size of the planets, telescopes are needed very long focal lengths, the order of several thousands of millimeters. Aperture (the diameter of the objective, ultimately, its luminosity) in this case is not so important.
(B) The second implication is that when bright objects are used relatively short exposures, the order of tenths of a second to few seconds.
(C) Another important aspect is that, due to the high magnification used, the degree of stability of the atmosphere (which is called seeing in English) is crucial to get sharp pictures. Turbulent atmosphere and result in high magnification blur and even distorted. Light pollution however, is immaterial.
(E) The small sensor cameras with small pixels are best, as to cover the angular field is very small, except in the case of the Moon. As an example, Jupiter has an angular size of less than one minute of arc while the moon has an angular size of more than 30 minutes, ie, more than thirty times the apparent size of Jupiter.
What is astrophotography?
Astronomical Photography (also known as Astro ) is usually divided into two camps: The Photography Planetary and Deep Sky Photography . In the first case, it is basically photograph the planets of our solar system, but also includes the satellites, including our own, and comets. In the second case, it is to photograph nebulae, galaxies and supernova remnants. The equipment needed for each case and the capture and processing techniques are quite different.
However, it should be noted that from our latitudes (Spain) there are few objects that are larger than 1 ° (a dozen or less). Some of the most photographed are:
• NGC 7000 (North America Nebula): 120 ‘x 120′
• M 42 (Orion Nebula): 65 ‘x 65′
• M 31 (The Great Andromeda Galaxy): 180 ‘x 60′
• NGC 1499 (California Nebula): 160 ‘x 160′
• M 33 (the Triangulum Galaxy): 68 ‘x 41′
• M 45 (Pleiades): 110 ‘
• NGC 6992 (Veil Nebula): 60 ‘x 60′
• NGC 6990 (Nebula Witch Head): 70 ‘x 70′
• NGC 2237 (The Rosetta): 80 ‘x 80′
• IC 434 (Horse Head): 60 ‘x 60′
In future articles we will comment on the equipment available for deep sky photography and the techniques and programs available for processing these types of photographs. I hope you have served as the starting point of an exciting-and difficult-fans.
Posted in Astrophotography | 
Tags: Astronomical Photography, astrophotography, Deep Sky Photography, Photography Planetary | 
No Comments »