Back in 1992, when the CCD cameras started to become popular among amateur astronomers, these sensors had to settle for a few millimeters thick and less than 100 thousand pixels, the most popular cameras, almost the only available, were the SBIG ST-4 and LINxx, now based in the tiny TC-211 Texas Instruments: 2.6 mm square and 192x165 pixels.
Legendary SBIG ST-4. Although obsolete as a camera to take pictures, is performing very good services as self-guided camera.
Over the last 15 years we have experienced an unstoppable progress in improving the CCD chips, starring the two brands of increased production: Kodak and Sony, benefiting from the huge market resulted in the production of digital cameras and video cameras.
astronomical users should give thanks to the large existing market surveillance cameras and industrial and professional video cameras triple CCD, which use sensors in black and white, have helped maintain a continuous supply of such monochrome chips as necessary in the photometry, preventing us from flooding the CCD's in color.
Size comparison between different models of chips from Texas Instruments, Tektronix and Kodak, at actual size and enlarged to scale.
Thus, there has been an improvement in resolution by increasing the number of pixels of the sensors (and a decrease in their size), and field of view, thanks to increased area, so as it did in professional astronomy in the amateur Finally we remove from use the chemical emulsion, with all its drawbacks, once that could be achieved to some extent emulate their resolution and large field, adding the immediacy, the linear response and high sensitivity of the digital detector.
Comparison between three models of Sony CCD chip: ICX-249 (green) vs. ICX285AL (yellow) vs ICX493AQA (blue) designated by the camera models that have been used.
When choosing a camera model the logical choice at first would be that the bigger the better chip. Taking over the image field can more easily find the items you want to photograph, the large diffuse nebulae can be recorded in one take without having to make mosaics, and we got to have more reference stars for astrometry and photometry images.
But this option does not have to be the best for all users, depending on the type of work who wish to pursue and the instruments they hold. The first thing you have to consider is the focal length to work and die size, with the considerations already stated in a previous post blog.
Second comes the factor of economic availability. There are high-end cameras and cameras of lower-middle range. The cameras are more expensive the larger the CCD sensor that are mounted, but there are also more expensive models CCD chips being smaller than other cameras in cheaper brands.
may seem contradictory, but is that there are CCD cameras and CCD cameras ... each brand designed a camera with a different electronic system and adds or subtracts extra features that may be crucial or not, depending on the needs of end users, all while using the same model of CCD chip.
I take the liberty to name brands, without going into invidious comparisons, each house manufacturer usually demonstrate their level of quality with the price of their products. It is an indisputable fact, though we may be paying a bit extra just to buy a brand.
is not the same a SBIG, Finger Lakes in performance or QSI a QHY, Starlight-Xpress or Atik. Maybe, depending on what you want to do, requiring a higher number of options, or perhaps a more affordable brand is good value for money and fully satisfy us. I remind the reader that I am a happy user of a QHY, so I moved a special interest beyond an objective comparison.
But back to the topic at hand. We may be an interested observer to make variable star photometry particularly weak, we have a good saddle that is accurate in pointing and allow self-guided. In this case can interest an SBIG ST-7, the CCD option without antiblooming. The antiblooming version is slightly cheaper, and indeed there are other brands that offer much more field cameras at the same price or less, but the ST-7 is especially appreciated for its high sensitivity and good performance in its version without antiblooming (s ie, without the system prevents leakage of electrons blooming or bright stars that saturate the response in the image and create a defect very ugly, but that is irrelevant to an image of photometric purpose, provided that this spill will not affect the star measure)
By contrast, another observer may require a generous field, for example to search for supernovae or asteroids, essential task that is sweeping large portions of sky in a short time, while you need to work with a good resolution, and therefore with a moderately long focal length or longer.
If the available budget, high budget, you can access the gems from the catalogs of the big firms, such as the SBIG STL-11000M, with the KAI-11000 M chip, a "beast "the size of a 35mm negative and 11 megapixels.
If the available budget, high budget, you can access the gems from the catalogs of the big firms, such as the SBIG STL-11000M, with the KAI-11000 M chip, a "beast "the size of a 35mm negative and 11 megapixels.
The "crown jewel", the SBIG STL-11000
chip Kodak KAI-11000M
If economic opportunities are more limited, and can dispense with some of the extra features of SBIG, you can find the same model of chip running on a brand Atik camera. Moreover, without reach 35mm size CCD, the Kodak KAF-8300 offers a much broader field than most cameras, with a size of 13x18 mm, but its price is really affordable for the kind of detector that is.
The cameras are incorporating QHY-9 and SBIG ST-8300 (with very good price in the U.S.). May or attain the degree of perfection of the higher-end cameras, but with an operation correcta pueden dar unos grandes resultados, renunciando a ventajas como la de utilizar un chip sin antiblooming.
De esta forma un posible usuario dedicado a la búsqueda de asteroides, supernovas, etc, podría incorporar una cámara que ofreciese gran campo, con menos coste, asumiendo que es perfectamente válida para detectar una supernova en una galaxia o un asteroide. No tiene que hacer una fotometría extremadamente precisa de una estrella, sino una detección fiable (siempre cuidándose de no cometer errores con rayos cósmicos o ruido).
Aun queda otro factor a tener en cuenta, the location of the observation. In urban settings it is perfectly possible to operate a CCD camera, but care must be taken with a camera that offers plenty of room, as if mounted on a short focal length telescope, the background of light pollution is strong. While this does not prevent the detection of stars, creates difficulties for a good flat field correction or flattening of the field. This affects imperfect preprocessing can lead to the existence of additional noise when doing photometry. F5 I work now and I feel quite this effect, with 20'x30 'to management, let alone without having a too large area detector.
As usual, it's best to go reaching compromise between field and focal ratio. At a high focal field, though small, may be better corrected by flat, and a shorter focal length this correction is complicated, more vignetting, but pointed Frame work more comfortably, and is available in each shot of more stars reference for astrometry or photometry.
In short, we should choose the camera that goes better with the optical system is to manage and can choose from a wide spectrum of makes and models to be better adapted available budget, left to the discretion of the user's decision whether to pay for a few extra features that offer the best and most expensive brands.
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