The Planets

The planets are one of the first targets for every beginner amateur astronomer. Indeed, we get to see our own every day, but five others, Mercury, Venus, Mars, Jupiter and Saturn, could be easily seen with naked eye. Technically, Uranus could be also seen with naked eyes, since it’s just below 6-th magnitude – the limiting magnitude for most of us. These are among the brightest objects on the sky, so they are not hard to find.

 twilight

Conjugations and sceneries of planets

Camera with regular focal length lens (~50 mm) mounted on a tripod can be used to capture the scenery plus some stars around the planet (see photo above). Also, such setup could be very handy during planet conjugations.

Close-up views

If you want to see or capture more of the planet you’re looking at, you will need a telescope. Some additional magnification of your system is likely to be required. The different types of optical magnifications (Barlow lens, eyepiece, etc.) will be discussed separately. No matter what kind of optical system and detector you are using, you have to know how large your target would be on your images (in the focal plane). To calculate planet’s size in your detector use this simple equation:

d = a x F / 206,265

where d is the resultant size of the planet in mm, a is the angular diameter of the planet in arc sec and F the effective focal length of your optical system in mm. You can find the current angular size of the target planet in an almanac, online or using some planetarium software.

Equipment

mars
Mars

Getting an image of a planet through a telescope, especially when using some sort of optical magnification, could be tricky. For a start, you will need a decent size telescope, at least 6″ (150 mm), and a sturdy motor driven mount. Not that it’s impossible to use a telescope with a diameter less than 6″ (see my Saturn example below). If that’s what you have go for it; you could definitely get some decent images. However, some of the nice details would be lost due to poor resolution. In addition, your system would lack light collecting power, thus requiring longer exposure times leading to fuzzier images (lost details), because of turbulence, vibrations, etc.

Jupiter
Jupiter

After you have settled on an optical system, decide what kind of detector you will use. You have three general choices here – CCD, web or a regular camera. The best results could be achieved by web camera and stacking software. More on that latter. If you don’t have one, use what you already have. There will be a separate page discussing in greater details these three detectors. Here, I’ll just give you a brief overview.

  1. CCD cameras. With such cameras you would need to get at least three frames in different filters to get a color image.
  2. Web cameras. They have proven themselves to be the best choice for planetary photography for amateurs. Granted, you would need software to process and “stack” your frames to get an image, but it’s definitely worth it.
  3. Regular cameras. These could be two types:
  • Film cameras. Depending on your magnification and therefore required exposure time, stick within the 100-400 ISO range. For all my photos I seldom had to take exposures more than 10 sec. The shorter your exposure time, the better.
  • Digital cameras. The ISO range is similar to the film cameras, but please do experiment to find what would fit you best. Digital cameras do a better job in “collecting” photons.

The following images of Saturn were taken with different telescopes. Also, one was taken with a film, and the other with a digital camera. See the following section for more details.

saturn_digital

Other essentials that you may need to have can be found on my Observing tips post.

About the photos on this page

Top. This is a photo of the twilight plus Venus, taken with a 50 mm lens and a film camera (ISO 200), several seconds exposure time.

Mars. Taken with a Celestron C8, D = 203 mm, effective focal length F ~ 10,000 mm, film camera, ISO 200, 5 sec exposure time.

Jupiter. Taken with a Maksutov-Cassegrain telescope D = 150 mm, effective focal length F ~ 22,500 mm, ISO 100, 6 sec exposure time.

Saturn left. Taken with a Maksutov-Cassegrain telescope D = 150 mm, effective focal length F ~ 22,500 mm, ISO 100, 12 sec exposure time.

Saturn right. Taken with D = 63 mm (less than 2.5 inches!!!), F = 840 mm, digital point-and-shoot camera (but a decent one) attached after the eyepiece. Effective focal length F ~ 2,000 mm, exposure time 1/13 sec, ISO 100. Keep in mind that the crop factor would be very different from a regular film camera or even a DSLR.

Digital vs. film cameras

My Saturn experiments (see pictures above) are in favor of the digital cameras. As you can see, with proper settings you could get better images with a 2.5″ (2.48″ if we have to be precise) telescope than a 6″ one. You should realize that the actual resultant size, in mm, of the planet in the focal plane of my system is much larger in the film camera setup. However, the biggest problem is the longer exposure time of 12 sec (vs. 1/13 sec in the digital setup). This allows turbulence, vibrations and imperfection in the guiding system to blur the image, thus “robbing” it of its resolution.

As a conclusion, aim for exposures of no more than several seconds and play with your magnification system to get optimal, for your telescope, results.

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