Astrophotography

What Exactly Is Astrophotography?

Astrophotography is the photography or imaging of celestial objects, events, or areas of the night sky. It’s a fascinating blend of art and science that captures the beauty of the cosmos in stunning detail.

The Early Beginnings

Imagine peering into the heavens for the first time through a camera lens. The very first photograph of an astronomical object was taken in 1839, marking the dawn of astrophotography as we know it today. But it wasn’t until the late 19th century that advances in technology allowed for detailed stellar photography.

Technological Advancements

Modern astrophotography can image objects outside the visible spectrum of the human eye, such as dim stars, nebulae, and galaxies. This technique revolutionized professional astronomical research, recording hundreds of thousands of new stars and nebulae invisible to the naked eye.

The Role in Scientific Research

Astrophotography has an early role in sky surveys and star classification but has since used sophisticated image sensors and equipment, often for aesthetic purposes rather than scientific data. Amateurs use a range of special equipment and techniques to capture images that can be both beautiful and scientifically valuable.

Equipment and Techniques

Astronomical photography employs long exposures, with equipment and observatories often located in remote areas to minimize light pollution. Telescopes are rotated to follow the apparent motion of stars, and guiding is done through a second telescope called a ‘guide scope’ or via an automated system.

The Pioneers

The development of astrophotography as a scientific tool was pioneered in the mid-19th century by experimenters and amateur astronomers. Overcoming technological problems such as sagging telescopes and developing accurate clock drives were essential to capturing images of celestial objects.

Early Challenges

Early photographic processes had limitations, including slow exposure times and limited plate wetting time. The daguerreotype process was used to attempt astronomical photography in 1839, marking the first known attempt at this field. Tracking errors in guiding a telescope during a long exposure led to an indistinct fuzzy spot photograph of the Moon in 1840.

Breaking Barriers

The Sun’s solar corona was imaged during the Solar eclipse of July 28, 1851, by Dr. August Ludwig Busch and Johann Julius Friedrich Berkowski using a small telescope with an aperture of only 2.4 inches. More detailed studies of the Sun were made by Warren De la Rue starting in 1861.

First Star Photograph

The first photograph of a star other than the Sun was taken in 1850 by William Cranch Bond and John Adams Whipple using Harvard College Observatory’s 15-inch Great refractor. The English chemist William Allen Miller and Sir William Huggins used wet collodion plate process to obtain photographic spectrograms of stars, including Sirius and Capella, in 1863.

Advancements in the Late 19th Century

Astronomical photography became a serious research tool with the introduction of dry plate photography in the late 19th century. Henry Draper made a 51-minute exposure of the Orion Nebula in 1880 using photographically corrected refracting telescope. Andrew Ainslie Common used the dry plate process to record images of nebulae, including stars too faint to be seen by the human eye.

Large Telescopes and CCDs

The first all-sky photographic astrometry project was started in 1887, but it was never completed. The beginning of the 20th century saw the construction of large refracting and reflecting telescopes specifically designed for photographic imaging. 1m Hale Telescope and 48in Samuel Oschin telescope pushed film photography limits. Advances led to electronic imaging, replacing plates with more sensitive CCDs.

Modern Astrophotography

Telescopes now use large CCD mosaics for improved light sensitivity. Late 20th century saw giant multi-mirror telescopes and space-based Hubble Space Telescope advancements. Astrophotography is a popular hobby using various equipment and techniques.

Digital Imaging

Images are recorded on many media, including single-lens reflex cameras and digital cameras. Film exposure times range from seconds to over an hour, but are less popular due to lower costs and greater sensitivity of digital photography. Modern CMOS sensors offer higher quantum efficiency, lower thermal and read noise, and faster readout speeds than commercially available CCD sensors.

Image Processing

Both digital camera images and scanned film images are adjusted in image processing software to improve the image. Images can be brightened and manipulated to adjust color and increase contrast. Sophisticated techniques involve capturing multiple images to composite together, sharpening images, and filtering out light pollution.

Color and Brightness

Astronomical pictures show objects and phenomena in different colors and brightness, often as composite images. This is done to highlight features or reflect conditions, making the note of these conditions necessary.

The Equipment

Astrophotographic hardware varies widely among non-professional astronomers, ranging from general photographers to serious amateur astronomers collecting data for scientific research. Equipment must be portable to avoid urban light pollution, and cameras may use special filters and advanced processing techniques to reduce ambient light in the background.

Camera Modifications

Some camera manufacturers modify their products for astrophotography, while others offer specialized equipment designed specifically for amateur astrophotography. These cameras often allow sensor cooling, raw image readout, and computer control for automated imaging.

Types of Setups

Fixed or tripod-based setups are the most basic types of astronomical photographs, but other equipment setups include using webcams to record images or videos, and manually tracking objects over long exposures in a wide range of weather conditions. Foreground objects or landscapes are sometimes composed in the shot.

Objects Imaged

Objects imaged are constellations, interesting planetary configurations, meteors, and bright comets. Exposure times must be short to avoid star trailing due to the Earth’s rotation.

The 500 Rule

The 500 rule is used to determine maximum exposure time: Maximum exposure time = 500/Focal length in mm × Crop factor. Star trails are an artistic technique where stars become elongated lines in exposures lasting several minutes or hours.

Telescope Mounts

Telescope mounts with compensating gears for the Earth’s rotation include commercial equatorial mounts and homemade devices like barn door trackers. Single axis mounts, also known as star trackers, compensate only for right ascension, while dual axis mounts use two motors to drive both axes, allowing for longer exposure times.

Piggyback Photography

‘Piggyback’ photography involves mounting a camera/lens on an equatorially mounted astronomical telescope, using the telescope’s guide scope to center the field of view. Telescope focal plane photography uses the telescope itself as the ‘lens,’ collecting light for the camera. This method is difficult due to centering and focusing challenges.

Camera Attachments

Camera attachments to telescopes include prime focus (direct image on film/CCD), positive projection (telescope eyepiece or positive lens projecting an image onto film/CCD). Negative projection – This method, like positive projection, produces a magnified image. A negative lens, usually a Barlow or a photographic teleconverter, is placed in the light cone before the focal plane of the telescope objective.

Compression

Compression uses a positive lens (also called a focal reducer), placed in the converging cone of light before the focal plane of the telescope objective, to reduce overall image magnification. Afocal photography uses both the camera lens and the telescope eyepiece, allowing parallel light path when focused at infinity.

Filters

Filters are categorized into broadband and narrowband filters. Broadband filters allow a wide range of wavelengths to pass through, removing small amounts of light pollution. Narrowband filters only allow light from very specific wavelengths to pass through.

Remote Telescopes

Remote telescopes allow amateur astronomers to control telescopes far away in dark locations using computer-controlled mounts and CCD cameras. The digital data collected by the telescope is then transmitted and displayed to the user via the Internet.

Conclusion

Astrophotography is a captivating journey into the cosmos, blending art and science. From its humble beginnings in 1839 to today’s sophisticated equipment and techniques, it continues to inspire both professionals and amateurs alike. Whether you’re capturing star trails or detailed nebulae, each image tells a story of the universe’s beauty and complexity.