Wednesday, January 13, 2016

Introduction to Astrophotography - Part I

Inside my dome observatory during an imaging run
Astrophotography is my photographic escape. As a professional sports photographer, I am paid to run around freezing athletes in split second moments in time. For the past three years, my relaxation has been astrophotography, the yang to my yin as I spend hours in my observatory during new moon weekends imaging celestial targets.

Since it is impossible to cover all aspects of astrophotography in one blog post , this will be a multi-part post. This is Part I, intended as a walk through of astrophotography that can be done cheaply and simply with basic photography gear. Subsequent posts will migrate to more equipment intensive imaging and some of the more detailed aspects of the process. How far you choose to take it is entirely up to you.


My first astro image, a shot of a full moon through a telescope with a 35mm film camera in 1980
A full lunar eclipse shot through a 400mm lens and a teleconverter with a DSLR in 2010.
The images above are examples of what can be easily accomplished with basic equipment, be it a telescope or long lens and an SLR camera, one film and one digital. Astrophotography does not have to be complicated or expensive. Most of us can drive an hour, get away from city light pollution, and take photos of bright objects like the moon simply by placing a cell phone camera on the eyepiece of a telescope.

DSLR image of the Andromeda Galaxy
Naturally, the quality of images will not be comparable to what is possible with more sophisticated gear but there’s a lot of astrophotography that can be accomplished with every day photography equipment. Beyond that, the sky is literally the limit depending on your interest and budget.


Star Trails
Photographing star trails is one way to engage in astrophotography with basic photography gear. All you need is a camera body capable of long exposures (Bulb mode); a wide angle lens; a tripod; and a moonless, clear night at a location free from as much light pollution as possible.

An intervalometer is well worth the investment but not essential. This device will automate the imaging process by allowing you to program shutter speeds, number of exposures, and exposure intervals. A new Nikon intervalometer is pricey - over $150. I've had great luck with the aftermarket version made by Phottix (new - $50).

Once the imaging sequence begins, an intervalometer does the rest in triggering all the exposures you'll need. All that’s left for you to do is replace the camera’s battery if and when needed.

For circular star trails, locate Polaris (the North Star) and compose the image with Polaris in the frame. All other stars will appear to revolve in a circle around Polaris.

Eiffel Tower star trails composite
I created my Eiffel Tower composite using a Nikon D600, a 15mm Sigma f 2.8 fisheye, a Phottix TR-90 Intervalometer, and a tripod. The star trails consist of twenty four 15-minute exposures ISO 1600, f2.8, layered together. The Eiffel Tower image was shot at f2.8, ISO 1600, and 1/40th second.

As an aside, I also shot some "flats", "darks", and "bias" frames that were included in the pre-Photoshop processing of images. I shoot these frames for all my astro images. The pre-Photoshop process is called "stacking" and it's accomplished in software designed to combine a number of astro images together, i.e., Nebulosity and Deep Sky Stacker. I'll delve into "darks", "flats", and "bias" frames in a later post but if you're anxious to see what these are just Google the terms and you'll find a wealth of information about them and how to shoot them.

Meteor Showers
The technique used to shoot star trails can also be used for capturing images of meteor showers. Because of the sporadic appearance of meteors, numerous exposures are necessary to capture enough light streaks in the sky. To create a meteor shower in one image, shoot as many images as you can, select the ones with light streaks, and then layer them together while brushing out everything but the light streaks.

Perseid meteor shower composite
My Perseid meteor shower composite was created with a Nikon D800E and a Nikon 17-35mm f2.8 lens piggybacked atop my Celestron SE 8 telescope to minimize blurry stars. Absent a motorized piggyback telescope, keep exposures to a maximum of 30 seconds. I used ISO 1600 at f2.8 with my intervalometer set to 60-second exposures every 3 minutes for 6 hours on two successive nights. I added a few longer exposures of the sky to capture the Milky Way. The foreground image was shot during the day and then converted to simulate night in Photoshop, adding a faux light painting effect.

The Milky Way Galaxy
The Milky Way is another astrophotography image that can be captured with basic photography gear. At a clear, dark site on a moonless night locate the Milky Way in the night sky. A quick search on the web should help you find it. The best views in the Northern Hemisphere are from February through September.

The Milky Way
Using a tripod mounted camera, start with ISO 3200, f2.8 and a 25-second exposure. Next, shoot several over and underexposed images that bracket this exposure. Images shot with a shutter speed in excess of 30 seconds will show some blurring in the stars but no worries.

Finally, layer your images one on top of the other. Brush out the poorly exposed portions from each image. Do the same for any blurry stars from the slow shutter speed images. Then, merge your layers and make final processing adjustments.

Part II - Imaging the Solar System

In Part II, I will take you to the another level, which I consider to be the next logical step in astrophotography - imaging the moon and planets. Stay tuned.


Alan Hanstein said...
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Alan Hanstein said...

Excellent primer - thanks!