|
No, we're not going to ask you to run 26.2 miles. How would you stay up
at night to image if you were tired out from pounding the pavement?
Instead, since you're so awake from not running all day, why not spend those
sleepless hours taking pictures of the universe. Visual observers hold a
Messier Marathon each spring to see if they can find all 110 Messier objects in
one night. Why not take it a step further and image all the Messier
objects in a night? Or pick some other class of objects and image those.
Or just pick objects of any type and see how many you can grab in an evening.
Speedy Imaging
Any glance at the image gallery of an astronomy magazine will show that many
imagers spend hours taking a picture of a single object. How can we image
quickly if it takes so long to capture a single target? First, long
exposures are done to capture faint detail and multiple exposures are done to
reduce noise. For fast imaging, we might not be interested in the best
possible picture, just a decent picture. For this we need a fast focal
ratio. This will allow the most detail to be captured, with the least
noise, in a given exposure. Most telescopes are in the f/6 to f/10 range,
which is pretty slow for imaging. Ideally, for fast imaging, a scope
faster than f/5 will be required. Some refractors go as fast as f/4 with a
focal reducer. Specialized astrographs like Takahashi's Epsilon series can
be as fast as f/2.8. SCTs can be converted to f/3.3 systems with a focal
reducer, or f/2 systems with a HyperStar lens.
Summer at High Latitudes: How to Image Quickly
In 2004, we traveled to the Table Mountain Star Party in Washington to
demonstrate the HyperStar imaging system. The HyperStar was used with a
14" SCT, converting the scope to an f/1.9 system. Coming from Arizona I
had forgotten how long it takes to get dark in July at 47°
latitude. We were not able to begin imaging until about 11PM. We
demonstrated the system but pointing the telescope to an object, taking a single
30-second exposure through each filter (red, green, and blue), then combined the
images after they were taken to display the image. We let visitors jump in
and gave then a quick lesson in capturing images and let them take the pictures.
We stopped for a while to watch and photograph an auroral display. We
crashed into our tent at 2AM, tired from driving and setting up. All told,
we spent less than two hours imaging, yet we managed to capture full-color and
very detailed images of 15 deep-sky objects, from the Pinwheel Galaxy to the
Veil Nebula. Above are 15 of those images.
With one-shot color CCD cameras, even less time
would be required to capture fast but good images of deep-sky objects.
Someone spending more time at the wheel and less time explaining the system to
onlookers, and someone who wasn't interrupted by the natural wonders of the sky,
could knock off dozens of objects in just a few hours.
Above: Aurora at the Table Mountain Star Party.
Photograph by Scott Tucker.
CCD Imaging Projects
|
