Well, January is well amoung us, and here in Wales, January is something of a double edged sword.
Yes,the sun sets comparatively early here, at around 4pm, but along with the early sunset, comes clouds, LOTS of clouds. Now if these clouds were beautifully dainty wispy affairs then this wouldn’t effect my erstwhile hobby of astrophotography. But no, these are grey, heavy thugs, choked FULL of moisture. Added to that, after a long trip across the Atlantic Ocean, these clouds see the lush greenery of the Welsh coast, like a driver sees a rest room after a 300 mile drive.
Suffice to say, there aren’t that many clear evening in Wales that are worth getting my camera out for. But yesterday was one of those evenings.
I own a Nikon D90 with 2 lenses. The standard 18-105mm lens and the slightly more powerful 70-300mm. I used the 18-105mm lens, when I want to take pictures of ‘regions of sky’ or constellations. The other one is employed when I want to take images of specific objects. I’d call myself an enthusiastic, ‘but poorly executing’ amateur…
Yesterday evening, Jupiter lay low in the eastern sky, by far the brightest ‘star’ currently in the night sky. With a suitable exposure, as well as capturing Jupiter you can also capture its larger satellites (moons), the ones Galileo spotted when he looked through the ‘first’ telescope in early 17th Century. Nice to see, that I’m on a technical par with a genius from 400 years ago!! 🙂
Manual focus is a MUST as the sensor in my camera spends an inordinate length of time trying and failing to focus on virtually nothing. Open the lens as wide as it will go, (F number as low as it will go) and “up” the ISO, so it captures more photons of light.
Your rig (camera and tripod) must also be stable. Any wobble or vibration will ruin the picture, so a timer delay or remote control to activate the shutter is a MUST. I normally employ the timer delay.
This is what I captured. Even with a 2 second exposure, you can see the items in the image are already starting to trail. The solution, to decrease the exposure time, and “up” the ISO again.
Long exposures are a slightly more complicated due mainly to 2 unrelated, but equally annoying things.
The first, and easier issue to deal with is ‘star trail’ Any exposure of longer than around 20 seconds starts to show ‘star trail’. This is where the stars in the image no longer appear as point of light, but as ‘trails’. This is fine when you want to capture star trails, but somewhat inconvenient when you don’t. This ‘trailing’ is caused by the Earth rotating on its axis, which is a good thing, as it helped make life of this planet possible, and is an aftermath of the formation of the Solar System. But no worries, there’s a way around it. To maintain stars as ‘points of light’, means taking shorter exposures, and ‘upping’ the ISO, or tracking the object. This is a simple rig, so i’ll start by trying the first option.
‘Upping’ the ISO means making the sensor inside the camera more sensitive to light, so you need a less time to capture the same amount of light. Unfortunately, this is where another problem comes in. Light Pollution! This is the ‘glow’ you see from a city. Unwanted light, streaming upwards into the night sky, rather than downwards towards the ground, where (council) planners intended. Its the scourge of astronomers and wastes millions of pounds a year.
With a bit of suitable adjustment, you can remove ‘some’ of the light pollution. Here are pictures of Orion and Taurus, and if you know where you’re looking you’ll see a faint fussy blob that is Comet Lovejoy.
For those that can’t spot it, i’ve shown its location and its (very rough) track for the next few days in the picture below.