1) What is the colourful bit in the middle of the photo called?
2) How do you go about taking a shot like this? Obviously he was using a
400 2.8 is, but what is the other stuff (IDAS LPS filter. A stack of 16x2
min, 6x30s, 30x10s,)
On Sun, 8 Jul 2007 19:07:02 +0100, "Ali" <me@privacy.com> wrote:
>Came across this photo of space on Pbase and think that it's pretty cool:
>http://www.pbase.com/image/38855314
>
>So the question are:
>
>1) What is the colourful bit in the middle of the photo called?
It's the Great Nebula of Orion. The 3 patches of horizontal stars (the center
group of stars deeply embedded in the nebula) are seen by the naked-eye as
Orion's sword hanging from his belt. If you are in an area where the sky is dark
enough you will be able to see the center star of the sword as a fuzzy patch.
That's that large nebula in that image.
>
>2) How do you go about taking a shot like this? Obviously he was using a
>400 2.8 is, but what is the other stuff (IDAS LPS filter. A stack of 16x2
>min, 6x30s, 30x10s,)
IDAS LPS is a Light Pollution Filter used to filter out the most prevalent
frequencies emitted in urban lighting (sodium and mercury lamps that have narrow
wavelength bands that can be filtered out). This causes a sky-glow, ruining the
contrast of deep-sky objects.
A stack of 16x2min etc, means he took 16, 2-minute exposures. 6x30s means 6
exposures at 30 seconds each. Then using a process called image-stacking
combined all the image frames from each set to get the very dim subjects to
appear that bright. It's a way of getting longer exposures with any camera. Most
any P&S cameras can also be used to take exceptional astro-photos with resulting
shutter-speeds of many hours duration by using the same method that this person
used. People using the new CHDK firmware overlay for some of the Canon P&S
cameras will be able to obtain all-night-long shutter-speeds, unattended, by
using a simple intervalometer script and using image-stacking. Provided they
have the camera on a tracking-mount to follow the objects in the sky. Otherwise
they will just get a full night of star-trails.
> Came across this photo of space on Pbase and think that it's pretty cool:
> http://www.pbase.com/image/38855314
>
> So the question are:
>
> 1) What is the colourful bit in the middle of the photo called?
A nebula.
> 2) How do you go about taking a shot like this? Obviously he was using a
> 400 2.8 is, but what is the other stuff (IDAS LPS filter. A stack of 16x2
> min, 6x30s, 30x10s,)
He's taken multiple exposures: two 16 minute ones, six 30 second ones, etc
and then combined them. Presumably a single exposure was too dim and noisy.
To get a sharp image of the stars would also require some kind of
astronomical device such as used by telescopes which moves the camera to
follow the stars, otherwise all but the 10 second ones would end up as star
trails. In fact I would have thought that image must have been taken
through a telescope, but I'm no astronomer so I couldn't say for sure, but
with a 400mm lens I'd be surprised if you could get that close to a nebula
unless it was pretty enormous. Mind you it does seem to be a selective
enlargement of maybe a 1/4 of the frame going by the smallish size of the
"original" shot, so maybe it is possible to get that close when you combine
the crop factor of the DSLR and the actual cropping, as the result may be
the equivalent of a 1200-1600mm 35mm lens. I still surprised though.
Gordon Freeman wrote:
> "Ali" <me@privacy.com> wrote:
>
>> Came across this photo of space on Pbase and think that it's pretty cool:
>> http://www.pbase.com/image/38855314
>>
>> So the question are:
>>
>> 1) What is the colourful bit in the middle of the photo called?
>
> A nebula.
The Great Nebula in Orion, Messier 42 and 43.
>
>> 2) How do you go about taking a shot like this? Obviously he was using a
>> 400 2.8 is, but what is the other stuff (IDAS LPS filter. A stack of 16x2
>> min, 6x30s, 30x10s,)
>
> He's taken multiple exposures: two 16 minute ones, six 30 second ones, etc
> and then combined them. Presumably a single exposure was too dim and noisy.
16 two minute exposures. The short exposures are for the brighter
parts of the nebula which are probably overexposed in the
2-minute exposures.
> To get a sharp image of the stars would also require some kind of
> astronomical device such as used by telescopes which moves the camera to
> follow the stars, otherwise all but the 10 second ones would end up as star
> trails. In fact I would have thought that image must have been taken
> through a telescope, but I'm no astronomer so I couldn't say for sure, but
> with a 400mm lens I'd be surprised if you could get that close to a nebula
> unless it was pretty enormous. Mind you it does seem to be a selective
> enlargement of maybe a 1/4 of the frame going by the smallish size of the
> "original" shot, so maybe it is possible to get that close when you combine
> the crop factor of the DSLR and the actual cropping, as the result may be
> the equivalent of a 1200-1600mm 35mm lens. I still surprised though.
No, that is the full frame. Many objects in the sky are quite
large. The Orion Nebula is about 1 degree in diameter, or double
the diameter of the full moon.
Yes, a tracking mount was used. Click the next button for some other
photos if his, which are wonderful!
This image is full frame at 700 mm on a 10D of the same nebula: http://www.clarkvision.com/galleries...3.v12-800.html
and processed to give the more pastel colors seen visually
through a very large telescope. More processing details are
given.
You can also click the next and previous to see other astro images.
The short exposure technique solves several common problems:
1) tracking errors (throw out any frames with bad tracking),
2) limiting the exposure length reduces dark current contributions,
3) imaging from light polluted cities is possible: simple
add many frames where a single longer one would saturate.
Then add the images and subtract off the sky light pollution.
Photographing Space 
Linear Mode
