M20 Trifid Nebula

[weixing]

Hi,
Took this image on 27 May 2007 early morning in Tampines. The weather was good and sky was very clear. It's was a very beautiful and interesting looking nebula 2000 - 9000 light years (a light year is the distance light travel in a year) away in constellation Sagittarius.



Capture Info
Telescope: Celestron 8" F5 Newtonian
Camera: Canon 300D Prime Focus with Coma Corrector
Location: Tampines, Singapore
Image: 30 x 1.5 minute Images @ ISO800

Have a nice day.

[eyes]

[asterixsg]

you had been up all night

Wonderful. Thanks for sharing.

[weixing]

Originally Posted by asterixsg you had been up all night Wonderful. Thanks for sharing.

Hi,
Thanks. This is the initial processing result... didn't do much processing.

Have a nice day.

[wong1979]

Really fascinating to see something so far away. I have one question which I'm not able to find on the net. By looking at stars, are we actually looking back into history? Since the distance are measured in light years...

[weixing]

Originally Posted by wong1979 Really fascinating to see something so far away. I have one question which I'm not able to find on the net. By looking at stars, are we actually looking back into history? Since the distance are measured in light years...

Hi,
Yes. Light travel very fast... around 300,000km/s, but the universe is even a bigger place, so the light of the stars will took a long, long time to reach us. So if we look further into space, we are actually looking at the light emitted long ago by the stars. For example, the Sun is around 150 x 10^6 km from us, so the light of the Sun took around 8.3 minutes to reach us. If we look at the Sun at any one time, we are actually looking at the Sun 8.3 minutes ago. If someone switch off the Sun, we only know it 8.3 minutes later.

So some actually refer telescope as time machine... the further we look into space, the further we look into the past.

Have a nice day.

[etegration]

Originally Posted by weixing Hi, Yes. Light travel very fast... around 300,000km/s, but the universe is even a bigger place, so the light of the stars will took a long, long time to reach us. So if we look further into space, we are actually looking at the light emitted long ago by the stars. For example, the Sun is around 150 x 10^6 km from us, so the light of the Sun took around 8.3 minutes to reach us. If we look at the Sun at any one time, we are actually looking at the Sun 8.3 minutes ago. If someone switch off the Sun, we only know it 8.3 minutes later. So some actually refer telescope as time machine... the further we look into space, the further we look into the past. Have a nice day.

great explaination and great pics too!

[swordman]

Hi Weixing,

I'm don't know anything about astro photography

however just curious, why 30 x 1.5 minute Images?

how come you need to expose so long? 1.5mins? and 30 images?

[weixing]

Originally Posted by swordman Hi Weixing, I'm don't know anything about astro photography however just curious, why 30 x 1.5 minute Images? how come you need to expose so long? 1.5mins? and 30 images?

Hi,
Most astronomical objects are very dim... so dim that our eye can't see it without optical aid. So in order to capture the dim light, long exposure are required. But there are some problems that limits how long can we expose in Singapore. The main issue are below:
1) Light Pollution: Since I'm taking the image at the visible light range, light pollution will basically limit how long I can expose before all pixels become saturated and we had serious light pollution in Singapore.

2) Tracking error: The stars and objects in the sky moves due to earth rotation. Although I used a tracking mount which will compensate the earth rotation, but there'll always be some errors due to gears and etc which will cause some tracking errors. This basically will limit how long I can expose before star trails appear in my image. This problem can be solve if you use guiding which require more equipments and I don't have the $$...

Anyway, in order to avoid and minimize the problems above, astrophotographer will break up one long exposure image into smaller sub exposure image and combine (stacking) them together during post processing to get an equivalent of one long exposure. The advantage of this method is that noise will be further reduce after stacking and you'll just lost one short sub exposure image if anything bad happen during the exposure (eg. a plane fly across the field of view). The limitation of this method is which sub exposure must be long enough for the sensor to capture some light of the target.

By the way, 30 x 1.5 minutes mean 30 sub exposure of 1.5 minutes exposure each... equivalent of one 45 minutes exposure.

Hope my explanation is good enough.

Have a nice day.

[swordman]

Icic thanks weixing for the detailed explanation. but curious, how does it look for 1 pic of a 1.5min exposure?

[weixing]

Originally Posted by swordman Icic thanks weixing for the detailed explanation. but curious, how does it look for 1 pic of a 1.5min exposure?

Hi,
OK... here is it... A single 1.5 minute exposure of M20 Trifid Nebula at ISO800. The sky is not black due to the serious light pollution.


Directly converted from the RAW image, resize and save in JPEG format.

Have a nice day.

[AReality]

ehhh...
wat focal length u used?


.

[weixing]

Originally Posted by AReality ehhh... wat focal length u used? .

Hi,
1000mm focal length.

Have a nice day.

[redstone]

How did you manage to avoid star trails?

[weixing]

Originally Posted by redstone How did you manage to avoid star trails?

Hi,
I used an equatorial mount with a motor drive which will compensate the rotation of the Earth by rotating the scope at the same rate as the Earth rotation and with good polar alignment (aligning one axis of the equatorial mount to the Earth's rotational axis), I can get 1 to 2 minutes (and may be longer) of exposure without much star trails.

Have a nice day.

[waterlucky]

Originally Posted by weixing Hi, I used an equatorial mount with a motor drive which will compensate the rotation of the Earth by rotating the scope at the same rate as the Earth rotation and with good polar alignment (aligning one axis of the equatorial mount to the Earth's rotational axis), I can get 1 to 2 minutes (and may be longer) of exposure without much star trails. Have a nice day.

Hi..weixing.. Nice Astronomy shots! Pls post more...is good educational topic... do u visit science center telescope often? so i assume u live at a high floor cos' no obstruction to field of view...
btw if i want to shoot star trails... can u recommend appropriate exposure time & ISO? Tks...

[Reno]

Hi Weixing,

I am really impressed with your shots.

I have a few questions. May i know where you actually locate the direction of the star? Also, what is the cost to get a similar setup like yours? I am kind of interested. Thank you.

[weixing]

Originally Posted by waterlucky Hi..weixing.. Nice Astronomy shots! Pls post more...is good educational topic... do u visit science center telescope often? so i assume u live at a high floor cos' no obstruction to field of view... btw if i want to shoot star trails... can u recommend appropriate exposure time & ISO? Tks...

Hi,
I seldom visit the science center telescope... the area there is very light polluted especially on Friday night when they open to public, because that's the time the near by golf course flood the sky with light... And I don't live at high floor.... I set up at a near by field to took the image.

Anyway, I seldom shoot star trails, so can't tell you exactly what exact setting to used. But star trails photo usually use very long exposure... up to a few hours, because the stars will only move 15° per hour. If you want an arc of 15° of star trail, you need an exposure of one hour. Also, the star trails will be shorter near the pole and longer away from the pole at a given exposure time. A longer focal length lens will also give star trails at a shorter time.

Since star trails photo need long exposure, ISO 100 are usually use to reduce the amount of noise. But the problem in Singapore is light pollution, so a single long exposure is basically out of the question. One solution is to go the digital way, take multiple shorter exposure shot continuously and combine them together... this will give you a digital star trails. Using this method, you may be able to use a higher ISO to give a brighter star trails, but you need to shorter the exposure time to avoid over expose by the light pollution... just take more shot if you want a longer star trails. Anyway, experiment with different focal length, setting and exposure until you get your star trails the way you want it.

Just my S$0.02.

Happy imaging and have a nice day.

[weixing]

Originally Posted by Reno Hi Weixing, I am really impressed with your shots. I have a few questions. May i know where you actually locate the direction of the star? Also, what is the cost to get a similar setup like yours? I am kind of interested. Thank you.

I'm using a non-computerize mount, so I use a star chart to locate the object that I interested in.

The price will vary with the quality and brand of the equipment, so I can't really tell you how much you'll need. But you'll basically need the following:
1) A mount with tracking capability. This is basically a must for Astrophotography and an equatorial mount is usually a must. The mount is very importance and a good quality mount will give you a smooth and more accurate tracking. With good polar alignment, it'll enable you to take longer exposure image (without star trails) without guiding.

2) A telescope. Not a must as you can always use your telephoto lens (if you have one), but you'll need one if you want to take smaller objects as it need a longer focal length with a relative fast f-ratio. An Astrograph (a scope design for Astrophotography) is always prefer, but it's very expensive. So you can always use a visual scope (I'm using a low cost visual scope) and can still get decent result.

3) Patient and don't give up. I think one of the most importance factor in Astrophotography. The good news is... it's free! You need a lots of them if you are using those not so high quality equipment.

Anyway, most of my equipment are not branded (it got brand, but not from the top quality brand ) and I get most of them from the used market, so it is a lot cheaper. If you are interested in Astrophotography, you can visit the Singapore Astronomy Forums ( http://www.singastro.org )... There are quite a number of experts (I'm still learning) there and also a buy and sell section that you may be able to get some used equipment at quite good price.

Have a nice day.

[Reno]

Originally Posted by weixing I'm using a non-computerize mount, so I use a star chart to locate the object that I interested in. The price will vary with the quality and brand of the equipment, so I can't really tell you how much you'll need. But you'll basically need the following: 1) A mount with tracking capability. This is basically a must for Astrophotography and an equatorial mount is usually a must. The mount is very importance and a good quality mount will give you a smooth and more accurate tracking. With good polar alignment, it'll enable you to take longer exposure image (without star trails) without guiding. 2) A telescope. Not a must as you can always use your telephoto lens (if you have one), but you'll need one if you want to take smaller objects as it need a longer focal length with a relative fast f-ratio. An Astrograph (a scope design for Astrophotography) is always prefer, but it's very expensive. So you can always use a visual scope (I'm using a low cost visual scope) and can still get decent result. 3) Patient and don't give up. I think one of the most importance factor in Astrophotography. The good news is... it's free! You need a lots of them if you are using those not so high quality equipment. Anyway, most of my equipment are not branded (it got brand, but not from the top quality brand ) and I get most of them from the used market, so it is a lot cheaper. If you are interested in Astrophotography, you can visit the Singapore Astronomy Forums ( http://www.singastro.org )... There are quite a number of experts (I'm still learning) there and also a buy and sell section that you may be able to get some used equipment at quite good price. Have a nice day.

Thanks man...!!