Mersing wide field test image using Canon 450D

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weixing
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Mersing wide field test image using Canon 450D

Post by weixing »

Hi,
The below is the wide field image of the southern sky I took during last Saturday Mersing trip for testing my new Canon 450D. It was taken with the EF-S 18-55mm F3.5-F5.6 IS Kit lens @ 18mm F5.0. It was a combination of 10 x 20s exposure at ISO1600.
Image

Since I didn't bring my tracking mount, so I plan to take a series of short exposure images (to minimize star trails) on a fixed tripod and stack them to create an effective longer exposure. I program my remote control to took a set of 10 images @ 20s exposure first, but I forget to check the time. By the time I return, it was 10 minutes after the last shot. :P I quickly start to take another set of images, but the dew start to form on my lens. As a result, I only had 2 set of 10 images of 20s exposure with 10 minutes different between them.

Anyway, when I return to Singapore and try to process and stack the 20 images, the result was really odd. The centre portion of the image was ok, but at the outer portion of the image, the star got the "flying away" look. After some inspecting of the image, I realised that the star did not align correctly at the outer portion of the image. As a result, all stars at the outer portion appear as "double" or become elongated. I realised that I was looking at the effect of the wide angle lens distortion... it cause the star to "shift" at a non-constant distance at the outer portion of the image as the star move across the sky...especially there is around 10 minutes of gap between the 2 set of 10 images I took.

So I decided to just use the first set of images I took earlier to stack, as the sky was better. The result wasn't that good as the 10 images of 20s exposure is not enough to overcome the noise at ISO 1600.

By the way, the noise was lower than I expected at ISO1600 for Canon 450D. I think the result will be even better if I manage to take more shot or shoot at a lower ISO.

Have a nice day.
Yang Weixing
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Post by wucheeyiun »

hi weixing,
do you know which software removes star trail the best... :) [smilie=ahaaah.gif]
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Post by rcj »

nice composure. but how come the stars look all whitish?
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weixing
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Post by weixing »

nice composure. but how come the stars look all whitish?
Hi,
Ya ho... I didn't notice it... [smilie=embarrassed.gif]

I think I might accidentally saturate the colour when doing processing as this is a quick output without much thinking... hmm... ok... I'm lazy... ha ha ha :mrgreen: :mrgreen:

I'll reprocess it when got time and this time I'll make sure I'll retain as much colour as possible... still learn how to do it the right way.

Anyway, I'm still waiting for the image processing software to better support Canon 14-bit CR2 RAW format. Hope they'll release an upgrade soon.

Have a nice day.
Yang Weixing
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Post by cataclysm »

Hi, its beautiful Weixing!
but how come the stars look all whitish?
Shooting at 1600ISO may results in loosing out on dynamic range. Hence, the star colours may have reached saturation. Imo, its ok to push the camera to high ISO for dso, as for star clusters, lower ISO will preserve the star colours.
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Post by rcj »

suspected so. it is the same case for CCD imaging as well. Short exposures for yielding good star colours. Long exposures for faint nebulae or galactic arms.
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Post by Airconvent »

ooooh....new toy....and canon too...rich owner [smilie=cool.gif]
Nice image , weixing, but from the glow, its clearly shows Mersing sky is deteriorating due to city development...
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universe24
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Post by universe24 »

Yo, the sky really clear....haven't see such clear sky so long...
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