Day 10 Moon on 07 Nov 2008

[cataclysm]

Err... this image was the result of stacking 11 images (I thought I indicate it in my first post) and the stacking effect is there especially at the right side of the image. This "stacking" effect should be due to the atmospheric turbulence... the turbulence cause some part of the Moon to "shift" a bit in some of the images. As a result, some part of the Moon will not perfectly aligned even the rest of the Moon were aligned and cause the "stacking" effect when stacked.

Yes, atmospheric disturbance will affect large aperture optics more than small one.

[weixing]

Hi,
I reprocess the image again and post the reprocess image below the initial one to compare the different.

This time, I spend more time on cropping of the image accurately and use 2 point at each end (left and right) of the Moon for alignment. As a result, only 5 out of 11 images were accepted, but the result after the stacking is better:
1) The stacking effect on the right side of the Moon is minimize in the reprocess version.
2) There is one serious processing artifact appear in the full resolution image of the old version did not appear in the reprocess version (only visible in full resolution image).
3) The reprocess version was slightly sharper and clearer than the old version after stacking.

Have a nice day.

[Zephyrus]

The reprocessed version looks a lot better on the right side. The left side is also slightly sharper since the stacking effect is removed. Looks great! (:

[universe24]

That's good. The improvement is significant.

[pkhunter]

Hi weixing. This is stunning stuff. I have questions though.

(1) Where did you get the equipment? "Vixen R200SS" and the "2x barlow" -- did you rent them or do you own this pricey stuff?

(2) Can this stuff be rented in Singapore and used with a Nikon D200? I presume there are some adapters?

(3) What do you mean by "stacking". Does this mean you took 11 different slices of the image with your camera on tripod and then "stitched" them later using Photoshop or something? (Like we do with panorama) Or is "stacking" different from "stitching"?

Thanks!

[Airconvent]

Hi weixing. This is stunning stuff. I have questions though.

(1) Where did you get the equipment? "Vixen R200SS" and the "2x barlow" -- did you rent them or do you own this pricey stuff?

(2) Can this stuff be rented in Singapore and used with a Nikon D200? I presume there are some adapters?

(3) What do you mean by "stacking". Does this mean you took 11 different slices of the image with your camera on tripod and then "stitched" them later using Photoshop or something? (Like we do with panorama) Or is "stacking" different from "stitching"?

Thanks!

Hi pkhunter,
Welcome to Singastro! WX will be able to answer your questions better but since I am on the "midnight shift ha.ha", I'll try.

Yes, he owns all the stuff he uses. I guess his current configuration has been honed after years of buying and selling to find the exact one he needed.

Yes you can try and ask if anyone would rent their scopes to you but a better way will be to join an obs session and talk to the gurus first. Its not a cheap hobby but not that expensive either. You can try our vendors section to check out their equipment listing and prices as well as our second hand corner too.

Stacking is a means of using mathematical algorithms to extract image details from a sample of similar images. The more images, the better the result. Technically what the software does, I think , is average out the details over many samples to "best-guess" the missing parts required to increase the resolution/quality. For example, you get capture about 200 similar images of the moon but all with lower quality. By stacking them, the resultant image may be able to interpolate back some of the missing details. That's my layman explanation. WX will be able to explain it more technically

[weixing]

Hi,

(1) Where did you get the equipment? "Vixen R200SS" and the "2x barlow" -- did you rent them or do you own this pricey stuff?

Most of my current equipment were brought from fellow SingAstro members via the "Buy and Sell" section over the years, so not that expensive...

(2) Can this stuff be rented in Singapore and used with a Nikon D200? I presume there are some adapters?

Not sure whether is there any vendor provide renting services. Anyway, to connect your Nikon D200 DSLR to a telescope, you'll need a T-Ring for your Nikon D200 mount and an T-adapter. Check this thread for a visual example: http://www.singastro.org/viewtopic.php?t=5315

(3) What do you mean by "stacking". Does this mean you took 11 different slices of the image with your camera on tripod and then "stitched" them later using Photoshop or something? (Like we do with panorama) Or is "stacking" different from "stitching"?

"Stacking" is not "stitching". As what Airconvent explained, basically what "stacking" do is to increase the signal-to-noise ratio. The signal here means the image of the object and the noise is the random variation in a signal. The below are simplified process:
1) took a series of images on the same object.
2) alignment all the images so that all the common "feature" of the image are at the same position.
3) "stack" all the images-> "retain" all the common elements and reject all the uncommon elements.

Below are a simple example of "stacking". The "stacking" method use in this simple example is averaging all the elements and round to the nearest: 0 if < 0.5 and 1 if >= 0.5.
Object ---> 1 1 0 1 0 1

Image 1 -> 1 0 0 1 0 0
Image 2 -> 1 1 1 0 0 1
Image 3 -> 0 1 0 1 0 1
Image 4 -> 1 1 0 1 1 0
Image 5 -> 0 0 0 1 0 1
Image 6 -> 1 0 0 1 0 1
Image 7 -> 1 1 1 0 1 1
Image 8 -> 1 1 0 1 1 1
Image 9 -> 1 1 0 1 0 0

Result ----> 1 1 0 1 0 1

As you can see in the above simple example, all "images" are different from other images and different from the "object", but after the "stacking", the result is the same as the "object". OK... this doesn't happen in real world, but the result become better as the number of images we stack increase.

Anyway, we use "stacking" in Astrophotography basically because of
1) the object we want to image are usually very faint and we can't expose of such long time due to equipment or other limitation (sensor noise, tracking error & etc).
2) the "blurring" of the target cause by atmospheric turbulence.

Hope the above helps.

Have a nice day.