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LAN_403

HV Enthusiast

Sat Feb 11 2006, 09:37PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

For those with an interest in astronomy, here are some recent photos I've taken of several objects. If you have any photos of your own to share, post them here . . .

M31 - Andromeda Galaxy

NGC 891 Spiral Edge on Galaxy in Andromeda

Big and Little Dipper - NJ Pine Barrens

Famous Double Cluster in Perseus

Our beautiful star, the sun, setting at Coyle Field, NJ

uzzors2k

Sat Feb 11 2006, 10:42PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Wow! Those are great! What kind of telescope are you using?

Eric

Sat Feb 11 2006, 10:47PM

Registered Member #69 Joined: Thu Feb 09 2006, 07:42AM
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Posts: 116

Those shots are awesome. I had no idea you could get photos like that with amateur equipment. Did you retouch them? The one of Andromeda is very cool.

Michael W.

Sat Feb 11 2006, 10:54PM

Registered Member #50 Joined: Thu Feb 09 2006, 04:07AM
Location: Vernon, B.C, Canada
Posts: 324

I've done some Lunar and planetary photography with my Digital Camera and my 4" reflector.

HV Enthusiast

Sat Feb 11 2006, 11:00PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Posts: 3068

These were taken with a 4" Takahashi refractor on a guided Losmandy GM-8 mount and with a Canon 20Da DSLR. The dipper shots was taken with a 15mm f/2.8 lense and the sun shot with a 200mm f/2.8L lense.

Here are three more of my favorite shots (taken last year) . . . However these were done with an older camera - Modified Canon 300D and a 3" Williams Optics refractor (M42 and Horsehead), so i really want to get out again this winter to retake the Orion Nebula and the Horsehead Nebula with the much better equipment i have now.

Orion Nebula M42

Horsehead Nebula

Trifid Nebula

Ring Nebula M57

1139698817 15 FT493 Astrophoto Horsehead

Eric

Sat Feb 11 2006, 11:55PM

Registered Member #69 Joined: Thu Feb 09 2006, 07:42AM
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Posts: 116

So were they retouched or is that natural color, etc.? I'm curious to see the 'raw' shots if they were retouched at all.

HV Enthusiast

Sun Feb 12 2006, 12:52AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
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Eric wrote ...

So were they retouched or is that natural color, etc.? I'm curious to see the 'raw' shots if they were retouched at all.

The color you see in these photos is real - no coloring is added to these shots. However, there is a considerable amount of post-processing required to bring out the detail and decrease noise of the images.

Firstly, multiple light and dark exposures are taken - and RAW files are used for this which are then converted to 16-bit LINEAR TIFF files. Dark exposures involve taking shots with the camera with the optical system closed so that just dark current exposes the sensor. These dark frames are average combined and a dark master is obtained. Each dark master is then subtracted from each light frame, thereby removing dark current noise of the camera.

Secondly, each calibrated light frame is then aligned and average combined into a single master frame. This single master frame, because it is still a LINEAR TIFF file will appear completely black.

Next comes standard image processing. Non-linear stretching (also called DDP processing) is performed on this frame to bring the details out of the lower end of the 16-bit image file and to stretch the pixels (again non-linearly) so that it looks like a real image to the eye. In this step, all the detail, and colors in the final images usually take shape. If gradients are present, then additional processing is used to remove the background sky gradient and keep the black sky uniform. Finally, standard curves, levels adjustments and sharpening (i.e. Lucy-Richardson deconvolution) is usually performed as required until the final image is prepared.

In all, i usually spend about an entire night shooting one image, and then spend anywhere from 2 hours to a week in processing an image.

I could post the RAW images, but since they are LINEAR 16-bit files, they would look completely black.

Hope this helps.
Dan

Eric

Sun Feb 12 2006, 01:20AM

Registered Member #69 Joined: Thu Feb 09 2006, 07:42AM
Location:
Posts: 116

So, if I understand correctly, the image that you get is only very slightly exposed, hence the need to remove the dark exposure. Very interesting process. Could you post a TIFF of the image after the dark exposure correction? I want to see what I can get in photoshop...

How long is each shot exposed for?

HV Enthusiast

Sun Feb 12 2006, 03:40AM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Eric wrote ...

So, if I understand correctly, the image that you get is only very slightly exposed, hence the need to remove the dark exposure. Very interesting process. Could you post a TIFF of the image after the dark exposure correction? I want to see what I can get in photoshop...

How long is each shot exposed for?

No, the images are actually exposed as much as a typical daytime image, except images that come directly out of digital cameras (RAW or JPG) are already stretched by the image processing in the camera and stretch the image information that looks like an "s" curve. Linear files are unstretched and exactly what the sensor records.

The TIFF images are about 40MB each, so they are not something i could easily post.

Shots vary in exposure usually from about 60 seconds to up to 30 minutes in length, although the majority are probably around 5 minutes each. I'll usually take about 3-4 hours worth of exposure on a single object.

Dan

Dr. Shark

Mon Feb 20 2006, 08:45PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

These are really impressive pictures, post some more if you have them at hand.

Could you give a ballpark figure how much $$$ it takes to get the equipment for taking this kind of pictures? I guess the off-the-shelf telescope from the supermarket wont cut it, but then a 4" refractor does not seem to be out of reach of an amateur either...

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