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A few people asked in the Comp discussion thread for last month how it was I was able to get an image of something 2.5 million light years away with an exposure of over 7 hours... well ... here, in brief, is how...
First off... the equipment...
In this shot... I have 2 scopes, mounted on my HEQ5 (tracking heavy duty tripod head. It's rated for 15Kg load, although you could put more on it, if you don't intend to use the motor drives)...
Scope 1 - The black scope... This is my imaging scope. A Celestron 80ED, 80mm aperture, 600mm, manually focussed, high grade, near APO refractor, it has a fixed focal ratio of f7.5. My 450d sits at the tail of it.
Scope 2 - The blue scope... This is my guide scope. A short tube 80mm aperture, 500mm, manually focused, achromat refractor. This has fitted to it, a Meade DSI1c which is used to mount control..
The DSI is connected to a laptop, which runs software that can be used to lock onto a star, and if that star moves, will correct the mount drives to put it precisely back in place. This allows me to take exposures, that are only limited in length by the sky glow. I've used 20 minutes, so there's no issues with the tracking at all.
The process.
Firstly, align the mount on polaris. Then align the scopes on the target, take some test shots for framing purposes. Then enable guiding, and get capturing... I used a series of 6 minute exposures (76 in total). These were taken over 3 seperate nights, and it's clear from the progression how the SNR improves with more frames (see below).. Then capture a series of flat frames, this removes vignetting and other oddities, like dirt on the sensor, dust along the optical train etc, but is dependant on camera orientation, so a new set must be taken if the camera or focus position is moved. I've found I get better results if I don't use dark and bias frames (they remove other things, but also, I've found some finer detail). Then all the frames are loaded into DSS and combined... it's a bit like merging to HDR. Then processed further in PS.
In total, in terms of total work involved in this image... from setup to completion of processing, allowing for setup and take down times on each session, stacking and editing... we're probably talking roughly 13 to 14 hours of work. But... it was worth it... Cos I can say... that's mine... I did it
I'm very happy with my result, and that's all that really matters in the end.
First nights worth of data, 17 frames
Then I added another nights worth of data, 31 frames (but I labelled it incorrectly)...
And the final nights worth, the end result and the image I entered in the competition (76 frames).
This is what the unprocessed image looks like, after stacking... The histogram, is pretty much all stacked up, almost in the black point.
Some facts about that object...
The Galaxy is about 2.5 million light years away, and spans 110,000 light years. There are billions of stars within it. It's about the same size and shape as our own milky way, but being mostly edge on to us, it's hard to see the spiral. It's hurtling towards us on a collision course at approx 500,000 kph, which means in about 3 billion years, Andromeda and our milky way will run through each other.
I hope that this helps explain what goes on, how, and what's involved.
First off... the equipment...
In this shot... I have 2 scopes, mounted on my HEQ5 (tracking heavy duty tripod head. It's rated for 15Kg load, although you could put more on it, if you don't intend to use the motor drives)...
Scope 1 - The black scope... This is my imaging scope. A Celestron 80ED, 80mm aperture, 600mm, manually focussed, high grade, near APO refractor, it has a fixed focal ratio of f7.5. My 450d sits at the tail of it.
Scope 2 - The blue scope... This is my guide scope. A short tube 80mm aperture, 500mm, manually focused, achromat refractor. This has fitted to it, a Meade DSI1c which is used to mount control..
The DSI is connected to a laptop, which runs software that can be used to lock onto a star, and if that star moves, will correct the mount drives to put it precisely back in place. This allows me to take exposures, that are only limited in length by the sky glow. I've used 20 minutes, so there's no issues with the tracking at all.
The process.
Firstly, align the mount on polaris. Then align the scopes on the target, take some test shots for framing purposes. Then enable guiding, and get capturing... I used a series of 6 minute exposures (76 in total). These were taken over 3 seperate nights, and it's clear from the progression how the SNR improves with more frames (see below).. Then capture a series of flat frames, this removes vignetting and other oddities, like dirt on the sensor, dust along the optical train etc, but is dependant on camera orientation, so a new set must be taken if the camera or focus position is moved. I've found I get better results if I don't use dark and bias frames (they remove other things, but also, I've found some finer detail). Then all the frames are loaded into DSS and combined... it's a bit like merging to HDR. Then processed further in PS.
In total, in terms of total work involved in this image... from setup to completion of processing, allowing for setup and take down times on each session, stacking and editing... we're probably talking roughly 13 to 14 hours of work. But... it was worth it... Cos I can say... that's mine... I did it
I'm very happy with my result, and that's all that really matters in the end.First nights worth of data, 17 frames
Then I added another nights worth of data, 31 frames (but I labelled it incorrectly)...
And the final nights worth, the end result and the image I entered in the competition (76 frames).
This is what the unprocessed image looks like, after stacking... The histogram, is pretty much all stacked up, almost in the black point.
Some facts about that object...
The Galaxy is about 2.5 million light years away, and spans 110,000 light years. There are billions of stars within it. It's about the same size and shape as our own milky way, but being mostly edge on to us, it's hard to see the spiral. It's hurtling towards us on a collision course at approx 500,000 kph, which means in about 3 billion years, Andromeda and our milky way will run through each other.
I hope that this helps explain what goes on, how, and what's involved.
John.
...
