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I have made this image to try to explain why image stacking is often necessary in astrophotography.
It shows two different exposures of the same area (around Alpha Delphini) cropped from the full frame.
You see the photos on the left, the upper one was 2.5 seconds exposure at ISO 3200 and the lower one was 40 seconds at the same sensitivity.
On the right are graphs of the brightness profile along the horizontal line through the brightest star (Alpha Del). I deliberately angled the photos so there are two fainter stars on the same line.
The graphs have 4 traces: one for each of the colour channels (RGB) and black would be the monochrome version (actually root sum of squares at each pixel).
The camera had 14 bits per channel, which means the (digitised) brightness in each colour at any pixel can only have values from 0 to 16383 (2 to the power 14 minus 1). So there is a limited range that can be represented and even for the short (2.5s) exposure the bright star is saturated: its peak would have gone above the maximum and so it is chopped off and set to 16383.
The lower part of every trace is for the background (sky) pixels and it is quite clear that even for the short exposure they are not zero. Furthermore the red trace is always higher than the green and blue ones, which is typical of pollution from street lamps.
On the longer exposure (lower photo) we can see that the background is really high, leaving little room between that and the maximum. Hence the reddish fogged photo and a smaller brightness range of stars can be discriminated.
So we have to keep individual exposures short enough to keep the background as near zero as possible and also to keep as many stars as possible from saturating.
When we do that though the level of the fainter stars is barely above that of the background and they tend to be lost in the fluctuations (noise) of the background.
Stacking helps (if the software does it right) by adding the pixels up in a memory area that allows a much greater range of brightness values before saturation.
When I started trying to do this, around 2001, there was nothing available that could cater for the large images from DSLR's, only for the much smaller images made by CCD cameras. So I started to write my own software, which I call GRIP (GR's Image Processor - I had worked in imaging software in the 1980's and 90's, which helped).
GRIP has an accumulator image in memory that has 32 bits per channel for every pixel, so brightnesses up to 2 to the power 32 can be represented before saturation would occur. (You would need to add more than 250000 14-bit exposures for any saturation to occur so, yes, it's overkill but convenient for programming.)
So if we accumulated 16 of the 2.5-second exposures the result would be similar to a 40-second exposure except that the profiles would not be chopped off at the top. The trick then is to read out the accumulator into a normal image through a look-up curve which takes the minimum of the background level down to true zero, stretches the contrast of the levels just above the background to make faint stars more visible, and takes the maximum actually occuring brightness (of the brightest star in the image, if none have saturated) to the maximum of the target image (which will have either 16 or 8 bits per channel).
NB: If intending to do photometry, to measure magnitudes of stars, the contrast must be kept linear. Also no stars involved in the measuring must have saturated.
(I have adapted this from a page of my own site, where there is more detail. See www.grelf.net/astro_exposure.html.)
First session of Focus Stacking using free download Combine ZP. Doesn't seem to work with RAW files, so shot this in jpeg. There is unpleasant fringing, some of which I've removed. I got better results from shooting in RAW and then converting to jpeg: very time consuming. Equipment: Nikon D300, Nikkor 50mm manual lens, manual extension tubes. Lighting: 1 LED torch. Considering the basic equipment used, I'm pleased with this first effort.
This is Oliver painstakingly stacking and unstacking his stacking toy, riht after he learned how to use it, at about 10 months.
I posed a question on the blog today, asking what you like to see in the "basics" chapters of quilt books. I'd love to know if you'd care to take the time to let me know! Blogged.
Focus stacked in Element 12 with plug-in.
using two images should have been 3 as mid ground is not sharp. Still its a economic way to get focus tacking in Photoshop Elements. using smart phone to control camera on low tripod. with out having to get on my knees I could adjust position of camera on tripod looking at phone screen.
The concept of stacking two twisted is also possible for hexagonal twists. This is one molecule.
Folder: Dirk Eisner
Kami
I also managed an almost head on stack of the Figure of Eighty Moth I found the other day. I liked the angle on this female of the species, reckon they would make great pets if they were the size of a cat :)
Hikers in Oregon and Washington like to stack rocks. Often it is just for fun while taking a break, but these stacks can serve a useful purpose too. In places where a not so obvious fork in the trail occurs or where an access point is difficult to spot an obvious man-made shape is a helpful visual cue.
Photo taken near Wahclella Falls in the Columbia River Gorge National Scenic Area (Oregon, USA).
I love my horse. This is Corocotta. He's a five, yes, FIVE year old Irish Sport Horse gelding. Bravest horse in the history of brave horses.
Fun novice level log stack. I believe this was one of Corey's favorites because what you don't see is himshooting off like a rocket bucking on the backside with his ears pricked the whole way!
A stack is a geological landform consisting of a steep and often vertical column or columns of rock in the sea near a coast, isolated by erosion. Stacks are formed through processes of coastal geomorphology, which are entirely natural. Time, wind, and water are the only factors involved in the formation of a stack. They are formed when part of a headland is eroded by hydraulic action, which is the force of the sea or water crashing against the rock. The force of the water weakens cracks in the headland, causing them to later collapse, forming free-standing stacks and even a small island. Without the constant presence of water, stacks also form when a natural arch collapses under gravity, due to sub-aerial processes like wind erosion. Stacks can provide important nesting locations for seabirds, and many are popular for rock climbing.
Stacks typically form in horizontally-bedded sedimentary or volcanic rocks, particularly on limestone cliffs. These rock types medium hardness means medium resistance to abrasive and attritive erosion. A more resistant layer may form a capstone. (Cliffs with weaker rock - such as clay - tend to slump and erode too quickly to form stacks, while harder rocks such as granite erode in different ways)
The formation process usually begins when the sea attacks small cracks in a headland and opens them. The cracks then gradually get larger and turn into a small cave. When the cave wears through the headland, an arch forms. Further erosion causes the arch to collapse, leaving the pillar of hard rock standing away from the coast - the stack. Eventually, erosion will cause the stack to collapse, leaving a stump. This stump usually forms a small rock island, low enough for a high tide to submerge.
Astrophotography is generally harder than regular photography... You've got light-pollution from cities, and miles and miles and miles of air between you and your subject, the subjects are usually incredibly dim, and they move across the sky. This means that for an astrophotographer, the most expensive piece of equipment may not be the telescope or camera... It may be the mount. The mount has to track smoothly and accurately across the sky for minutes or hours as the object moves across the sky.
Astrophotographers do have one very large advantage over regular photographers though... Anything outside our solar system really doesn't change much. You could take pictures of the ring nebula, wait a year, and take some more, and barring a nearby supernova, you'd never be able to tell which was which.
One common technique used by real astrophotographers is called stacking. They take a bunch of pictures of the same object, and stack them together to pull out details that are not clearly visible in any one picture. This means their mount doesn't have to be quite as accurate, since each picture is of a shorter duration. It also helps to get rid of problems inherent to digital cameras like hot pixels and cold pixels.
To play around with this idea, I took about 100 pictures of the moon (no telescope, just holding the camera). Then I fed them all into a program called registax and these were the results for 1, 2, 4, etc. images. This was just a very low-tech experiment but I think it shows the advantage, and also the diminishing returns on a per-image basis.
I have always liked this stack of cups in a local coffee shop. So tidy and neat - so unlike me, my home and my life! Opposites attract eh!
South Stack is famous as the location of one of Wales' most spectacular lighthouses, South Stack Lighthouse. It has a height of 41 metres (135 feet). It has a maximum area of 7 acres.
Until 1828 when an iron suspension bridge was built, the only means of crossing the deep water channel on to the island was in a basket which was suspended on a hemp cable. The suspension bridge was replaced in 1964, but by 1983 the bridge had to be closed to the public, due to safety reasons. A new aluminium bridge was built and the lighthouse was reopened for public visits in 1997. Thousands of people flock to the lighthouse every year, thanks to the continued public transport service from Holyhead's town centre.
There are over 400 stone steps down to the footbridge (and not, as local legend suggests, 365), and the descent and ascent provide an opportunity to see some of the 4,000 nesting birds that line the cliffs during the breeding season. The cliffs are part of the RSPB South Stack Cliffs bird reserve, based at Elin's Tower.
The Anglesey Coastal Path passes South Stack, as does the Cybi Circular Walk. The latter has long and short variants; the short walk is 4 miles long and takes around two hours to complete. Travelling from the Breakwater Country Park, other sites along the way are the North Stack Fog Signal station, Caer y Tŵr, Holyhead Mountain and Tŷ Mawr Hut Circles.
Two sets of six stacked blades, just as in the last top. Even these very light fabrics are making nice designs :)
Stacked Potatoes:
8-10 potatoes, heavy cream, garlic, parmesan cheese, salt, pepper. butter. Mix and place in cupcake pan. Bake for 50 min. Top with sour cream and bacon
Robert Stack was born in 1919 in Los Angeles, California. His parents divorced when he was a year old, and he was raised by his mother, Mary Elizabeth (née Wood). His father, James Langford Stack, a wealthy advertising agency owner, later remarried his mother, but died when Stack was 10. He spent his early childhood in Adria and Rome, becoming fluent in French and Italian at an early age, and did not learn English until returning to Los Angeles when he was seven. He took some drama courses at the University of Southern California, where he played on the polo team. Clark Gable and Spencer Tracy were family friends who often took him hunting and fishing. By the time he was 20, he had achieved minor fame as a sportsman. He was an avid polo player and shooter. His brother and he won the International Outboard Motor Championships, in Venice, Italy, and at age 16 he became a member of the All-American Skeet Team. He set two world records in skeet shooting and became national champion. He took drama courses at Bridgewater State University, a mid-size liberal arts school located 25 miles southeast of Boston. His deep voice and good looks attracted the attention of producers in Hollywood. During World War II, he served as an Aerial Gunnery Officer and gunnery instructor in the United States Navy. He was awarded the World War II Victory Medal, Asiatic-Pacific Campaign Medal, American Campaign Medal, Expert Rifle Ribbon and Expert Pistol Ribbon.
In his first film he played the character of Ted Drake in First Love (1939). In his first Western film he played Jim Holliday in Badlands of Dakota (1941). He appeared in Western films with: Richard Dix, Ann Rutherford, Broderick Crawford, Andy Devine, Jackie Cooper, Ralph Bellamy, Mickey Rooney, Wanda Hendrix, Robert Preston, Joan Taylor, Robert J. Wilke, John Doucette, Virginia Mayo, Ruth Roman, Raymond Burr, Leo Gordon. Some non-Western films he appeared in were: The Mortal Storm, The High and the Mighty, Good Morning Miss Dove, Airplane, Caddyshack II, Joe Versus the Volcano. His final film appearance was as The Gooch in Killer Bud (2001).
He made his first appearance on TV in an episode of Pulitzer Prize Playhouse (1951). He appeared as a guest on other shows, but not in any Westerns. He is mostly remembered for playing the part of Eliot Ness in The Untouchables (1959-1963). He was the voice of Stoat Muldoon in the animated series Butt-Ugly Martians (2001). He hosted/narrated the true crime series Unsolved Mysteries (1987-2002). For 30 episodes he was the voice of Bob the Narrator on Disney’s animated series Hercules (1980/81). He portrayed Captain Frank Murphy in the series Strike Force (1981/82), Captain Linc Evers in the series Most Wanted (1776/77) and former federal agent turned true-crime journalist Dan Farrell in the series The Name of the Game (1968-1971). His final work on TV was as the voice of Reynolds Penland in an episode of King of the Hill (2001).
The Piikani Nation of the Blackfoot Confederacy, which was known as the Peigan Nation before the 1990s, honored him by inducting him into their chieftainship in 1953 as Chief Crow Flag.
His film and TV career spanned 62 years, during which he made more than 40 films and made many appearances on TV. In 1957 he won the Golden Laurel Top Male Supporting Performance Award. In 1960 he won the Primetime Emmy Outstanding Performance by an Actor in a Series Award, and was also awarded a star on the Hollywood Walk of Fame for his work in motion pictures. In 1971, he was inducted into the National Skeet Shooting Association Hall of Fame. In 1981 he was inducted into the California Skeet Shooting Association Hall of Fame (inaugural class). In 1996 he was awarded a Golden Palm Star on the Palm Springs Walk of Stars. In 1999 he received the John F. Kennedy National Award. In 2000 he won the Golden Boot Award. In 2001 he won the Temecula Valley International Film Festival Lifetime Achievement Award. His autobiography, “Straight Shooting,” was published in 1979.
He said about his role in The Untouchables: “Well, I come from a military family. Whether it's the country or city, I never liked the bad guy. I never put my arms around John Gotti, Al Capone or Lucky Luciano. For me, very simply they were the bad guys. And when I did The Untouchables, I told them going in, ‘If you try apologizing for any of these crumb bums, get someone else to play the part.’.” He also said: “As a matter of national survival, we need to do the best we can to sponsor the good guys and to do something active about bringing down the bad guys.” In a 1998 interview with The Associated Press, he said: "Somebody once said, ‘You really think you're Eliot Ness.' No, I don't think I'm Ness, but I sure as hell know I'm not Al Capone.' "
He underwent radiation therapy for prostate cancer in October 2002 and died of heart failure on May 14, 2003 at the age of 84. He and his wife, Rosemarie, had been married for 47 years at the time of his death.
He was an actor who didn’t take life in Hollywood too seriously. He said: "It's all malarky; even the wonderful part is malarky”. In life, and in the business, he was a nice guy and a professional, who followed the advice Clark Cable gave him when he was first starting out: “You're gonna be one thing: A pro. Show up on time, know your lines. ... And if you ever become a thing called a celebrity - a word I hate - if you ever do, and you use that power to push people around, I'm gonna kick you right in the (expletive)."
Rubbermaid Stackable Recyclers make recycling easy! Three sizes can be stacked and interchanged to suit your sorting needs. The flip door makes unloading recyclables a breeze. Stickers allow you to label your bin so you can see if you are sorting glass, paper, plastic, etc. The hood snaps securely to the base so you can transport your recyclables to a facility if necessary.
For additional information please visit: www.rubbermaid.com/Category/Pages/ProductDetail.aspx?Prod...
My first attempt with focus stackiing. 10 macro shots of a Christmas cactus with various focal points.
Taken with tripod, macrolens and Raynox clamp.
You know, it must be something about this 18-25 age range that makes people want to stack things like this. This particular achievement was a collaborative effort between Monty and myself.
(1/7/07 16:56)
South Stack is famous as the location of one of Wales' most spectacular lighthouses, South Stack Lighthouse. It has a height of 41 metres (135 feet). It has a maximum area of 7 acres.
Until 1828 when an iron suspension bridge was built, the only means of crossing the deep water channel on to the island was in a basket which was suspended on a hemp cable. The suspension bridge was replaced in 1964, but by 1983 the bridge had to be closed to the public, due to safety reasons. A new aluminium bridge was built and the lighthouse was reopened for public visits in 1997. Thousands of people flock to the lighthouse every year, thanks to the continued public transport service from Holyhead's town centre.
There are over 400 stone steps down to the footbridge (and not, as local legend suggests, 365), and the descent and ascent provide an opportunity to see some of the 4,000 nesting birds that line the cliffs during the breeding season. The cliffs are part of the RSPB South Stack Cliffs bird reserve, based at Elin's Tower.
The Anglesey Coastal Path passes South Stack, as does the Cybi Circular Walk. The latter has long and short variants; the short walk is 4 miles long and takes around two hours to complete. Travelling from the Breakwater Country Park, other sites along the way are the North Stack Fog Signal station, Caer y Tŵr, Holyhead Mountain and Tŷ Mawr Hut Circles.
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Love-in-a-Mist
A focus stacked 9 image macro of the flower "Love-in-a-mist" ( Nigella damascena ) Taken with my standard "kit" lens with a simple 16mm Macro tube on my OM-D E-M5ii using focus bracketing, then stacked in PS to give an "impossible" depth of field.
Rubbermaid Stackable Recyclers make recycling easy! Three sizes can be stacked and interchanged to suit your sorting needs. The flip door makes unloading recyclables a breeze. Stickers allow you to label your bin so you can see if you are sorting glass, paper, plastic, etc. The hood snaps securely to the base so you can transport your recyclables to a facility if necessary.
For additional information please visit: www.rubbermaid.com/Category/Pages/ProductDetail.aspx?Prod...