After about 30 years as a travel and nature photographer, Charles Krebs said he was “yearning to see something new and different.”

He remembered taking pictures with a Polaroid through a microscope when he was nine. So he picked up where he left off, only this time with a digital camera and a microscope found on eBay.

“It enabled me to see a lot of new and fascinating things that didn’t involve a lot of travel and carrying around and shipping lots of equipment all over the place,” Mr. Krebs said.

The first time he entered the Nikon Small World Photomicrography Competition in 2004, he placed sixth. The next year, he took top honors with an extended depth of field micrograph of a house fly. He has also placed in the Olympus Bioscapes competition.

“It shows you how complex and beautiful the world is even down to levels that we can’t experience with our normal senses,” said Mr. Krebs, 61. He has been so successful at his rediscovered hobby that this year he was invited to be one of Nikon’s four judges.

Ranking the top images based on originality, scientific content, technical proficiency and visual impact was no small task, even for a panel of judges with a range of artistic and scientific expertise. “I would challenge you to pick the top 10, come back in three days and pick the top 10 again,” Mr. Krebs said.

Since 1975, Nikon has been awarding annual prizes to scientists and enthusiasts who take pictures through a microscope. Popularly known as a maker of professional and consumer cameras, the company is also a major manufacturer of biological and industrial microscopes. It announced this year’s winning images on Thursday morning.

The pictures swim somewhere in the ether between art and science, and the vocabulary to describe them has yet to be coined.

While artists like Mr. Krebs have excelled in these contests, this year’s top prize went to a scientist from the Tallinn University of Technology in Estonia.

Heiti Paves has studied chicken embryo development, embryonic neurons and plants, all under a microscope. His first-place image, using confocal microscopy to document the anther of a tiny thale cress plant, was a byproduct of his research on motor proteins that move organelles in plant cells.

Besides being “nice-looking plant organs,” Dr. Paves wrote in an e-mail message, anthers were a good subject because “they do not move very fast … The picture of my dreams should bring out motility of living cell, like a sports photograph.”

So far, he said, no success.

Like many scientific discoveries, some of the most aesthetically pleasing images emerge by accident.

Bruno Vellutini of the University of São Paulo in Brazil said he was lucky to find the juvenile seastar in the plankton samples he collected while looking for sand dollar larvae for his master’s thesis last year. The serendipitous find earned him fifth place.

“Scientific images don’t need to be beautiful,” he said. “To take a good picture, you need patience to prepare light, make sure everything is clean. It takes a lot of effort to create a technically nice image.”

But, he said, taking beautiful pictures “makes research more fun.”

Arlene Wechezak, a retired cell biologist, won 10th place with a photomicrograph of algae and diatoms she found while walking to the beach from her house in Anacortes, Wash.

“When you look through microscope for as many years as I did, you miss it,” she said. “It’s like another pair of eyes that you don’t have.”

Dr. Wechezak, 66, said that her picture illustrates that even at a microscopic level, marine organisms depend on each other. She said she is driven “to see something for the first time that you’ve not seen or maybe nobody has seen. That’s the carrot in research.”

Pedro Barrios-Perez, of the Institute for Microstructural Sciences in Ottawa, took third prize with a failed attempt to develop a photoresist pattern on a semiconductor.

“These pictures are taken out of my interest in art,” Dr. Barrios-Perez said. “If I show it to my boss, he just says, ‘Throw the sample away.’ I thought that it looked like a face with a fire that was warming up my days.” He added that the particular result “cannot be reproduced — some of this stuff just happens.”

Not all of the winning images were created by scientists using expensive state-of-the-art equipment. Gerd A. Guenther, 51, an organic farmer from Düsseldorf, Germany, produces vegetables, potatoes and hay for horses. His stunning picture of a flower stem section of a spiny sow-thistle plant won second prize.

“I chose this object for the remarkable contrast between the red hats of the plant hairs and the green stem, in combination with the white hair stems,” Mr. Guenther said in an e-mail. “I chose dark-field illumination to underline the color contrast with a black background.”

Mr. Guenther said he also likes landscape and macro photography, but focuses on photomicrography “because I want to share the wonderful symmetries and the remarkable structures of nature with other people.”

He added that the only way to protect nature is “if you know the entire diversity in every little puddle.”

James Hayden, who manages the microscopy facility at the Wistar Institute in Philadelphia, said he is drawn to both photographic art and science. He added:

Most microscopists have a streak of artist in them. It’s hard not to. You’re looking at things through a microscope that most people don’t see. The nascent artist in you sort of peeks its head up.

When a former colleague sent him a section of an anglerfish ovary, he said, he came up with the idea of looking at the autofluorescence of the tissue in two colors. His vibrant swirling photomicrograph came in fourth.

Mr. Hayden also teaches scientific photography at the University of Sciences in Philadelphia. In addition to exposure, composition and lighting, he stresses the importance of treating pictures as scientific data. “If you don’t know what you’re doing, and don’t do it methodically,” he said, “the scientific results you’re trying to extract aren’t valid.”

And he talks about the ethics of Photoshop. He used Dr. Hwang Woo Suk, the South Korean researcher who fabricated evidence of human cloning, as an example of the unethical manipulation of scientific images.

When it comes to photo contests or cover art for a scientific journal, Mr. Hayden said, it’s often a matter of taking a boring lab image and finding new ways to photograph it to make it more visually interesting. “Good pictures act as ambassadors between scientists and the general public,” he said.

Havi Sarfaty of the Israel Veterinary Association won sixth place for her picture of discus fish scales magnified 20 times.

“From an artistic point of view, I think it’s beautiful,” Dr. Sarfaty said. “I even hang it on the wall in my house, printed very large: more than one meter square. It is beautiful but you don’t know what it is. When I put it on my wall, I don’t care what it is anymore.”