I was curious why a large aperture on a lens reduces depth of field. To investigate this I set my camera up with a macro extension tube and a subject with lots of depth.
The subject is a potassium sodium tartrate (Rochelle salt) crystal mounted in a brass holder, with a copper contact wire for detecting the crystal's piezoelectric properties. From the perspective of the camera, this setup looks like this:
This image shows a very short field, as is typical with macro photos that are taken from very close to the lens. The focal plane is about 10 degrees off of perpendicular from the surface of the coins, and intersects the subject about where the copper wire wraps around the crystal.
To understand why some parts of the image created when the aperture is large are blurry, it's helpful to visualize the paths the light takes through the lens. I used this simulator to make a simple diagram:
From any given point on the subject on the left, light passes through every point on the lens and is focused onto the camera's sensor. If you imagine a tiny bug with an equally tiny camera walking around on the big lens and taking his own pictures of the subject, you would noticed that depending on where he was standing, his photos would each be slightly different, sometimes from a little higher or lower, or one side or the other. We can simulate the bug camera photos by taking a picture through a pinhole placed in front of the lens.
Because the tiny bug camera has a really tiny aperture, all his photos will have very large depth of field, they'll be sharp all over. My bug-simulator has a fairly large pinhole, you can see it near the top of the image, it's about 2mm wide, so I won't get as much depth of field, but you can definitely see that much more of the depth of the image is in focus, compare to the image above and note how in these both the rubber band near the back of the image and the reeds on the edge of the coin are sharp. Here the bug is walking from one side of the lens to the other:
It's hard to tell in the still images, but the perspective is different in each shot, the angles all change a bit as the bug walks across the lens. It's easier to see this if you user a bigger hole so that you get a full-frame image instead of the circular shot, but it's harder to see the increase in the depth of field. Here is another example with a slot to let in more light. Left side from the top of the lens, right side from the bottom.
Since the tiny bug camera can only collect a tiny bit of light with each photo, all those slightly-different photos will be quite dark. If we stack them all up to increase the brightness, we get the image we would get from the regular-sized camera. It's a bright, but only the parts that were all the same in the individual images will still look sharp in the combined image. The parts that were all slightly different will be all mixed together, making them appear blurry.
That's exactly what the big lens is doing, stacking together thousands of different perspectives of the view all taken at the same time. We could get deeper depth of field in the image by using a smaller aperture, but that makes the image darker. To compensate we can increase the light on the subject, leave the shutter open longer, or use a more sensitive sensor.
To really see this effect, it's best to see it in a video, so check this out:
OMG’s innaugeral FirLumber Rally was a great success, with 17 cars competing. Official results will be posted shortly, but in summary, Dave’s electric cheater was the fastest, Eric’s elephant was the most creative, and Nate’s car was the least effort to build. Additionally, Dan’s kids’ cars were the fastest among the Squares.
Members of OMG recently attended Maker Faire Kansas City. While hopeful that we’d be able to race our latest project “Barbie”–a souped-up power wheel–in the Power Racing Series, several set-backs caused us to withdraw from the event. Team OMGFTW (Omaha Maker Group for the win) may have been knocked out this time around, but we’ve already begun working out Barbie’s kinks, which means one thing–we’re already ahead of the game! Though we didn’t get to race, the Omaha World Herald wrote an article about the trials and tribulations of taking Barbie from a mere girly power wheel toy to a lean mean winning machine. We’re just a group of Racer tech wizards who drive a Barbie, but rely on a cowboy.
Tonight’s meeting was a great success, thanks in large part to Tom’s Balloon Animals presentation/workshop. Members and visitors were shown, and then guided through making a variety of plants, animals, and inanimate objects.
Additionally, we had a number of visitors, and worked on projects including a Peltier-cooler proof of concept and a grinder stand. We also dusted off an old Teletype, in preparation for it’s impending Twitterification.
Just a reminder, the Omaha Maker Group’s regular meeting on Tuesday, September 4th is an Omaha Creative Week Spark Event. We have several presentations on the docket, including a summary of the Omaha Maker Group (and Making as a whole), as well as a hands-on presentation on manipulating your car’s onboard computer for diagnostics and customization.
Hope to see everyone there! If you have questions, don’t hesitate to email firstname.lastname@example.org.
Would you like to learn about lock picking? Come to our meeting Tuesday July 10th @ 7pm.
The meeting will feature a talk from a member of Toool.us (The Open Organization of Lockpickers), Steve Beck.
Steve will cover three topics, two of which are a little more hands on-ish, the first will be a basic lockpicking talk, the second will be a re-keying talk with a demo and the third will be about making your own picks with a demo.
Stick around after the talk for socializing and Makery Shenanigans.
Somewhere, deep in the capital city of Nebraska, is a building. This building is full of smoke, full of mirrors. Inside, birds take flight, machinists grind away in a vast darkened wonderland, and countless scavenged items from around the countryside rest in hulking, sometimes dilapidated heaps, thrown into rows awaiting re-discovery and thrifty sale.
Need to romp in an old grain silo turned on its side? Do you want a 50s era dental xray machine for arcane experiments? Wait, is that a VW Thing? There’s an old jumbo-tron! Think of the possibilities. And oooh look! Fiberglass light fixtures the size of your mom! We could turn these into Death Star replicas! That’s a rather large magnifying glass over there and, ah… wait. Who really needs an Applebee’s sign?
That’s not really the point, people. Stop looking at that sign. This, friends, is the home of something much more special something you might need way more than an Applebee’s sign. The hackers and makers of Lincoln, NE lurk these grounds. They are Lincoln Makerspace, and select members of OMG had the pleasure of meeting them this past week.
This fine group of enterprising guys work out of an old window factory. They currently spend most of their time in a small office space on the second floor, where you can find various works of art, Maker style. There’s an automatic drawing machine, kinetic sculptures, a record player with an ember on top that creates a flaming vortex when lit, and a dapper CNC milled likeness of Einstein, to name a few things that decorate the space.
Beyond that, the picture gets more dirty, more crazy, more awesome. Their small office space is part of a huge building that has pretty much everything a maker would need to have an A team style warmachine creative fit. Professional machine shops aside, the old window factory and Lincoln Makerspace have a 20x10ft CNC to call their very own (incidentally, this is where Einstein came from). That would be impressive enough, were it not for this:
Gosh, what’s that? It looks like a 10ft tall robot arm, fully armed and operational. But what is it for? What…does it do?
Group member interests, when not flinging people around in racing chairs, include bioinformatics, physics, free energy, engines, robots, and art. So far Lincoln Makerspace is a small group, but they pack a big punch and have a very high cool projects to member ratio.
Omaha Maker Group is impressed. If you’d like to get to know the Lincoln Makerspace, you can reach them here. We look forward to working with this great group of guys in the future!
Following the success of the OMG Egg Drop contest, we’ll be hosting a Balsa Wood Bridge competition. Great for kids of all ages! Updates to follow. For now, you can get details on the competition rules on the forum, here: