Cosmicar 12.5mm at f/1.4
Cosmicar 12.5mm at f/8
Friday, February 5, 2010
Adapting a Cosmicar 12.5mm f/1.4 c-mount lens to the GH1
The micro four thirds (and standard four thirds) camera format makes it possible to use old c-mount lenses with decent results. The lenses with shorter focal lengths will not cover the image sensor fully, but it seems that anything 25mm or longer will have full sensor coverage. These lenses are very cheap (eg $30), and the quality is surprisingly good.
This is the cosmicar 12.5mm f/1.4. I got it here:
http://www.surplusshed.com/pages/item/l10128.html
One problem is that the fast, short focal length lenses have a very wide barrel. In fact, it is too wide to fit into the micro four thirds -> c-mount adapter. I machined both the adapter and the lens so that they would fit together and also achieve infinity focus.
The lens has a brass mounting plate with the C-mount threads on it. It comes off very easily by removing the three screws around the periphery.
I used a lathe to cut an angle onto the edge of the brass mounting plate.
I cut the same angle onto the C-mount adapter. I bought mine from an eBay seller called rainbowimaging.
I'm pretty sure infinity focus has been achieved. If you think this image looks soft, it may just be the overall characteristic of the lens. It is $30.
The real benefit of theses lenses is that they are very fast (f/1.4) and wide, so they are ideal for indoor video. The 16:9 format works a little better with the image circle produced by the lens.
This has been very helpful in choosing lenses:
http://spreadsheets.google.com/pub?key=p9kkgjwEQQQ-HJwvNDobeEw
Also note that this is my second attempt in adapting the cosmicar to the camera. I had bought a c-mount adapter previously and machined it without machining the lens. I eventually machined away so much material (accidentally) that the adapter became too weak and broke immediately. I then realized that some material must be removed from both the lens and the adapter to make it work.
This is the cosmicar 12.5mm f/1.4. I got it here:http://www.surplusshed.com/pages/item/l10128.html
One problem is that the fast, short focal length lenses have a very wide barrel. In fact, it is too wide to fit into the micro four thirds -> c-mount adapter. I machined both the adapter and the lens so that they would fit together and also achieve infinity focus.
The lens has a brass mounting plate with the C-mount threads on it. It comes off very easily by removing the three screws around the periphery. 
I used a lathe to cut an angle onto the edge of the brass mounting plate.
I cut the same angle onto the C-mount adapter. I bought mine from an eBay seller called rainbowimaging. 
I'm pretty sure infinity focus has been achieved. If you think this image looks soft, it may just be the overall characteristic of the lens. It is $30.The real benefit of theses lenses is that they are very fast (f/1.4) and wide, so they are ideal for indoor video. The 16:9 format works a little better with the image circle produced by the lens.
This has been very helpful in choosing lenses:
http://spreadsheets.google.com/pub?key=p9kkgjwEQQQ-HJwvNDobeEw
Also note that this is my second attempt in adapting the cosmicar to the camera. I had bought a c-mount adapter previously and machined it without machining the lens. I eventually machined away so much material (accidentally) that the adapter became too weak and broke immediately. I then realized that some material must be removed from both the lens and the adapter to make it work.
Sunday, January 31, 2010
DIY heated computer mouse
I modified my standard, cheap Logitech optical mouse to include a small heating element. This really helps out on those cold nights when I am too cheap (or energy-conscious) to turn up the thermostat.
I opened the mouse, and located ground and +5V locations on the circuit board. I added two strings of 1/4w resistors that each have 4 10-ohm resistors in series. Each string is 40 ohms, so at 5V, this comes out to 5/40 = .125A or .625 W. The total heating power is 1.25 watt, and the total current (250mA) is well below the 500mA limit for each USB port.
I opened the mouse, and located ground and +5V locations on the circuit board. I added two strings of 1/4w resistors that each have 4 10-ohm resistors in series. Each string is 40 ohms, so at 5V, this comes out to 5/40 = .125A or .625 W. The total heating power is 1.25 watt, and the total current (250mA) is well below the 500mA limit for each USB port.
Wednesday, January 27, 2010
DIY Steadicam construction
A steadicam is a device that is built to reduce the camera shaking and rotation that is associated with hand-holding a video (or film) camera. Everyone has seen the Blair Witch style footage where the camera is bouncing around and being shaken to death by the person holding it. Even the most trained camera operators cannot hand-hold a camera and walk without the footage showing some shaking. The steadicam greatly reduces the amount of shaking and provides much smoother footage.
The name "Steadicam" is actually a trade-marked name thought up by the Tiffen company who invented the first one. However, like Xerox, the name steadicam has come to mean any camera stabilization device. A very popular model is the Tiffen Merlin Steadicam. It looks something like this:
This is a copy of the Merlin that I built from junk parts that I had lying around the shop. In this photo, it is shown holding my friend's HV20. The construction has been detailed in other places on the internet. Here are the best places to start looking
http://www.youtube.com/watch?v=4pLBUC-O1js
http://rafgodlewski.wordpress.com/2009/05/02/diysteadicam/
http://www.diycamera.com/stabiliser/index.html
The water bottle on the bottom of the stabilizer can be filled and emptied to adjust the amount of mass at the lowest point of the system. Ultimately, it may be best to replace the mass with metal (washers or similar), but the water is great for adjustment and testing. The gimbal joint is a Traxxas 4949 "half-shaft" for large RC cars. I have two radial ball bearings inside the handle -- these are similar to skateboard bearings in size and quality. The aluminum plate is 1/8" thick and I drilled it to accommodate different camera mount positions. The aluminum square tube is 1/8" thick 1"x1" with a slot cut lengthwise along the bottom for balance adjustment.
The curved piece of metal is a large sector from a lazy susan bearing (aluminum). The handle was made from 1" aluminum bar stock.
Areas for improvement:
Instead of drilling a bunch of holes in the top plate, it would be better to cut a series of horizontal slots. I found out that the side-to-side balance is critical and having a slot would allow much finer control than jumping to the next hole. The front-to-back balance can be adjusted via the slot in the aluminum square tube, so it will be fine to move from one horizontal slot to the next in the top plate as long as fine horizontal adjustment is attainable.
The friction of the bearings and gimbal must be as absolutely low as possible. The traxxas gimbal has 3mm pins, and the corresponding holes in the plastic gimbal parts are a little tight. I happened to have a reamer of just the right size to loosen the fit. In its original form, the tight-fitting pin will transfer too much motion to the camera. Likewise, the ball bearings in the handle must be super low-friction. Using sealed bearings will probably not work because the rubber seal will create too much friction. If I were building another steadicam, I would focus even more on getting a super low-friction bearing system.
I might try experimenting with making a longer balancing arm. If the lower mass hangs further below the pivot, less mass will be needed, and the longer pendulum will favor slower oscillations. It seems like win-win, but the device may be more difficult to carry and use.
Panning control should not be ignored. I found myself gripping the traxxas shaft with my finger tips to control the camera pan, and this worked pretty well. Adding a knurled wheel might be nice.
The name "Steadicam" is actually a trade-marked name thought up by the Tiffen company who invented the first one. However, like Xerox, the name steadicam has come to mean any camera stabilization device. A very popular model is the Tiffen Merlin Steadicam. It looks something like this:
This is a copy of the Merlin that I built from junk parts that I had lying around the shop. In this photo, it is shown holding my friend's HV20. The construction has been detailed in other places on the internet. Here are the best places to start lookinghttp://www.youtube.com/watch?v=4pLBUC-O1js
http://rafgodlewski.wordpress.com/2009/05/02/diysteadicam/
http://www.diycamera.com/stabiliser/index.html
The water bottle on the bottom of the stabilizer can be filled and emptied to adjust the amount of mass at the lowest point of the system. Ultimately, it may be best to replace the mass with metal (washers or similar), but the water is great for adjustment and testing. The gimbal joint is a Traxxas 4949 "half-shaft" for large RC cars. I have two radial ball bearings inside the handle -- these are similar to skateboard bearings in size and quality. The aluminum plate is 1/8" thick and I drilled it to accommodate different camera mount positions. The aluminum square tube is 1/8" thick 1"x1" with a slot cut lengthwise along the bottom for balance adjustment.The curved piece of metal is a large sector from a lazy susan bearing (aluminum). The handle was made from 1" aluminum bar stock.
Areas for improvement:
Instead of drilling a bunch of holes in the top plate, it would be better to cut a series of horizontal slots. I found out that the side-to-side balance is critical and having a slot would allow much finer control than jumping to the next hole. The front-to-back balance can be adjusted via the slot in the aluminum square tube, so it will be fine to move from one horizontal slot to the next in the top plate as long as fine horizontal adjustment is attainable.
The friction of the bearings and gimbal must be as absolutely low as possible. The traxxas gimbal has 3mm pins, and the corresponding holes in the plastic gimbal parts are a little tight. I happened to have a reamer of just the right size to loosen the fit. In its original form, the tight-fitting pin will transfer too much motion to the camera. Likewise, the ball bearings in the handle must be super low-friction. Using sealed bearings will probably not work because the rubber seal will create too much friction. If I were building another steadicam, I would focus even more on getting a super low-friction bearing system.
I might try experimenting with making a longer balancing arm. If the lower mass hangs further below the pivot, less mass will be needed, and the longer pendulum will favor slower oscillations. It seems like win-win, but the device may be more difficult to carry and use.
Panning control should not be ignored. I found myself gripping the traxxas shaft with my finger tips to control the camera pan, and this worked pretty well. Adding a knurled wheel might be nice.
Friday, December 25, 2009
Using my hacked espresso machine
I recently bought a Saeco Titan coffee grinder, and have been very pleased with the consistency and control of the grind size. I had to hack it (of course) to get the grind fine enough for espresso, but it's working, and it seems like a well-built machine.
For info on adjusting the grind size outside of the factory settings, see here:
http://www.ineedcoffee.com/07/hack-starbucks-grinder/
The Saeco Titan, Starbucks Barista, and Solis 166 are all the same machine. There are probably a few other rebranded models out there too.
A few years ago, I took a Krups "steam-powered" espresso machine and retrofitted it with a temperature control and air pump. The air pump pressurizes the air above the hot water in the heating tank, and the water is conveyed from the bottom of the tank to the group head. Thus, the air pressure will be the same as the water pressure. This differs from commercial espresso machines which use a water pump to move a specific volume of water through the coffee. The pressure is determined by the resistance the coffee poses to the set flow rate of water.
The temperature control was hacked from an old meat thermometer. It has a very basic proportional control. The air pump was salvaged from a 12V tire-inflator compressor. The large circuit board is a computer power supply that provides high current 12V to the compressor.
About 14g of coffee, finely ground and tamped down into the portafilter.
http://www.youtube.com/watch?v=WfhszeLt40k
I realize my shot is a little fast and pours out too violently. I'm still figuring out the ideal pressures and valve opening sequences for this machine. Since this is essentially a constant-pressure machine and commerical machines are constant flow-rate, there may always be some differences in how the coffee is made.
Lots of crema. This demitasse holds about 2 oz with additional headroom for the crema. It tastes great! I am very happy with the espresso that it makes. On cold days, I usually take a sip from the demitasse, then dump the rest into a large mug of hot water for an Americano.
For info on adjusting the grind size outside of the factory settings, see here:
http://www.ineedcoffee.com/07/hack-starbucks-grinder/
The Saeco Titan, Starbucks Barista, and Solis 166 are all the same machine. There are probably a few other rebranded models out there too.
A few years ago, I took a Krups "steam-powered" espresso machine and retrofitted it with a temperature control and air pump. The air pump pressurizes the air above the hot water in the heating tank, and the water is conveyed from the bottom of the tank to the group head. Thus, the air pressure will be the same as the water pressure. This differs from commercial espresso machines which use a water pump to move a specific volume of water through the coffee. The pressure is determined by the resistance the coffee poses to the set flow rate of water.
The temperature control was hacked from an old meat thermometer. It has a very basic proportional control. The air pump was salvaged from a 12V tire-inflator compressor. The large circuit board is a computer power supply that provides high current 12V to the compressor.
About 14g of coffee, finely ground and tamped down into the portafilter.http://www.youtube.com/watch?v=WfhszeLt40k
I realize my shot is a little fast and pours out too violently. I'm still figuring out the ideal pressures and valve opening sequences for this machine. Since this is essentially a constant-pressure machine and commerical machines are constant flow-rate, there may always be some differences in how the coffee is made.
Lots of crema. This demitasse holds about 2 oz with additional headroom for the crema. It tastes great! I am very happy with the espresso that it makes. On cold days, I usually take a sip from the demitasse, then dump the rest into a large mug of hot water for an Americano.
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