Large Format Camera

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Photography have always been a passion of mine, ever since I got a Nikon 5700 camera in exchange for doing some coding about 10 years ago.

The heart of this camera is the TAOS TSL1412S sensor. This is a linear array sensor with 1x1536 pixels, each 63.5um square. By scanning the sensor in the focus plane I get a monochrome 4190x1536 image. The physical image size is 138x97mm. These numbers give non-square pixels, but that is easily adjusted in Photoshop.

I use an Arduino Due to A/D convert the image and an EasyDriver drives a stepper motor from ITeadStudio. A 2.2" TFT from Adafruit displays the light meter , settings and the image in progress. It also holds the SD-card.

I take full advantage of the 12 bit A/D in the Due. Using oversampling I can get 15 bits/pixel images.

The focuser is taken from an old film enlarger i found at second hand. I made the bellows myself.

It takes a while to scan the image. In daylight/sunlight I get an image in about two minutes (2ms shutter), but in twilight it takes about 45 minutes (200ms shutter).

I also added an adjusteable delay between each column. This way I can take an image over several hours, for example during sunset/sunrise.

Since a 10x100mm IR filter would probably be quite expensive I opted to skip it, giving near-IR images.

Connected: A Wifi module will hopefully allow me to store the pictures directly to an Android phone, avoiding SD-card latency and making it easier to use. By storing the pictures directly in the DCIM directory on the phone I can take advantage of the phone's connectivity and immediately upload them to the service of my choice.

Open: The source code for this project is released without any licence whatsoever. You are free to use it in any way you like. All drawings I made are published as well. But since most of the hardware is hand-built I don't have many of those. See the links on the left side of the page for source code and drawings.

And the Adafruit_ILI9340 library, slightly modified [ MIT licence, Written by Limor Fried/Ladyada for Adafruit Industries.]

First light! It took about two months to get to this point.

A macro image of some flowers during sunset. Image is scanned from right-to-left.

An image from a mountaintop near where I live.

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Blowing up the apple
jimmy.c.alzen • 08/20/2014 at 10:37 • 0 comments

Here is a higher resolution version of the apple picture from the video:
New focus screen is ready
jimmy.c.alzen • 08/18/2014 at 08:00 • 0 comments

The new focus screen is hinged in the bottom and a lot more solid than my earlier attempt.
Also it is adjustable, something I found out is necessary. The tolerance needed to get a good focus is a lot less than 1mm.
WiFi module
jimmy.c.alzen • 07/20/2014 at 13:58 • 0 comments

Success! WiFi module is working and connects to AP!
Running all three external devices on the same SPI bus caused some trouble. After a lot of debugging I found out that the CC3000 and the ILI9340 TFT uses different SPI modes, plus the CC3000 library uses an SPI interrupt. The quick-and-dirty fix was to add this to each driver function in Adafruit_ILI9340.cpp:
noInterrupts();
SPI.setDataMode(SPI_MODE0);
// function code
SPI.setDataMode(SPI_MODE1);
interrupts();
The elegant fix would be to take advantage of the SAM3X's enhanced SPI capabilities to select the correct mode and speed automatically when accessing different devices on the same bus, but then I would have to rewrite all three libraries.
Further developments
jimmy.c.alzen • 07/08/2014 at 18:26 • 0 comments

Two main things are in the pipeline right now:
1) Replace focus screen. The old one is way too flimsy. The new one will be made of glass. I have sanded a suitable glass plate, now it's just a matter of mounting it.
2) It would be nice with a larger display. That way I can see immediately if the picture is going to be any good and save time by cancelling it if it is not. I think WiFi+Android is the way to go here. I have ordered a CC3000 breakout board. Also I get to learn writing Android apps, something I wanted to try for a long time now. Maybe I can also get rid of the awful maximum latency on sd cards by storing the pictures on the phone (and letting Android buffer the data in RAM). Most writes takes milliseconds but once in a while it takes .5 seconds. That really is not acceptable when photographing something moving.
Apertures
jimmy.c.alzen • 07/04/2014 at 16:09 • 0 comments

So the camera is more or less finished. After using for a week or two I find I really miss a manual aperture stop. When using a 140mm F/3.2 from an old dia projector I can't set the shutter fast enough to avoid overexposing the images in daylight. This is because the Due can't A/D convert faster than about 300k samples/second without really complicating the code.
So this is what I came up with:
Why limit yourself to round holes when you can have some fancy shapes instead? Now I just have to find a way to make it quick and easy to change aperture stops.

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Discussions

OiD wrote 07/07/2014 at 20:59

It's a very elegant project. Congrats on getting it working smoothly!
I recently bought a Due and a 5" display and one of the thing I have wanted to build for a while is a scanning camera.
Why not use an external faster ADC? Or use sample and hold with multiple adcs?

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jimmy.c.alzen wrote 07/07/2014 at 21:08

Thanks!
That would certainly be possible, but I like to keep things simple wherever I can. It took only a few days to code up the arduino code using the built-in A/D.

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Jasmine Brackett wrote 07/07/2014 at 20:02

Hello Jimmy, your project has been featured over on http://hackaday.com/2014/07/07/thp-entry-a-digital-large-format-camera/.

I know you have just created the project, but it would be great if you could explain the 'connected' aspect of your project in more detail. It will really help the judges when they come to review it.

Your images are beautiful. Keep up the great work.

Are you sure? yes | no

jimmy.c.alzen wrote 07/08/2014 at 11:55

Well it isn't very connected, right now. Except maybe in a more abstract sense. This is the first project I have put up on the Internet, and the response has been fantastic! I feel a lot more connected now :) Thank you everyone for the feedback!

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dcgill wrote 07/07/2014 at 19:54

Have you any details on the cameras performance in starlight conditions? It may be a great place to start on a long exposure, wide field, star capture device if coupled to a tracking telescope mount.

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jimmy.c.alzen wrote 07/07/2014 at 21:09

Well it is a thing I have planned to try. The thing is, you dont need a tracking mount. You don't even have to move the sensor. I can just store image columns and let the sky rotate past the sensor.

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Large Format Camera

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