It's been a long time since I haven't built a contraption. Well, here is a really simple one that pretty much anyone with a soldering iron and very basic skills can do.
Like all inventions, it started with a problem. I have bought some Arista Lith 2.0 film to use in my Graflex. I know that it's not safe to use under the same safelight as regular photo paper, so I tried finding a red safelight at a low price but couldn't even find a single one in the entire metropolitan region!
So, I had to do a bit of research and decided to build one myself. It had to be easy to build, safe and mostly cheap.
So, I did a bit of research and looked-up the different material's spectral sensitivity. Here's what I came up with.
Spectral Safe ZonesMaterial
| Low frequency
| High frequency
|
Arista Litho 2.0
| 600 μm
| 750 μm
|
Ilford RC
| 575 μm
| 750 μm
|
Harman Direct Positive
| 650 μm
| 750 μm
|
So, all materials cut-off at 750 μm. That's a start. I also noticed that the Harman Direct Positive was the material with the highest base safe zone spectral sensitivity of the bunch, so I started there.
I first went looking at a local electronics superstore's website to see what existed. It's then I was struck when I saw a 660μm LED. Just what I needed... but not the 20$ shipping they asked for the part. I tried a local parts store but no luck. The clerk had never even heard of somebody asking for a LED by its specific color like that. So it was off to eBay. Around 3$ and a good month later, I got the part. So I was off to find the rest that I needed.
Not wanting to blow-up the LED, I took the specified specs and went to one of the many LED calculators online (I liked
http://led.linear1.org/1led.wiz)
I know it all looks complicated but in reality it isn't. The source voltage is the voltage your batteries generate. I used two AA cells, so at 1.5 volts each, I put in 3V.
The DC forward voltage is the voltage the LED can handle. In the case of mine, it was 2.2 volts. The DC forward current is the power the LED can handle. For mine it was 700 milliamp. That gave me a resistor value of 1.2 ohms. Knowing that a greater resistance will just slightly dim the LED while still protecting it, I took the nearest higher value I had.
I found a switch in a random parts drawer. I bought a battery holder, some circuit board. The circuit board was needed because the LED is of the surface mount variety. I needed something sturdy to attach it to and solder the wires without breaking it.
Everything is now just a question of connecting positive to positive and negative to negative with a switch and the resistor in between. I like putting the resistor on the positive side, but anywhere would work fine.
For the case, I went the super cheap way by using a travel soap bar case from the dollar store. You can't get a better enclosure for 0.50$
I drilled holes for the switch using a step drill bit (definitely get one if you plan on drilling plastics).
So, here is the result. It's fully portable and produces more light than my Ilford safelight.
Now, I'm off to see how good it is
