Free f-stop timer?

[Barry S]

Thanks--this is great. I need to digest this, but some of us that haven't worked with an Arduino may need some remedial help.

 

[wiltw]

I am frankly puzzled.
I know what an f/stop is...the numerical value which represents the denominator in the ratio of the diameter of the aperture to the FL of the lens.
I know what a timer is.

How the heck do you TIME an f/stop?!?!?!

 

[Monito]

How the heck do you TIME an f/stop?!?!?!

The OP is speaking of his stops with reference to a base exposure. What he calls f/stops should probably be called simply "stops" so that they are divorced from apertures.

One stop more light is accomplished by twice as much time. Two stops more light requires four times as much time. Thus it is a power (exponential) function. Logs are the opposite of exponents.

Half a stop more light is had by multiplying time by 1.414 (the square root of 2), since you can take your base time, multiply by 1.414 to get a half stop more, and multiply that by 1.414 to get yet another half stop, a whole stop from the base time. By application of logarithms you can get any intermediate stop in terms of time from the base time.

 

[Nicholas Lindan]

How the heck do you TIME an f/stop?!?!?!

It's a very bad name for a timer.

The method got it's name before there were such things as f-stop timers. The method uses exposure times in seconds that follow the f-stop numbering sequence: 1.0, 1.4, 2.0, 2.8, 4.0, 5.6 seconds ... When used as times each is 1/2 a stop more exposure.

This timer and the Darkroom Automation system use decimal stops. 1.0 stops = 2.00 seconds; 1.5 stops = 2.83 seconds; 2.0 stops = 4.00 seconds ...

 

[polyglot]

It's a very bad name for a timer.

The method got it's name before there were such things as f-stop timers. The method uses exposure times in seconds that follow the f-stop numbering sequence: 1.0, 1.4, 2.0, 2.8, 4.0, 5.6 seconds ... When used as times each is 1/2 a stop more exposure.

This timer and the Darkroom Automation system use decimal stops. 1.0 stops = 2.00 seconds; 1.5 stops = 2.83 seconds; 2.0 stops = 4.00 seconds ...

Indeed. It should be called a logarithmic timer or similar. Here is an article on the method.

 

[Lee L]

The term 'f-stop timer/timing' probably comes from Gene Nocon, who described his method for printing in his 1987 book Photographic Printing, and I believe the timer his company produced (for a short time) was called an 'f-stop timer'. Those who followed on with similar concepts for enlarging timing kept Nocon's terminology.

Lee

 

[paul ron]

I too would be interested, especially if I didn't have to make my own PCB.

PCBs are available already built form Mouser....
Dead Link Removed

Also google Arduino and you will get hundreds of hits on projects n software.

 

[Lee L]

PCBs are available already built form Mouser....
Dead Link Removed

Also google Arduino and you will get hundreds of hits on projects n software.

I believe the PCB in question is to carry the timer project parts external to the Arduino, not the Arduino PCB.

Lee

 

[polyglot]

I believe the PCB in question is to carry the timer project parts external to the Arduino, not the Arduino PCB.

Lee

Yes. Arduinos are readily available for about $15-18 shipped; if I do a PCB it would probably be a "shield" that plugs into the top of an Arduino to handle the keypad, LCD and driver transistors for backlight and output relay. If one were mass-producing this they'd do it on a single PCB but for people putting this together at home, using a premade Arduino makes a lot of sense because it provides the power regulation and FTDI USB interface, the latter requiring SMD components. Not to mention that it would be quite difficult for an individual to even buy the components+PCB for an Arduino for the price they're sold at.

I've also simplified things a bit so that the external wiring is now trivial. An off-the-shelf solder-prototyping shield is quite sufficient to build this thing as long as it has at least 16 pins in a row to hold the LCD header (or just a 2x8 block if you want to use a ribbon) and most of them seem to. A custom PCB really isn't required at all, though the box-insides would look neater with it.

 

[ParkerSmithPhoto]

Very interested!

Could you please post a picture of your final design? I've read the project details, and being a DIY guy, I'd really like to make one of these.

 

[paul ron]

OK so where is the schematic and more tech details for this project?

Ya got me interested too?

 

[ParkerSmithPhoto]

Another question

What is the perforated board that everything is wired into? What would you suggest as a box to hold this?

 

[polyglot]

Check out (there was a url link here which no longer exists) for an update.