Building a Light Meter

Hello all!

 

I am in the process of buying a Hassey 501 kit. So, I need a

lightmeter. Now, being in my fourth year of undergraduate

engineering, I think begin to think that it can't be that hard and

maybe I could just build a spot meter.

 

Has anyone tried this? Or should I my sanity and just buy a spot

meter?

 

Ryan

Ryan

 

Of course you can and should design and build a spot meter.

 

I assume of course that you have the experience, financial backing

and manufacturing expertise of Pentax or Soligor.

 

Otherwise, you are out of your *&^*ing mind!

 

Jerry

Thats awesome. First, I see I even write a proper sentence.

 

Thanks for the response. I will go bug Mr. Ebay now!

 

Ryan

.........Ryan.......are you on crack?

Next, you can start grinding your own lenses, and coating your own film.

Ryan,

 

You are opening yourself up to a lot of grief! It will ulitmately be far cheaper to buy a second-hand Sekonic or similar.

There is a fine line between what is practical and what is possible.You probably would be better off buying a pre-designed,pre -built spot meter.

Building the meter is about 1/10th of the problem. Calibrating it is the other 9/10ths.<p>BTW, I just bought a rather scruffy looking Gossen Lunasix for £15 ($21 US), and it's perfectly accurate.<br>I leave you to draw your own conclusions.

"To try and fail is but to learn. To fail to try is to miss forever the joy of knowing what might have been."

 

Enjoy the best of both worlds. Buy a spot meter by all means, but don't give up on the homemade job!

 

Ed

Ah .. try both a used meter and making your own for grins.

 

Actually .. what you might want to do is experment with making an incident meter. Spot meters are much more difficult.

 

For grins try picking up a silicon photo cell, use a resistor to load it (that will make it pretty much linear). Then use a inexpensive digital meter to read the voltage from it. Calibarate it using the sunny 16 rule (f/16 shutter = 1/ISO in sunlight). And go from there. You should be able to get about 0.25 v in sunlight (any more than that and you are probably off the linear area .. load it more), and since even an inexpensive digital meter can read down to 0.001 V you should be able to go down to about EV 8 at ISO 100. So you will not get a lot of sensitivity using this method.

 

As long as you keep a high load on the cell it will behave pretty much linear over a 7 or 8 stop range .. and thus calibaration is easy.

 

But .. by all means check for a used light meter .. it will end up being much easier to use.

 

Ken

your fifth year of college, or first year as a practicing engineer, you will learn to leverage off the works of others which frees up your time and energies for new explorations of your own. as an engineering student, this is too trivial a design to spend any time on. you will also find it is the mechanicals that present the most challenges.

Ryan,

When I was less financial I built a Light meter that worked as an ambient and flash meter. I chose a very fast Photo diode that had a good daylight charactersitic. Used it in current mode and amplified it with an Op-Amp. For a Flash meter, I used an Integrating Op-amp and another comparator to trigger the integration. A bit mode signal conditioning and fed the signal to a logarithmic A to D converter to display the result. I calibrated it against a friends expensive commercial meter. I had a couple of ranges to cover low light and brighter conditions. My design worked extremely well, in fact it had some advantages: Fot one reason I designed it so that it would operate accurately with very short duration flash (down to less than 20uS at high levels) because I was experimenting with high speed photography. I have never seen a commercial meter that actually specifies exactly what performance it will give at these short exposures. My meter didnt have the convenience of an LCD display etc, but it did its basic job very well. As an engineering student this should be within your capability. It will take a lot of time and may not be any cheaper but one day you may work for Sekonic and build a

better mouse trap.

Max.

Long time since I graduated from engineering school. You can perhaps do it in two simple, cheap ways. Either use a photo cell and a voltmeter (like the old fashion GE meter), or make a Watston [sp?] Bridge like an ohmeter, except use a variable photo resistor. Better yet, what if you just attached a variable photo resistor to an existing multimeter and measured its resistivity for different lighting conditions and compared it to a manufactured light meter for calibration?

 

Either case should give you an incident/reflective light meter depending on your voltage gain. Perhaps with some experiment you can add a switch to flip between the two conditions.

 

Best of luck...

I had a friend with perfect pitch. He built a very simple ambient

light meter which was a multivibrator with a photoresistor in the

feeback network. By listening to the tone he could tell you what

the exposure should be.

 

He liked baroque music, so Zone V was 414 Hz.

If you want to make photographs, buy a light meter. If you want to do engineering, build a light meter. But the cheapest (and surprisinly effective) meter is printed on the inside the yellow box. Sometimes you still get it as a seperate piece of paper.

You mean you can buy them ready made now? Damn!

Ryan,

 

Some people just can't understand the joy and satisfaction of building your own projects. Why rebuild a '66 Galaxie 500XL when you can buy a new Honda Accord? Why build a tube amp when you can buy a whiz-bang Sony? Why build a hand crafted wooden porch swing when you can get a plastic one at Target? Why print your own photos when WalMart can do it? Most people are content being happy consumers.

 

I agree that you'd do well to pick up an Ebay meter so you can have a relieable "go to" meter, but don't be discouraged. If you want to build a meter just to save money, it's probably not worth it, but if you value the learning experience, go for it!

 

D.M. Elick

Well thanks for all the comments! Two extremes :)

 

Here is my plan of action: borrow friend's Gossen Lunasix (sits in his closest anyways). Then, this summer, build my own. Maybe not a spot meter, but that's the plan. So you may see me back on here asking some questions!

 

Thanks again!

I've read the answers Ryan has got so far, just because I'm planning to enter the same project myself.

You all would be surprise to hear that someone has done such project already.

Check the link: http://www.microscopy-uk.org.uk/mag/artdec00/photodiode.html

Seems to me that if you can spring for a hasselblad, the meter should be a piece of cake.

I have been working on something similar for about a year now. The project has finally gotten a good start since I have more spare time now. I have a working prototype sitting on my desk. All I need to do is the software to handle the user interface. I plan to use a palm M105 for that. They can be gotten for about $30 on ebay. For the actual optics part I plan on buying a dead spot meter. I am releasing it all as open source under the GPL. The schematic is on the net at http://dlharmon.com/lightmeter.html The schematic only has one mistake I have found yet. If you plan to use it email me for details. I have tested the simple lightmeter mode, and it works fine. I have not yet written software for the flashmeter mode. I have not even started the palm software. I would like to get a few other people interested in writing the palm software. If you are interested in helping with it let me know and I will mail you a bare board. It should cost about $40 for parts. The board I have is an extra prototype, so it is not perfect. It is using surface mount parts. It should have 20-30 stops of range. I have verified that it can do at least 20 stops (30nA to 3mA). It is hard to test beyond that at this point. In a perfect world it should do 40 stops but I seriously doubt that.

 

I did not design and build this because I am cheap. In fact it has become a very expensive lightmeter. I designed it because I wanted to learn about it, and because I thought I could do it better.

 

If you are interested, send me an email. I will let you know when it is done and ready for anyone to build. It can be built without all the surface mount parts if you don't like them, but it will be larger. I hope to find a company to make small batches of my lightmeter so I can sell them on ebay.

 

Darrell Harmon

I must encourage you to try and build your spot meter. I have an an associates degree in electronic engineering. I have been working in the electronics field as an industrial electronics repair tech for the last six years. This involves a lot of reverse engineering and re-designing to replace obsolete IC's, to get our customer's machinary up and running again. Prior to this, I was hoofing it around the world with Uncle Sam's USAF. But electronics has always been my first love. And for the last three months I have been working on an Incident/Reflected Light Meter of my own design. I am near completion with only fine-tuning the calibrations left to be done. I use a BPW77NA phototransistor for the light sensor. This may or may not be the best sensor to use, but for the price, and its ability to "sense" in the visible light spectrum, I chose to use it. I use an 16x2 Liquid Crystal Display (LCD) as the visual interface, and push-buttons to allow me to make the changes, and take the light reading. The function of my program is Shutter-Priority. I set the ASA and Shutter-Speed, then take a reading and the fSTOP is given to me based upon the "sensed" light. I also have a function for exposure-value adjustment if necessary. My program uses an Analog to Digital Converter based microcontroller. The "sensed" light is converted to a digital value to be processed by my program. For my Incident Light Readings, I made my white diffusor dome from a ping-pong ball that I cut in half. A previous e-mailer mentioned that the calibration would be the toughest part of your project. I must agree whole heartedly. The hardware was easy for me. The coding was easy for me. But I have spent at least 50 hours in my back yard watching the sun go down while taking readings with my high-dollar analog light meter and my home-made digital light meter and coding it to agree with the other. I have found out something interesting in my region of the country. At sunset, it takes two minutes between half-stop changes. Ha-Ha. Well, Many times I would hit a stubbling block, but I didn't quit. The biggest hurdle was that I started out the first month-and-a-half with a low-dollar CdS Cell. It didn't give me the dark light sensitivity that I desired. And instead of the straight line linearity that I wanted, its light to dark characteristics were more like the left half of a bell-curve. This characteristic makes the analog to digital processing somewhat more difficult, although not impossible because I did it. But then I sub'd in an identical part number CdS Cell, and my light readings were off by two-stops. Not good. But with the phototransistor, I can sub in another one of the same part number and get an identical analog to digital value. Much Better. And why did I do all this? Because, like Mount Everest, it was there. And also for $60 in hardware, I could have my own light meter that performs better than the one that cost me an arm and a leg. I hope this helps and encourages you.

 

Peter A. McDonald