Showing posts with label cottage tips. Show all posts
Showing posts with label cottage tips. Show all posts


Cottage Tip: Building a small exposure meter-Part III

When I finally got a working panel voltmeter (measuring range 200 mV) I got an unpleasant surprise; it needs a separate supply, other than the circuit, but it wasn't specified in the catalog I bought from. There are also voltmeters able to share the same power supply with the rest of the circuit (the so-called common-ground type), but unluckily not this one. So I needed first to make somehow a split power supply with the same battery for both the sensor circuit and the voltmeter, with the available resources. So I redesigned the circuit a bit. The aim is to keep both voltages (for the meter and the sensor) as »far away« as possible from each other, preventing to get faulty readings. Below, see the circuit schematics.

 After that, I needed to do a quick test to such a circuit on the breadboard. I also needed to do a short-circuit on one contact pair on the voltmeter, in orderto get into the 200 mV range (following the instructions). Oddly, there was already one short-circuit present (factory-made). These »shorts« also set the decimal point. So two decimal points are now present. Nothing dramatic, only funny somehow (note in the photo).
As the weather wasn't really appropriate (for several days) to fully test the meter outside and in sunny conditions, I relied on my instinct so I soldered the final circuit on the prototype board.

I then made the apertures on the enclosure for the display, the sensor and the activating switch. The battery holder is just an ordinary AAA battery holder shortened by about 15 mm and glued together (the batteries A23 and AAA are of the same width).

the battery holder
Finally, I put everything inside the enclosure: switch, panel meter, sensor, circuit and battery-using solder and glue. As it seems, it works nicely! Now, a necessary addition should be to mount (below the panel meter) also an exposure calculator wheel to be able to set the exposure settings. But I first need to buy some plastic printable film to do that.
The inside of the exposure meter
The finished "product"
 Should the precision of the meter be a bit off, I will still need to change the Zener diode in charge to power the panel meter, i.e. using one with a bit lower voltage-just enough to ensure the meter to work, by changing the existing diode in the circuit with another one.


Cottage Tip: Building a small exposure meter-Part II

I got (almost) all I need to build the actual meter (save the voltmeter, it should take quite longer to come, not really sure why). I got the LDR sensor, so the first thing I did was to build some kind of enclosure and light diffusor around it. I just recycled a piece of black plastics for the base and the middle of the (Fuji) film canister cap for the diffusor. I drilled two holes in the base for the sensor leads and painted the inside of the cap with white opaque nail polish (taking care to make an even layer). When the nail polish dried, I glued the sensor on the base and then glued the white-painted cap onto. I know, it is not exactly a dome-shaped diffusor like in commercial meters, but probably (hopefully) will do the job more or less in the same way. It is more like a »hybrid incident light adapter« between the dome-shaped and the flat diffusor (the ones used to asses the contrast ratio). See photos below.

Starting materials for the sensor: light-dependent resistor (LDR), black plastics for the base, white nail polish and a Fuji film canister cap.

LDR glued to the base, and the cut mid-section of canister cap painted inside.
The sensor assembled on the breadbord (don't mind the resistors nearby, they remained from a previous project).

The so-prepared sensor was ready for testing! Unfortunately I came home quite late, so I catched the last sun rays. There wasn't a 15 EV intensity anymore, but only about 13.5 EV.  Then, I measured the response-resistance down to about 4 EV at different values.  I then plotted the dependence of LDR resistance against light intensity (EV). The outcome was quite a nice exponential curve (as it should be) with a very good correlationship.

The testing rig: multimeter measuring sensor's resistance and the Minolta exposure meter for getting the actual EV value.

I then used the obtained formula of the curve equation to calculated the predicted resistance at a given EV value (also for the points I did not measure). Then, the calculated resistance values served to calculate an appropriate series of voltage values to be obtained between Rx and R1 (voltage drop across R1; see the previous post). For that purpose I used the first part of the formula:
UOUT1= (UZ2 * R1)/(Rx+R1)  
Where UZ2 is the voltage of the Zener diode (supplying the voltage to Rx and R1), Rx is the value of the LDR and R1 is the chosen resistor value.
Now, I must confess, I wasn't really picky about the Uz and R1 values, but I tried to match them to what I have at hand (and/or combining various values), but anyway, I wanted to get satisfactory results, at least. So for Uz I chose a Zener diode with voltage drop of 3 V and for R1 I chose the value of 3200 ohms (3k+2x100 ohm).
I got this, quite a linear curve:

The curve equation now tells me that if I want to get the output of about 10 mV/EV I first need to add (offset) 1290 mV to this (voltage) signal and then divide it by a factor of about 28.4. Very luckily to me,  1290 mV is quite exactly the voltage drop of 2 regular diodes connected in series(cca 1.3V)! This is not necessarily the case, but luckily for me, it was. Otherwise, I would need to use another Zener diode and a trimmer to adjust the offset voltage, in a slightly different circuit arrangement. Using a different LDR  and light diffuser would certainly yield different values and curves. For the voltage divider I didn't use exactly the factor of 28.4, since the calculation  gave too much shift from the theoretical values, especially at high EVs (where the meter is used mostly). Given my resistor choices, I opted to use 1267 ohms for R2 (1k+220+47 ohm) and 47 ohms for R3. This gives a ratio of 1:29.57. By applying this ratio and the voltage bias of 1300 mV (two diodes), it gave me the following (calculated) measurement error at different values:

At first, it doesn't look like nice. But, we seldom use a meter below 6 EV (very dim light), and the error of around 0.3 EV is totally acceptable in practice for cameras and meters alike. Only between 11 EV and 13 EV the error is quite large, but as long as we know how much the error is, we can always correct for it. But clearly, all this is still theory only. The practical measurements will tell how good or bad the meter is.
Anyway, at least I came up with the final version of the circuit, with resistor and diode values to test, and hopefully, solder into the circuit board. See below (this is only the signal part of the circuit). But let me stress once again: this circuit is (should be) suitable for MY very own case of sensor, not necessarily (or likely) yours!

The signal part of the circuit I came up with.
The diodes D1 and D2 are just ordinary small-signal diodes. The Zener diode, as said, has  a drop of 3 volts, while the resistor Rz has been set arbitrarily at 4.7k, just to get a current somewhat higher than 1 mA, (at high EV values current can approach about 1 mA in this configuration). Voltage drop across Rz is 7.7 V (12-3-1.3), divided by 4700 yields about 1.6 mA. The photo below shows a more general (and probably also more appropriate) case of a signal circuit-using another Zener diode and a trimmer potentiometer to adjust the bias voltage. The latter is probably the largest source of measurement error in such a meter:
A more generic signal circuit.

During the weekend I'll test the sensor and circuit on the protoboard (»breadboard«), and I am quite anxious to get the results, which I'll promptly report to you. If time will permit, I'll also get in the final construction till next time.
Silver regards

CORRIGENDUM: While the circuit in the penultimate photo (without the trimmer pot.) is in principle OK, your restless editor forgot for a moment a basic aspect of Ohm's law, and a vital coefficient....Therefore, the correct values for R2 and R3 are 1.267 M ohm and 47 k ohm, respectively. I apologize for that.


Cottage Tip: Building a small exposure meter-Part I

It has been said that necessity is mother of all invention, but I disagree. Other »mothers of invention«, in my view, are also vanity, frustration and other »virtues«, but they are often confused with the first mother, necessity. Anyway, there too many things to list humans invented just for the sake of their own satisfaction, not really necessity, and some of them are even nice gadgets.
I always »needed«-actually just wanted to have-a small, pocket-size exposure meter, but never wanted to spend a small fortune for one. I have my trusty, almost 20-year-old Minolta Auto Meter III which never let me down. But it is a bulky meter. I just wanted to have a small meter when I get out with a 35 mm camera, with no bags or whatever. Thus, the meter should fit in a small pocket. You can even get an old used one for about 20€, but they tend to be unreliable and in many cases, not working. You can get the small and sweet Sekonic Twinmate, but I just never wanted to spend some 100€ or so for one. Nowadays even less so, since for the same money you can buy a film SLR in very good condition....
So, the plan is to build one simple but precise (enough) incident light meter for about 20€ or so in materials and components. The exp.meter must be:
-simple (both in operation and circuitry)
-precise within ±0.3 EV
-usable at least from 15 EV (the »sunny 16« conditions) down to about 4 EV (exposure value, ISO 100)-this is also the range of many commercial meters
I already checked the availability/pricing of components, but they still need to be the mean time, I'll lay down the theoretical aspects of this building issue.

The sensor
The easiest approach (and maybe even the most effective) is to use a CdS (cadmium sulfide) photoresistor (light dependent resistor –LDR). It has  the nice property of a logarithmic response (of its resistance) to lighting conditions, but inversely (the resistance decreases with increasing illumination).  The EVs we deal with, are also a logarithmic arrangement, since by every EV step the lighting conditions change by a factor of 2 (1 stop). We can thus get (with a bit of gimmicks) the electrical output (current or voltage) directly related to the EV value. But we also need to make first an appropriate light diffusor (and attenuator) for the sensor (since they are quite sensitive).
The display
The nicest way would be to use an analog milliammeter or millivoltmeter, but unfortunately such small meters are very hard to find, plus they are substantially more expensive than their digital conterparts-and then you can be quickly out of budget just for the meter! Digital millivoltmeters (we need them in the range of ±200 mV) are quite expensive (10-15€), more than half of the budget, but they include all the necessary circuitry for a precise metering. They usually run on 9 volts. You just provide a battery source and the measuring leads for your signal, and of course, some room in the housing of your meterJ The use of a 7-segment or LCD display (while cheaper) would dictate the use of the necessary A/D converter and drivers chips, which would substantially complicate the circuitry and eventually, you could spend (more or less) the same amount of money.
The battery
An ordinary 9 volt battery is just fine, but not of my taste-too heavy and bulky. Instead, you can get a 9V battery of the 23A-type(used in remote controls), but very rare. Or you can use its 12v counterpart (also used in remotes), since its easier to get and cheaper. Smaller than a AAA battery, and you can even adapt a AAA battery holder for it.
The housing
Any plastic case of suitable dimensions can do the job-you can even recycle some old stuff. Or you buy one for a few € or $. Just be sure it can fit the voltmeter, the battery and the circuit. Along with the housing, we also need a switch to turn on the circuit for metering.
The circuit
I really like simple things, so I did not include any integrated circuits, only discrete components, and the least amount of active (semiconductor) components as well. In the hand-drawn circuit draft shown below there are no actual values shown, since I don't know yet how the LDR will behave. Only after that I can calculate the actual values to fit my needs. But I do know that I want the output to be 10 mV/ EV (for increased accuracy); at 15 EV (»sunny 16«) I want to get as close as possible to 150 mV, while at the low end I want about 40 mV for 4 EV.

The resistors Rz1 and Rz2 are just regulating the currents for the voltmeter and the sensor circuit, respectively. The first Zener diode ZD1 serves to supply the 9V needed for the voltmeter, while the ZD2 will be set later, when the LDR behavior will be known, as also the values of other resistors R1, R2 and R3. But we do know that the output will be according to this formula:

UOUT= (UZ2 * R1)/(Rx+R1)  * R3/(R2+R3)

So we have 4 parameters to play with (UZ2 and R1-3) to adjust them to our needs. Maybe we can later add a couple of diodes to adjust the input voltage level, but we'll see. Anyway, I like this simplicity and I just can't wait to do the actual test, next time.


Cottage Tip: Densitometry Simplified

Densitometry and optical density seem to be a very abstract topic to too many photographers, but they're not. Optical density is in fact a very handy way to express the loss of light through a medium; in our case photographic film or paper. It is a valuable tool for image analysis.
Optical density is defined as:
OD = Log10(Io / I), where Io is the non-attenuated light intensity (e.g. light reflection from blank paper base) and I is the attenuated light intensity (e.g. light reflection from an image area of the same paper)
In case when Io / I = 2 (the light intensity halves, i.e. is reduced by one stop), the density value equals to 0.30 which is a very handy number to deal with.
Very unfortunately, dedicated densitometers are quite expensive devices, even used ones. A new one can easily cost you about 1000 € or even more. If you're lucky, you can find a used one for a few 100 €. (And you still spend the same amount of money as for a SLR in good condition). Here I show an example how to make densitometric measurements of reflected light (i.e. from prints). Everyone who has ever dealt with alternative printing techniques has noticed the expression »image density«, be it for a cyanotype, platinum printing, and of course gum bichromate printing. Or any other technique. You can easily live without densitometry, but for getting consistent and predictable results in your printing, it is better to use it, especially in color or multi-layer printing. And you don't even need a densitometer. For densitometric measurements of acceptable precision, you need just a decent SLR or DSLR with spot metering capability-it is better to have a camera with 1/3 stop setting increments, but you can get along with a camera with 1/2 stop settings (like mine). For total (visual) densitometry, this is all you need. But for measuring the density of all three image-forming colors in color printing (yellow, magenta, cyan), you will also need a set of RGB filters. They need not to be the expensive optical quality filters-a set of RGB lighting filter gels (like Lee) are just right for the job, provided they faithfully represent the three primary colors (red, green, blue). You can buy a set of them online for a few €. I cut them in 75x75 mm squares and I hold them in front of the lens when I take the measurements.
The measurements were made with my Canon EOS 5, set in Av and spot mode. Aperture f/2.8 and ISO 100. Illuminated by window light.
Measuring is easy, just set your camera in aperture-priority mode at the aperture and ISO setting at your convenience, set the spot-metering mode, and place you print on an evenly illuminated surface. And you don't even need to have a focused image (actually it is better not to). First take the reading of the paper base (in secs) and then on the spot on the image you want to measure.
Say, you got these two readings for paper base and your spot of interest, 1/45 s and 1/15 s, respectively. Now you calculate the logarithm of their inverse values (actually their camera readings):
OD = Log10(45 /15)= 0.48
This value tells you that the reflected light on that spot is attenuated by about 1.6 stop.
For the sake of illustration, I prepared a sheet of drawing paper (see above) with spots of different colors approximating the black and the complementary colors (yellow, magenta and cyan) differing in intensity (density). They are made with pastels and are by far not ideal, but they show the basic principle anyway.
When you want to measure the density of the yellow color, you measure it with the blue filter in front of the lens, since blue is complementary to yellow. For magenta, you use the green filter. And for cyan, the red filter. This is because you want to block the other two colors during your readings. Write down your readings and the calculate the logarithm values. These are the densities of selected image spots. Easy, isn't it?
Of course, these measurements are not super-precise, but they can help you a lot when you engage yourself in alternative printing.
The tools I used to measure the densities: my trusty SLR, and for YMC colors, the 3 Lee filter gels-red, green and blue. Pocket calculator not shown :)


Cottage Tip: Revitalize an old Polaroid!

Probably you recall when I was ranting about the »new age« instant photography? Well, this time I thought it would be nice to offer an alternative to this new age stuff. I know, this is nothing new, many people did it many times, but nevertheless, there are still many of you out there not (yet)  having an instant camera, like me, until quite recently. Given the available instant film choices today, getting a Polaroid Land camera is probably the best option, since pack film is regularly available, and at a moderate price-Fuji FP instant film. A nice feature of this film is also the possibility to reclaim the remaining negative, but this will be the topic for another post. The Land cameras are great eye catchers with their bellows, and some of them produce photos of respectable quality (but they cost more). Most of them not, like mine, having a simple plastic lens, but they still have (or maybe for this very reason) their own charm, and you can get them for very little.
Polaroid Land cameras-they are so sexy, aren't they. Jean Pierre, thanks for the photo.
The main issue is where to get the battery for this 4-decades-old camera? The majority of Pola Land cameras use the 3V 532 alkaline battery, which is quite difficult to find nowadays and is also quite expensive-like as much as you spent on the camera itself! In case you don't own a rare or collectible camera, don't feel too sorry to make a bit of surgery on your Pola Land wiring. Just cut off the old battery contacts and solder a plastic insert for two 1.5V AAA batteries instead. Just make sure to have these batteries connected in series (with 3V output) and having them soldered to the right polarity! That's it! It's a 10 minute job, more or less. 

A new battery holder with two AAA batteries. Note the cut original contacts.
The new battery holder fits just perfectly inside the battery compartment.
You will also need to get rid of the remaing plastic tabs-retainers (for the original battery). It is an easy job: just move them in rear-forward motion for some time, and the tabs will just fall off. Now, the new plastic battery insert will fit nicely in the battery compartment of your old Polaroid! It is worth to take a look at the Land List where types of batteries are listed for single cameras. If you own a camera which uses a 531 battery type (4.5V), then you'll have quite a bit of trouble. Probably is just easier to get a 3V camera instead.
If you're unaware of the camera conditions, it is a good measure to check (from time to time) the voltage of the batteries. These old cameras can draw some current even if the are not  in use. And when you just want to use them, the batteries are too low. So, don't waste the instant film because of empty batteries, just have a pair of fresh batteries for backup-they are cheap!


Cottage Tip: Keeping Humidity under Control- Part 2

Keeping your photo bags and cases free from moisture is only part of the story, especially if you keep them in an enclosed environment, a closet or drawer, without circulating air, where moisture can accumulate (especially in the cold spots of the house). Over the years, I have accumulated quite some gear, so I needed to buy a small closet where to keep my toys. Now, you can buy an air dehumidifier and replenish the adsorber (calcium chloride) as time goes by. The trouble is, these dehumidifiers are quite bulky, taking much of your precious closet space, as it was in my case. It's still better to have this place for storage of more lenses, isn't it? I came up with a cheap solution: a dehumidifier made from a soft drink bottle.
This is all you need: a stocking, a bottle and calcium chloride.
Put the adsorber inside the stocking of the assembled "device".
Just get a wide-neck bottle and put inside a short nylon stocking. Fix everything with one or two elastic bands. This stocking will serve to contain the adsorber (calcium chloride),  suspended above bottle's bottom, while the wide bottleneck ensures more moisture adsorbing capacity. Fill the stocking with calcium chloride (it is much cheaper to buy it bulk). With time, the liquid (saturated calcium chloride solution) will accumulate on the bottom. Dispose the liquid down the drain (it is safe) and replenish the stocking with fresh calcium chloride as needed. That's it! 
The dehumidifier in its place, along with a thermo/hygrometer.
The same thing can be made from a jar, of course (provided you have enough room). Oh, and a good measure is also to have a small, cheap thermometer/hygrometer located in this place (you can get one for a few bucks). You will be amazed how much humidity changes, depending on the weather. Our goal is to keep relative humidity under 60 %, which is thought to be (mostly) safe in terms of fungal growth. However, r.h. under 35 % is also bad, since lens and camera mechanisms are more likely to get too dry (less lubrication). Fortunately, the latter condition is less likely to occur, in most places.


Cottage Tip: Keeping Humidity under Control- Part 1

Humidity is one the worst enemies of your cameras and lenses! We all know that under prolonged humid conditions, especially if stored in the dark, fungal growth can begin inside your beloved lenses! The best cure is, of course, keeping your equiment in constant use (fungal growth is quite sensitive to light). But most of the time, our beloved toys reside in a bag or a case, in the dark. Unless you live in an arid environment, we need to make sure there is not enough moisture inside to initiate the growth of the evil fungi! Fortunately, fungal growth is quite a slow process, and won't happen overnight! Many photographers just put (intuitively) inside a bag or two of silicagel they recycled from a shoe box or other purchased goods. The problem is, this silicagel is probably already exhausted, so it has no capacity left to absorb the moisture. Plus, it usually has no color indication whether is exhausted or not. Most of the people just put inside these little bags and forget about them for good! Fourtunately, most people don't have problems with fungi, but some of them do, sadly. 
This is all you need: fresh silicagel, a film canister and a sharp tool (e.g. scissors). Rightmost: a bag of exhausted silicagel.
This is how a punched canister looks like.
Left: film canister with fresh silicagel. Right: canister with exhausted silicagel, notice the color change.
 The real solution to the problem is to buy silicagel beads with color indicator in bulk-you can buy half a kilo or so for little money online. As the silicagel gets too wet, it turns its color from orange to dark blue (it looks like caviar-before and after-salmon before, beluga caviar after J). So, buy silicagel in bulk, and you can regenerate it many times by (re)heating it! Next problem is the container; I simply use a (translucent) film canister, finely punched along its surface. Pour the dry silicagel inside and close the lid. A canister or two will do their job for a few weeks or months inside the bag (or case), but not forever! Moisture penetrates more than you can imagine inside your bags and cases (unless you have everything sealed with plastics-not really practical), so a regular check is advisable. When it comes to regenerate, simply put the silicagel in a shallow (glass or metal) container or pan inside the kitchen oven for an hour or so around 100 °C. When it turns back orange in color, you're done! When not in use, keep your silicagel well sealed against moisture. The humidity in your closet or drawer, where you keep your gear, is also important. We'll cover this in the second part.
A note of caution: with time, some fine dust will occur, due to silicagel's self-abrasion. Do not breathe the dust, it's not friendly to your lungs!

About Cottage Tips

Dear Readers,
As already promised, we'll feature a series of technical contributions, and among them there will be the so-called Cottage Tips. Essentially, it will be a »how-to« series of short (or longer) posts, dealing with various inexpensive technical solutions for improving your photo-gear, upgrading on a tight budget, or even making a piece of equipment not available in the stores. Not necessarily all contributions will be strictly dedicated to film photography, but also for general photographic usage. I am sure some of the contributions you'll find very basic or redundant, something you've been knowing about for ages, but most of them not. We also need to keep in mind the newcomers to (film) photography; they need all the information we can give them. On the long run, I am sure with these tips we can make our photographic endeavours a little bit more comfortable, easier, and hopefully cheaper, too.
silver regards