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PhotoDOF Userís Guide

1. Installation

2. General information

3. The Depth Of Field Calculator

Circle Of Confusion diameter

Using the drop list to select a lens

Changing the focusing distance and aperture

Calculation and result window

Measuring Units: Meters and Feet

Diffraction

Few words about infinity

Precision of results

A note for Zoom users

4. The Aperture Finder

Results

Another word about infinity

Data sharing between DOF Calculator and aperture Finder

5. Contextual Help

6. Final words

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1. Installation

PhotoDOF is the Depth Of Field module in the Photographe 2.0 family of applications for photographers using the PalmPilot.

This module is composed of two screens:

Executables required to use this module:

The Parameters module (PhotoPar), which is distributed for free with any registered Photographe 2.0 modules, can also be used in conjunction with PhotoDOF, but it is not required.

To install PhotoDOF, you will need to download PhotoDOF.prc. If PhotoLIB.prc is not already installed on your Pilot, you will need to download it too. PhotoPar.prc can also be downloaded if you want to create and use predefined settings (recommended).

After downloading the required executables, you can launch them as any other Pilot app. The first time a module is installed and runs on your Pilot, it will register itself in the drop list at the top right of your Pilotís screen.

2. General information

When you run this module for the first time, like any other Photographe 2.0 module, a new entry is created in the drop list at the top right corner of the screen for each screen.

You can use this drop list to quickly navigate through all the installed Photographe 2.0 modules without needing to switch back to the Applications screen in the Pilot, however, you can also launch any module from there if you like. You can also easily switch from the DOF Calculator screen to the Aperture Finder screen or vice-versa by using the "<< Calc" or "Finder >>" buttons at the bottom right corner of the screen.

Even though this module can be used by itself as a stand-alone tool for Depth Of Field calculations, it is recommended that you use the Parameters module (PhotoPar). This module will allow you to create a list of lenses, with their predefined characteristics, that you will be able to use directly through a drop list in both PhotoDOF screens, thus avoiding entering a new focal length, and Circle Of Confusion diameter each time you switch lens. More about Circles Of Confusions (COC) later in this document.

Please refer to the PhotoPar documentation for more information about the Parameters module and how databases are stored in your Pilot.

3. The Depth Of Field Calculator

This screen allows you to perform ultra fast and accurate Depth Of Field calculations for any lens, given any focusing distance, at any practical aperture.

The following information is necessary to perform a Depth Of Field calculation:

The first three parameters are self-explanatory, the last one, however, needs some explanation.

Circle Of Confusion diameter

The Circle Of Confusion diameter (now referred as COC), to put it simply, is the largest dot you want to allow on your final negative for an in-focus object. On a picture, each object which is not in the exact plane of focus is by definition out of focus, however, all this is to the extent of the photographerís appreciation, and by selecting a COC, you decide how strict your criteria for an in-focus abject is.

In 35mm photography, a typical value for COC is 30 microns (0.030 millimeters or 0.012 inches) and what this means is that the negative being 36mm by 24mm. If the entire scene is in focus, you will end up with a minimum resolution of (36 / 0.030) by (24 / 0.030) millimeters, or 1200 by 800 dots.

Now, where does this bring us? To the print!

Knowing that you have a resolution of 1200 by 800 minimum on your negative, and if you want a final resolution of approximately 5 dots per millimeter on the print (or 127 dots per inch), then you can simply figure out that your maximum printing size for this negative should be not more that (1200 / 5) by (800 / 5) millimeters or 240 by 160 millimeters, or 9-1/2"x 6-1/3". If you want a final resolution of 10 dots per millimeters on the print, then you cannot enlarge the negative beyond 120 by 80 millimeters (roughly 4-3/4" x 3"), and so forth.

Of course, parts of the picture can be more in focus than the rest, i.e. have more resolution (typically, this is where the center of interest in the picture is), thus allowing you more room for bigger enlargements.

The bigger the film format, the bigger the COC can be since you wonít enlarge it so much, and this is fortunate since lenses tend to become longer with bigger film formats. This is why LF photographers usually find themselves playing in the f/22 to f/45 range to get a decent DOFÖ

Now that you know all about COC and what they mean, you can come up with your owns and experiment with PhotoDOF to see the impact of the COC to the final field of focus.

Using the drop list to select a lens

If you decide to use PhotoPar to enter all your lenses, you will see that you can assign a film format to each lens. And since each film format can have its own preset COC, this value is picked by PhotoDOF automatically. Example:

Letís say you have defined a lens called "Nikon 50mm f/1.4", this lens has an aperture mini of f/1.4, maxi of f/22 and optimum of f/8, and doesnít have half-stops settings. It is also used with 35mm film. The 35mm format requires a COC value, let say you entered 30 in it (30 microns as discussed earlier). Back in PhotoDOF, select this lens in the drop list, you will see that the following fields are automatically filled:

However, if you wish to touch up some parameters, like, say, reduce the COC, or change the aperture, you can easily do so, and the aperture mini, maxi and half stops settings will be taken in account. The drop list is just adding the convenience of predefined settings, but not locking you in them.

If the lens you pick from the list is a Zoom lens, an Up/Down control shows up next to the focal length field. You can use these buttons to easily change the focal length by increments of +/- 5mm. If the focus is set to the focal length field, you can also use the Up/Down arrows on the Pilot to change the value.

Changing the focusing distance and aperture

There are two ways of changing the focusing distance and three ways of changing the aperture.

You can change the focusing distance by entering it with Graffiti directly in the field, or you can set the focus (blinking insertion point) in the focusing distance field, and press the Up and Down buttons. When doing so, the distance increases or decreases by a percentage defined in the Preferences form (available as usual through the Menu). It is preset at 10% but you can change it to whatever between 10% and 100%.

You can change the aperture by entering it directly with Graffiti, or by using the Up and Down buttons right next to the field, or by using the Up and Down buttons when the field has the focus.

Up and Down will increase or decrease the aperture value following this rule:

Calculation and result window

There is no "Compute" button because all calculations are done on the fly as soon as something changes on the screen, my goal was to minimize user input to a minimum when I started developing my Photographe 2.0 modules.

The result window, at the top of the screen, is composed of two display areas. The top one, in big font, gives the field of focus in the main unit (meters or feet) and the bottom one in the other unit. If no DOF can be calculated (because of erroneous parameters given, or because no solution exists) then an error message is displayed.

Measuring Units: Meters and Feet

Both units can be used. You select which one you prefer by selecting m for meters or ft for feet in the check boxes next to the Distance field. The selected unit is shown in large font, the other in small font below. When m is selected, then the distance is assumed to be given in meters, and when ft is selected, the distance is assumed to be given in feet, so donít expect a simple switching between the big and small display, when changing from m to ft, the result will be different since it will be calculated in another unit.

Diffraction

This is an option, however anybody serious about DOF should always have it turned on, especially when using small aperture (i.e. beyond f/22) in LF photography.

Diffraction occurs when the lens is so stopped down, that light strays when encountering the sharp edges of the diaphragm, thus behaving like a pinhole camera. This phenomenon can be accounted for mathematically and surprising results can happen (like f/32 gives more DOF than f/45 in some combinations of focal length and focusing distance).

Usually, diffraction is negligible for apertures larger or equal to f/16.

If this option is on, you can run into situations where the DOF cannot be found because of either too small a COC or too big an aperture. PhotoDOF will inform you on the limit for both, and you will be able to choose wich to change (usually the aperture). It will give a message in the result window like "COC mini: 11 or f/stop maxi: 7.5".

Few words about infinity

Itís big!

I compute the infinity based on the focal length used. The default is 5000 focal lengths, so for a 50mm lens, infinity starts at 820 feet (250 meters), you can change this in the Preferences form, however, entering bogus values there will give you bogus DOF.

Precision of results

All results are rounded according to the following rule

 

A note for Zoom users

When using a zoom, I would recommend the following: in PhotoPar, create an entry in the lenses database for your zoom, and in the focal length field, enter the most used focal length with this zoom. Then, in PhotoDOF, youíll have to change the focal length parameter manually when zooming to a different focal length than the preset one.

4. The Aperture Finder

This screen is the counterpart of the Depth Of Field Calculator and allows you to find the best combination of focusing distance and aperture given two objects you want in focus.

This screen is very similar to the DOF Calculator screen, and only the bottom portion differs (below the second horizontal black line). In this section, instead of entering an aperture and a distance, you enter two distances, the near and far limit.

Since the calculation for this is based on a very complex algorithm, you might see a slight delay for the result to come up, however it should never exceed half a second to one second, and most of the time itís nearly instant.

All the familiar parameters from DOF Calculator are there and have been discussed in the previous section.

Results

When a result is found based on the two given limits, it will be displayed as a focusing distance/aperture combination. The aperture is the larger aperture found (i.e. yielding the most light), and will respect the settings for your lens (i.e. mini, maxi and half stops increments). So if your lens ranges from f/2 to f/16, and if the largest appropriate aperture starts at f/22, it will be reported as Not Found (exceeding the technical possibilities of your lens).

In the small display, below the large one, the actual field of focus for the calculated focusing distance and aperture is given as a reference, this is very useful if you want to know how much room you have in front of your closest object and behind the farthest.

Another word about infinity

Itís very big!

If you enter 0 or nothing in a distance field, it will be considered as infinity. Also, the two distance fields will respond to the Up and Down keys as explained in the DOF Calculator section previously.

Data sharing between DOF Calculator and Aperture Finder

When you switch back and forth between these two screens, you will notice that the previously found result is applied to the next screen.

For example, you found a combination of D=10 ft at f/22 in the Aperture Finder screen, now you switch to the DOF Calculator, and you will notice that these settings are set for you in the respective fields. This is to allow you to further experiment with different apertures or distances.

Also, when you leave either screen to switch to any other application and come back, you will find all parameters as you left them. However, if a lens was selected, and the default parameters changed, then returning to the DOF screen you left will reset these parameters to their preset value.

5. Contextual Help

Help is available from both screens by tapping on the little "i" icon on the bottom left corner of the screen, or by selecting Commands/Help from the Menu.

6. Final words

Any bug regarding erroneous calculations, crashes, or even user interface problems can be submitted to me at:

PalmPhotographe@yahoo.com

You can even send me nice things!

I worked hard at making this module easy to use and bullet proof, however, neither the PalmPilot OS nor me are infallible, and I am open to any suggestions and wish lists.

Please register this software, not only you will get rid of this nasty About box always coming in your way, but you will sleep better at night, and youíll have the right to flame me!