ExpoDev is unique among analog exposure calculators in that it uses actual personal film test data to drive the exposure calculation process. This probably makes ExpoDev the most accurate B&W exposure calculator in existence as it uses your personal data that is derived from your equipment and your working processes.
Here are some details on what that means exactly and how it works.
Getting film test data into ExpoDev is now easier than ever
With previous versions of ExpoDev (for Palm and PocketPC devices), getting data onto a device was cumbersome at best. ExpoDev had to rely on the software tools supplied with each of these devices to sync the data. For Palm devices, that software won’t even run on modern operating systems like Windows 7 or OS X.
I’m happy to say that those issues are a thing of the past now. ExpoDev for iOS can open film test data files directly with no computer intervention. That makes this new version of ExpoDev truly platform independent. Since all Apple iOS devices have both Internet and email connectivity, you can simply email the film export files as attachments and open them directly on any iOS device. ExpoDev would then import them directly into your library of films.
That’s not the only way though. If you already sync your iOS device with Apple’s iTunes (available for both PCs and Macs), you can also import and export data files for ExpoDev directly using iTunes. Down the road, there will be other options like an online film test database to allow you to retrieve your stored film tests. This last option will be especially useful to people who have used the View Camera Store’s film testing service in the past as it will allow them to retrieve their test results at any time.
How do you get personalized film test data?
ExpoDev film test data is produced by a companion software program, Plotter, that analyzes your actual film tests to produce the charts that drive ExpoDev. These film tests are unique in that they very effectively test the film and developer combinations you actually use. This process will yield very personalized film test data that is tied to your personal working methods and equipment. Once Plotter analyzes that test data, it can then export it to an Export Film data or .XDF file that can then be used by ExpoDev. You can get your own personalized film test data files in one of two ways:
- By owning Plotter for Windows and performing your own film test and analyses
- By using the film testing service from ViewCameraStore.com, who will help you by sending you pre-exposed test film to develop that you then send back for analysis. In return, they send you your personalized film test files.
Either method is effective, it just depends on how much you want to personally do. If you’re serious about testing materials, shoot lots of different film/developer combinations or perhaps want to target several different printing processes, you might think about owning and using Plotter yourself (available through ViewCameraStore.com). However if you just want to get better negatives than you do now, you might consider using the View Camera Store’s film testing service to quickly get up and running.
What does an Export Film data file contain and how is it used?
Film analysis produces two main charts that are used by ExpoDev when calculating exposures, the Average G (Average Gradient) to EFS (Effective Film Speed) lookup chart and the Average G to Development Time lookup chart. For each scene that you meter, ExpoDev will calculate the SBR of the scene (Subject Brightness Range) and the corresponding Average G. It then uses the film test charts for your selected film and developer combination to lookup the EFS and the Development Time to use when calculating the exposure. This process directly ties the film test, your equipment, the scene, and the resulting exposure together in a closed-loop which makes for very accurate exposure calculations. In actuality, there are many other things that are also taken into account such as the Paper ES (that printing paper’s Exposure Scale, which controls the target density of your negatives), Lens Flare, Filter Factors, and film test reciprocity data (which will be covered in another article as it is its own topic).
In the meantime if you want to do a “deep dive” on understanding and reading a film test as produced by Plotter, there is an article on BTZS.org written by Phil Davis that gets into many of the details. That article is located here: How to read a film test – by Phil Davis
If this is the first article on ExpoDev you’ve seen, be sure to check out the others on this site (and check back again for future articles).
Next time I’ll cover how ExpoDev uses the reciprocity test data as produced by Phil Davis to adjust both exposure and film development for over 90 different film and developer combinations.