ExpoDev is very unique in that is uses highly accurate and test-produced reciprocity data for over 90 film and developer combinations. Phil Davis did the work of testing each and every film developer combination using selected exposure times up to 1,000 seconds or roughly 16 minutes. He also field-tested these results to ensure their accuracy. This is far above and much more specific than the data that film manufacturers publish for their films and developers, not to mention that ExpoDev's reciprocity data covers film and developer combinations across different manufacturers. Correction is not a one-size-fits-all curve; it is very unique to each film and developer combination.

What is meant by "selected exposure times" though. What this means is, when you tell ExpoDev that the shutter time you want to use is anywhere within the range of 1 to 1,000 seconds,  ExpoDev would then apply reciprocity failure correct and give you a corrected exposure time to use. This corrected exposure time may be a small adjustment for a selected exposure time of a few seconds or it may be several hours for a selected exposure time of 16 minutes (from 1 to 8 hours, depending on which film and developer combination you use).

There is a second part to reciprocity failure correction though and that is that the overall resulting negative density also changes with extended exposure times. Unlike exposure times negative density can change either direction, either increasing or decreasing depending on the film and developer combination used. ExpoDev's reciprocity data for these film and developer combinations includes how development time should be adjusted as well. This reciprocity data is used to apply an adjustment to the Average Gradient that is calculated as part of the exposure. It is this Average G value that is used to look up the development time that should be used to produce a negative that matches the target density desired (so that printing or scanning remains consistent and easy across all of your negatives).

Each Film Profile that you import into ExpoDev contains a two-part code expressed as a letter/number combination (e.g. D4, A6, etc…), The first part is for the exposure time adjustment code and the second part is the development adjustment code. For the exposure time adjustments there are 5 codes, A-E; for development adjustments, there are 7 codes, 1-7. When you export film test data from Plotter for Windows you select which code to use for that film/developer combination (Plotter has a table for all the film and developer combinations that were tested). Since you get to choose the code to use when you export your film test profile this also means that you can override the codes if your working processes need adjustments. You can even choose to export without any codes at all which will cause ExpoDev to skip reciprocity adjustment altogether.

In the next article I'll cover ExpoDev's adjustable Depth of Field calculator.

Until then I'm happy to say that ExpoDev version 1.0 has reached the final testing stages and if all goes well, it should be available in the Apple iTunes App Store very soon.

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:

  1. By owning Plotter for Windows and performing your own film test and analyses
  2. 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.

Today I’m going to start a series of short articles on ExpoDev for iOS. My goal is to talk about some of the unique features that set ExpoDev apart for other analog photography apps on the market. I’ll try to get something new out each week.

ExpoDev has many unique features that you won’t find anywhere else, such as calculating exposures based on personal film test data, the only exposure calculator which applies reciprocity adjustments that are based on actual lab-produced film tests for a multitude of film and developer combinations, the ability to calculate exposure and development to produce negatives which will closely mesh with different printing processes whether that be silver, platinum, digital hybrid/scanning, or any other alternative process. This is just the tip of the iceberg and I hope to talk about them all in upcoming articles.

But first an update: Beta 2 of ExpoDev for iOS is nearing release in the next few days. This release is about 95% functionally complete with the only thing left to complete being ExpoDev’s Depth of Field calculator. At it stands now, it is completely usable in the real-world to calculate and catalog your film exposures and development information. The exposure calculation system within ExpoDev have been extensively field test on other platforms for almost 10 years now (I’m referring to ExpoDev for PocketPC which has a smaller, private release). It is also a significant upgrade to the exposure calculation system used in ExpoDev for Palm, used by many of photographers today. I’ve personally produced hundreds of 4x5 B&W negatives using ExpoDev’s exposure calculator and I have never had a bad exposure (at least not due to ExpoDev – photographer error is another story).

After I get Beta 2 out the door I will write a few articles on ExpoDev’s unique system of exposure calculations and reciprocity adjustments, which is probably the most accurate reciprocity adjustment calculator in existence. Until then, here are some previous articles to catch up on things.

Previous ExpoDev for iOS articles:

Flux and Mutability

The mutable notebook of David Jade