Added H&D curves to my Film Log webapp, though I'd share

[m00dawg]

I kinda expect folks here that know how to make H&D curves already probably have their process setup the way they want, but nonetheless, I thought I'd share what I've come up with:

https://www.youtube.com/watch?v=PGKP2upe2aw

Of note, I still actually do H&D curves on paper to calculate the gamma and contrast index. It's also kinda nice meditation time of sorts but I do like to be able to see different film curves sort of "at a glance" and also it's nice if I need to look up a specific test to know what development time I should shoot for.

Since I made the video, I finished implementing the missing bits (like being able to add step tablets - that's kind of important) so it is now usable, if still perhaps a bit rough around the edges.

I've been thinking about how to approach gamma and CI but haven't quite figured out the best way to do that. I need to figure out trendlines first and also need to work on how to find values on the graph (I'm using charts.js here for the curious).

Final note, for Windows users, the BTZS Windows app, while I think fairly dated, likely does all this (and more) but for me it's nice to have all this in one place as I also use my app for film logs, tracking my replenishment, darkroom printing, film stock, holders, etc.

[ic-racer]

I have been using the first 10 or 11 steps after 0.1 as my personal "Contrast Index" in all my computations ( a linear regression of those points, exactly). I started using a spreadsheet to do this back when they first became available on computers and I kept to the same method all these years.

My spread sheet keeps getting more and more complicated, so now it calculates W-speed and ASA speed too.

The nice thing about W-speed is that, like 0.3G, it is independent of development. The only problem is one needs a computer to calculate it. Since a computer was not common back then, they came up with the ASA method you can do on the graph paper with a pencil. Since I have a computer, I can use the W-speed method instead.

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[m00dawg]

Oh very nice! Curious what is w? That one is new to me.

My ISOs have been a little off I think, which probably makes sense since my LUX meter only works in whole steps and I'm also using an enlarger (over a sensitometer) which is skewing my exposure time as well. They seem to trend slower than I'd expect for many films. HR50 for instance is 3, which seems crazy low, although in my film testing, that actually did give me a rather nice looking negative when I did a contact sheet, so *shrug* Even so nearly every film I test gives me a lower ISO - just depends on the degree. So I've mostly just gone to pictoral testing for ISO, at least for now until I figure out something better.

My CI's and dev times and things seem pretty spot on though.

[ic-racer]

The reasearch by Loyd and Jones showed the best correlation between print quality and speed was with a speed point at a tangent of the toe at one-third the gamma (0.3G) line.
This is hard to get without a computer. So there were three approximations of this 0.3G to make life easier in the pre-computer era:

Delta-X
W-Speed
ASA Triangle

All three of these are about the same at approximating 0.3G. ASA triangle requires multiple tests to find the correct sample to fit in the "ASA Triangle." Delta-X requires a look up table but you need to find a specific point on the curve by hand (you have to make an arc at log 1.3 from your 0.1 point.) Finding the arc at 1.3 out from the 0.1 point with Excel is challenging, but not impossible.

The W-speed also requires finding a special point on the data set, but the math set in Excel had enough power to figure it out. So that is why I use that method.

[m00dawg]

Gotcha, that's some really interesting info thanks! That gives me quite a bit to think about there. To this point I've been largely using the Kodak method (using their H740 workbook). Credit has to go to Greg (The Naked Photographer on YouTube) for walking through a lot of this as well. I've read AA's Negative and BTZS but neither gave me the "aha! that's how you do that!" moment when it came to creating the graphs.

It's already been useful, but the above sounds really really interesting!

[ic-racer]

There are some proponents of Delta-X method, but my friendly challenge to see a spreadsheet make the ark as one would do with a compass and find the intersecting point has drawn a blank.
BTW I have done tests to show the common x-ray sensitometers on Ebay work fine for B&W film testing. Plenty available for less than $100. Last one I got was $20.

https://www.photrio.com/forum/threads/x-rite-334-sensitometer-inspection-and-analysis.180579/