Need help creating a characteristic curve from film testing

[rickwinkler]

It really sucks gettin old! I touched on 4x5 cameras and film testing in an advanced b&w class in 1990. Now that I've grown up (ya right) I want to be a great photographer, using the one format that makes a difference. Which of course means that I have to do it right but my math skills got up a left a long time ago. I have all the handouts, examples and helpful hints from that 1990 class to create one of these curves from testing your film. I remember the D-min (.1 net above FB+F), beginning of zone III (.2 net above FB+F), middle of zone III (.35 above FB+F), beginning of zone v (.8 net above FB+F), middle of zone v (.95 net above FB+F) and D-Max (1.10 net above FB+F). The piece that is missing is how the information is populated along the x-axis, this information is the relative Log 10 exposure. It goes from L to R reading 3.20 to 0.00 in the same increments as the density numbers of the y-axis. There are 21 entries along this scale to correspond with the 21 steps of the step tablet used. I have an old analog densitometer good for only film or slides so another question is shooting a reflective step tablet and being able to use those know reflective values when reading them as a negative. This stuff was hard enough when I was young and smart, it sure would be nice to resurrect some of those dead brain cells right about now. Any help would be appreciated.


Thanks in advance,

Rick

[N Dhananjay]

The x and y axes are typically on the same scale unit of 0.3 - x axis is log exposure (each unit of 0.3 represents a doubling or one stop), and the y axis is density. I would caution you against using some set value for each zone - depending on the shape of the curve, these values (especially in the middle and top end) can be quite different. If you want to remind the grey cells, I would urge you to visit the library and pick up a copy of 'Beyond the zone system" by Phil Davies.

In my opinion, with negative film, the most important thing is getting enough exposure in the shadows to get off the toe of the curve. People who loathe testing halve the film speed on the box, others shoot subjects and adjust till they get the shadow density they desire, others test with step tablets and densitometers.

If you are intersted in the characteristic curve and decide to go the last route, the easiest way to run film tests is probably to contact print a step wedge, develop the film and measure the densities. You will not be measuring the effect of flare but should get a good idea about the characteristic curve of the chosen film-developer combination pretty quickly.

Cheers, DJ

[Shen45]

Rick I use the BTZS system and can really recommend the WinPlotter software.

4 or 5 sheets of film tested using Phil's methods will yield you so much useful information. Talk to Dennis or Fred at the ViewCameraStore.com and they can explain the system or log onto www.btzs.org and read some of the articles.

Steve

[Brian Ellis]

I second Steve's suggestion. I've used The View Camera Store to test several different films. It cost about $35 but well worth it IMHO. You'll have your own film speeds and your own development times for whatever film you choose, ranging from about N - 2 to N+2. Much easier than doing your own tests and by the time you finish you own tests you probably would have spent $30 or so on film alone, plus you'll get much more information than if you did the tests yourself.

[rickwinkler]

This is great stuff, I was focused on the procedure that I had done before. I didn't stop to think there might be advancements, what a concept. I really do appreciate all the info, I've already ordered the book and will get with Dennis or Fred at the ViewCameraStore.com. I'm really excited because this helps lift a big weight off my shoulders. I almost feel like doing back flip but I never could do one when I was young so I'll have to find something else to do.

Thanks again,

Rick