Film speed testing: Help! am doing something wrong

[aruns]

Hello LF'ers,
I need some help with figuring out what I am doing wrong:
I apologize for the long post, but I wanted to add relevant details.

Objective/background:
Am trying to determine my personal film speed using Bruce Barlow's instructions in his book (Great book, thanks Bruce!).
Film: Arista Edu Ultra 100 4x5 film. Lens: Rodenstock f/6.8 90mm. I don't have a densitometer, so I wanted to try it with 0.1 ND filter.

Setup:
* flat, dark brown towel in almost-even shade, Sunny day
* filled the ground glass with subject, set lens to 90mm from film plane ("infinity?").
* metered the center of towel, with spot meter, stopped down 4 stops.
* stayed with 1/4 and 1/8 sec for shutter speed, to avoid reciprocity variables.
* ended up with four exposures.
A. around f18, 1/4 sec. (ISO 100). Exposed full slide (by mistake).
B. around f18, 1/8 sec. (EI 200). Exposed half slide. Remaining half should be FB+F.
C. f/16, 1/4 sec. (EI 75). Exposed half slide. Remaining half should be FB+F.
D. around f/14, 1/4 sec. (EI 50). Exposed half slide. Remaining half should be FB+F.

Development:
Rodinal "normal" 1+50 development: 7 minutes at 68F (I started with 68, but it crept up with time. the room / tap water temp was about 75F). Gentle Agitation: 30 sec in the first minute, then 10 sec / min.
Stop: I used plain water for 2 minutes.
Fix: Ilford Rapid fix - 1+4, for 5 minutes.
Wash: 5 minutes in water.
(I made a mistake during development - I lost track of slides between A and B, as well as between C and D. But I do know which sheets are A&B and C&D).

Problem:
The negatives do not show the density differences as they should. Please see attached images.
1st pic shows the negatives in a sleeve (with a white paper underneath).
2nd pic shows negs with 0.1 ND filter placed on the FBF area of one negative. The exposed areas of the negatives are nowhere close to how it should look.
3rd pic - it is a scan of RC print I made using the film and lens, exp. @ 100. I know this combo works.. But what am I doing wrong? why this under exposure?.. (I checked the lens/shutter, but it seems to open properly).

Please help, Thanks much in advance!

Regards,
Arun

[ic-racer]

The density you got 'is what it is.' That is to say the EI in your system is going to be lower than your lowest test. That could easily be the case for that EDU-100 film. Which is to say try doing your test at EI of 50, 25, 12, 6 etc and see what you get.

[ic-racer]

Also, consider using a light table when checking the negatives. If you set any ND filter on a white piece of paper, its apparent density will double. The light is filtered once when it goes through to the paper and a second time after it bounces off the paper on its way to your eye.

[C_Remington]

Just use box speed and an incident meter and be done with it. As long as your shutter is in working order, and most of your subjects are of average contrast, you'll be fine 99% of the time. Any other adjustments you can make in the print process where all the magic happens anyway.

[Bill Burk]

Like ic-racer hinted, I believe your lowest rating (EI 50) is probably where you should work.

That only one sheet of all four show anything apparent, is the clue. I wouldn't expect to hold 1/3 stop accuracy if your temperature is between 68-75-degrees F.

You could re-do the test, but 50 seems a perfectly reasonable EI result of a Zone System camera test for an ISO 100 film.

[Robert Langham]

A properly exposed silver negative will have all of the information from the exposure- (the actual picture), rendered as silver sitting on, (or in) a base of plastic film. The exposed silver is the image. The base is the base. When you contact print the negative on a #2 grade paper just long enough for the film base to print down to maximum black the tones you see are the actual exposed silver negative. Any meter should have the ISO adjusted until you make negatives that will contact print just long enough to print the base down to maximum black....and have the image of silver visible in its appropriate values.

Some developers give more ISO speed, some less. Some meters have to have the ISO cheated up, some down. It shouldn't be anything too far off the mark or something is amiss. TriX and HP5 run between 200 to 600. FP4 tends to run from 64 to 200. If you get TX at 64 and FP4 at 400....something is not working.

I keep a close eye on meters and exposure. I keep a couple of spot meters and check them against each other regularly. If you WRITE DOWN your exposures you will quickly get to where you know what they are going to be for more situations than you might imagine. The writing down part seems to train your mind quicker.

Map of the South Dike at Shiprock of printed googlemaps taped together.

[aruns]

Hello all,
Thank you for your inputs, really appreciate it.

IC-Racer, Bill, thanks for the leads. I will try to do another set of tests starting from Iso 50 and below.

Remington, as I was explaining to Tim, I started off with incident metering, box iso speed, diafine (no time / temperature constraints)..
After several sheets of film, a few printing sessions, couple other developers, etc. am questioning myself if there's a better way to get negatives that would make printing easier.
Per my understanding, one of the important factors in standardization and exposure predictability is film speed testing (am also working on the others such as contrast control, development time/ temperature control, etc.). that's what led me here.

Robert, Yes, i am working on the "contact printing of the negative on a #2 grade paper just long enough for the film base to print down to maximum black". I some times compare the sekonic meter with my nikon digital meter, and they seem to agree. Thanks for your other inputs too, I will work on the note taking.

Best regards,
Arun

[Sevo]

A properly exposed silver negative will have all of the information from the exposure- (the actual picture), rendered as silver sitting on, (or in) a base of plastic film. The exposed silver is the image. The base is the base.

As far as I understand the ISO (German translated version as per DIN publication) specifications, "base fog" (in the German translation "Grunddichte") is NOT the tint of the plastic base substrate! It would be the cumulated density of the base substrate tint plus any gelatin layers tint and most notably the exposure independent constant fog ("Schleier") across the entire film area. In practical terms, you must zero the densitometer on an unexposed area of the same film. You can't zero it on a area of bare plastics, nor on reference film fixed without development or treated in a different process.

Besides, there is no printing going on in a proper test - the sensitivity is calculated from step wedge exposures measured with a densitometer right on the negative. And "base fog" is not the deepest shadows, but 0.1D beyond it.

[Leigh]

Just use box speed and an incident meter and be done with it. As long as your shutter is in working order, and most of your subjects are of average contrast, you'll be fine 99% of the time. Any other adjustments you can make in the print process where all the magic happens anyway.

Definitely true.

The manufacturers have run more tests than you could in three lifetimes, using accurate laboratory equipment and tightly-controlled processes.

If you find that your results are not "proper", by whatever definition you choose, then you can adjust your processes accordingly.
The trick is to look at real images of real subjects.

As an aside, I can make absolutely no sense of the negatives presented in the original post.
They certainly do not represent a three-stop exposure range, and none of them show an unexposed half-sheet.

- Leigh

[Leigh]

As far as I understand the ISO (German translated version as per DIN publication) specifications, "base fog" (in the German translation "Grunddichte") is NOT the tint of the plastic base substrate! It would be the cumulated density of the base substrate tint plus any gelatin layers tint and most notably the exposure independent constant fog ("Schleier") across the entire film area. In practical terms, you must zero the densitometer on an unexposed area of the same film. You can't zero it on a area of bare plastics, nor on reference film fixed without development or treated in a different process.

That's correct. The "fog" is the result of the developer acting on unexposed emulsion.

It has a measurable density greater than the bare film support (plastic or whatever), but not by much.

- Leigh