Determining ISO of your emulsion

Could be. I have Henney and Dudley's Handbook of Photography where they describe how to determine development time for desired gamma.

Nodda Duma said:

Dark slide is the term I was looking for (sorry had a brain fart). It looks like a dark slide with a 3.5" X 0.5" sized rectangular hole cut into it.

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Maybe you made a set of 7 of them, each with a different slot?

Er...

I must admit some embarrassment and a sudden realization why the early test where I used my dark slide contraption had such odd results. Fortunately I tossed that data.

Overthinking can be very humbling sometimes.

Let's not dwell on it much longer..



I think I'd have to slide one in from the opposite to block the light path same time as I slide the modified on out.

Nodda Duma said:

I've sourced a Kodak No. 21 Photographic Step Tablet so I can at least estimate D values until I find a suitable densitometer.

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You can tape that onto a plate in contact, and expose the plate to an evenly lit flat-toned subject through it... You could do a contact exposure in a darkroom instead of in-camera, there are many ways to make a home-made "Sensitometer" with a Step Tablet.

These step tablets are available for about the price of a roll of film. Calibrated step tablets can be had for about the price of three rolls of film. This low cost for such an important tool should be stressed more often, because a step tablet can pay for itself the first time you use it.

Nodda Duma said:

Here's a strip sample with associated exposure times. After all my talk about cutting holes in dark slides, I couldn't find the dang thing when I took this shot.

I selected the 6s strip as the most balanced, understanding that vegetation should be slightly darker.

View attachment 160059.

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OK perfect thin lines separating the test exposures: impossible with a home-rigged gadget. I bet you pulled the darkslide "out" one section every 2 seconds and then every second near the end. Then you "drew" lines later to show the strips more clearly.

If you do this in "one pass" without closing the shutter, then you will avoid intermittency effects. Then I might suggest a logarithmic series such as 64 seconds, 32, 16, 8, 4, 2, 1.

To achieve that series you will start a 64 second timer and choose to move the slide at the difference... so pull a section open and pull a section at a time as your elapsed time reaches 32, 16, 8, 4, 2, 1 and 1 second.

This will give you a single time-based sensitometric series of: 64 seconds (32 + 16 + 8 4 2 1 1), 32 seconds ( 16 + 8 4 2 1 1), 16 seconds (8 4 2 1 1), 8 seconds (4 2 1 1), 4 seconds (2 1 1), 2 seconds (1 +1 ) and 1 second. If you leave the very last segment uncovered it can be where you measure base + fog.

You could use the visually best section to base your exposure (after all we are talking about an equivalent exposure index to use "today"), or...

If you can shoot a flat tone subject or at least organize the test shot to have something in view that has a single tone across the scene big enough to meter and measure on the plate later... you will get more information.

It might feel right to start with the dark slide almost all the way out and push in about 3/8 inch at a time... (I don't think there is any consequential difference in the result but this seems more likely to feel right).

To achieve that series you will start a 64 second timer and move the dark slide at the appointed times... so pull the darkslide all the way out and start pushing it in 3/8 inches and push a section at a time after you count seconds 1, 1, 2, 4, 8, 16, 32.

Bill I ended up doing something very similar to what you suggested in that last thread, and generated a printout of a table which gives me exposure times for measured EV (EV100) and f/# setting.

So all the trials and tribulations of the weekend paid off. Once I was satisfied I knew what my emulsion was doing, I called a friend and arranged to take dry plate photographs of the Brookline, NH fire department's engines prior to the Independence Day parade. Engines No. 2 and No. 3 date to 1929 and 1939, respectively (the 1919 engine didn't start so it couldn't be pulled out of the station), and they were kind enough to park them behind the station prior to the parade. With all my fingers crossed and sweating bullets as I worked in my darkroom, the negatives.... came out perfect! Well, just a little thin as expected but good enough to make prints from. See my recent media posts.

Thanks fellas, I appreciate the help and letting me bounce ideas off you all!

Regards,
Jason