F-SAP 1.33 Table f-stop exposure times

Writer and photography / Gerard Smeets

Gerard Smeets shares with us a table with f-stop related exposure times between 1 and 64 minutes plus the manual for this table. The table is also available to download.

Finding the standard exposure time

In many manuals of alternative processes, there is a text like this: ‘make a test strip with 8 times at an interval of 4 minutes, starting with 4 minutes’. So 4, 8, 12, 16, 20, 24, 28, 32 minutes. After the test strip has been developed and dried a time is chosen that is a little bit too dark. Then a second test strip is made. Now with a Stouffer grayscale on the paper. E.g. the Stouffer 31 with 1/3 f-stop.
This is followed by exposure with the previously found – a little too long – time. After that, it will be recalculated. After two test strips and some math, you then have the standard exposure time for your process. Accurate to 1/3 f-stop.

“The f-stop method is as old as photography. The reason it is not used very often in alternative processes is that it is difficult to make the calculations. With this table this obstacle is solved.”

No Stouffer 31 step wedge?

Is it possible to find the standard exposure time up to 1/3 f-stop without a step wedge?
And even better: could it be done with one test strip instead of two?
Yes, and we only need a few things for that.
The recommended start time, the recommended end time, the number of steps, plus a method of exposure at 1/3 f-stop intervals.
f-sap table to 64

1 Start time, end time, number of steps The first lines of this column contain the input data. Start time 4 minutes, end time 32 minutes, 8 steps. To find the f-stop times we use the F-SAP Table. Let’s see if we find the approximate start time and end time in that table. It doesn’t have to be a 100% hit. We start in the left column and if we don’t find them there, search in the columns to the right. The times in columns 1 ¾ and ½ are not suitable. The 4:00 and 32:00 are too close together there.
Going to the right we arrive at column 1/3. There we find the start and end time we are looking for. It’s not 8 but 10 steps. No problem. What’s nice, this 1/3 column runs parallel to the Stouffer 31 grayscale.
It won’t always be such a direct hit. But you have an idea of how the method works. In the table, you can take any time as a starting point and determine the number of steps yourself. Gradually you will discover which column and standard time suits your process best.
The first part of the mission was successful. We found a series of exposure times that give an even grayscale increase.

2Finding a multi-timer It seems complicated with all these different times. Would there be a timer that beeps when the exposure times are reached?
Yes, there are two timers in which we can enter these ten times at once. Without switching the light source on and off each time, a test strip can then be exposed in one operation. The only thing that has to be done at each beep is to PUSH the test strip 1/10 further ON the test strip. 1/10 because we have 10 exposure times here.

Attention: PUSH ON and NOT PULL OFF!

3a Time and date Multi timer With a multi timer it is very easy to apply perfect f-stop exposure times. We have found two free multi timers and will discuss them both. The link https://www.timeanddate.com/timer/ refers to an online timer. Easier than the next one but you must have internet. Go down a little bit until you see the green bar. Click on the time and enter 4:00 minutes.
Then click on Add Timer and enter 5:02.
TimerAnd so you fill in all ten times. If you have them all on the screen, click on Edit for each timer. Set at every timer Buzzer sound. Check if all times are correct and the buzzer is on. You’re ready to test the timer. Click Start. The times run backward and an alarm sounds when one timer has reached zero.
Everything successful? Then click Reset. You’re ready to start exposing the f-stop test strip. Before starting the test, allow the UV light source to warm up. Do not switch it on and off. It should remain lit throughout the test.

3b BARO Multi TimerIf you have an Android smartphone then go to Play Store. Search on the name above. This timer is a bit more challenging than the previous one . One advantage is that you don’t need internet.
Top right: click on icon garbage barrel, OK. This is a reset, only click if you want to delete the times from last time.
Top left 3 horizontal dashes:choose Multi Timer (set only for the first time)
Top left 3 horizontal dashes:
Choose Settings, Alarm duration 3 sec OK, arrow top left
Top left 3 horizontal dashes:
choose Settings, Timer Size choose Small,
arrow top left Bottom right choose +
click on 00:00
In pop up Set Time slide ‘Overtime’ left/off
– enter the time between the lines, OK
– click on + and repeat the above input until you have 10 timers
– check on the screen if all times are correct. Ready? Then click All Start. If the test was successful click on All Reset.
Next time you start Multi Timer click icon garbage barrel only if you do not want to use the exposure times from the previous setting.

More features with the table

The times in the table are useful if your printout is a little too light or a little too dark. In the column 1/2 or 1/3 f-stop you can read the previous or next time. After a while, you get a feeling for the effect of the steps.

There is a possibility that is even more interesting than one step down or up.
Suppose you found a time of 6:21 last time. Today you have another negative and you have made new paper light-sensitive.

With that 6:21 you are in the neighborhood. Let’s look at the table to see if you can find five times that are in the nearby area. We’ll skip the 1/3 column now because we expect our new time to be close to the previous one. Let’s look in the 1/5 f-stop column. Ow! There’s no 6:21 here! No problem, you take a time that’s close. In this case, 6:04.
The table shows five times with 1/5 f-stop interval. First time 4:36, last time 8:00. f-sap table to 8

You want a flying start and are curious how your new negative performs. We therefore skip the test strip from last time.
Instead, cut five strips from your coated paper. You use one for each time and place it under the negative in such a way that the most important parts are exposed. E.g. with the lightest and the darkest parts in the picture. Then expose each strip as a whole with one of the times from the column.
You store them for a moment in a light-tight packaging. Then you develop all five at the same time. You spend one sheet of paper. But you have a treasure of information. Let’s see what we can do with it.
From the five test strips you consider 6:58 as the best exposure time. It wasn’t easy to make that choice. Because the black of 8:00 is deeper. And how you’d like the brilliant white of 4:36. But for most of the print, 6:58 is the best choice.

Wait a minute, there’s gotta be something like dodge and burn, right? Could that be possible with alternative techniques?

Yes, it could. You have all the information you need to do this.
You make a cardboard that is about the size of the part you want lighter. Stick a metal wire on the cardboard so that you can keep the cardboard horizontally in the air.
Then you take another cardboard that is slightly larger than the negative. At the places where more black is needed you make a hole in it.

You enter the three times in the multi timer: 4:36 6:58 and 8:00.

Until the first beep, the whole negative is exposed. After the first beep, you block the light to the lightest spot with the small cardboard. You keep it between light source and negative and move it a little to avoid sharp edges. When the second beep sounds, change the small cardboard for the big cardboard with the hole in it. Keep that at some distance from the negative as well. And this too is moved to avoid sharp borders. The lightest part has 4:36 light, the mid-tones 6:58, and the darkest part through the hole 8:00.
Dodging and burning is a good technique to achieve special results. The old masters of photography used it a lot.

Safety first

Protect your eyes from harmful UV radiation. For example, with strong sunglasses or even better a pair of UV glasses used for sunbeds.

Do not look directly into the light source. Shield the light source from stray light.


Some ultraviolet wavelengths can cause eye damage, e.g. cataract. There is also a relationship between certain UV wavelengths and skin cancer.
Take sufficient measures to protect yourself against this.
Check which wavelengths your UV source emits and whether they are harmful.
The author of this text cannot be held liable for damage caused by UV radiation.

To conclude

There are many ways to do something. Let’s not argue which method is better. In this manual we have chosen to follow a route with f-stopping. These are as old as photography. It is possible to use them with the alternative techniques of exposure for minutes. F-SAP is a method to calculate f-stops for alternative photographic techniques.
Suggestions, reactions, and wishes are welcome. The manual and the accompanying table may be distributed free of charge. Reference may be made to it provided that the source is stated.
Download material and manual:

F-SAP Table f-stop exposure times 1.33

Copyright, all rights reserved. Gerard Smeets BSc, March 26, 2020, gerard@smeets.pro

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