Fstop timing

[monochromeFan]

Been reading on Bruce Tanners website again, stupid idea of f stop timing is actually starting to make sense. Perhaps its just the sleep deprivation.

At least the way bruce tanner describes the process makes it seem very simple.. do a test strip and instead of a linear 2-4,-6 or 5-10-15 second time differenctial sequence. You do it by a scientific "stops". And when you develop the test strip and let it dry you have a strip with far superior differences between each of the stops.

Then you can take your prefered stop number in the test strip and break it down by 1/4 and 1/3 and so forth to get a more accurate and enhanced accuracy versus the old "20 seconds is to dark, 10 is to light, but do i need to break down the 15 second section into 10-11-12-13-14-15 test strip sequence"


But then I hit a wee snag, in times past some of my convential test strips dictated I set the gralab 300 to 5 seconds, and using the dark room automation handy dandy fstop chart..


And doing some quick math, how the hell does a person deal with a 1 or 2 minute, or even 80 minute long expsure time without worring about heat buildup in the negtive itself causing defects?

[Pieter]

Been reading on Bruce Tanners website again, stupid idea of f stop timing is actually starting to make sense. Perhaps its just the sleep deprivation.

At least the way bruce tanner describes the process makes it seem very simple.. do a test strip and instead of a linear 2-4,-6 or 5-10-15 second time differenctial sequence. You do it by a scientific "stops". And when you develop the test strip and let it dry you have a strip with far superior differences between each of the stops.

Then you can take your prefered stop number in the test strip and break it down by 1/4 and 1/3 and so forth to get a more accurate and enhanced accuracy versus the old "20 seconds is to dark, 10 is to light, but do i need to break down the 15 second section into 10-11-12-13-14-15 test strip sequence"


But then I hit a wee snag, in times past some of my convential test strips dictated I set the gralab 300 to 5 seconds, and using the dark room automation handy dandy fstop chart..


And doing some quick math, how the hell does a person deal with a 1 or 2 minute, or even 80 minute long expsure time without worring about heat buildup in the negtive itself causing defects?
When would you need such an exposure time?

[monochromeFan]

Full Stop 5 10 20 40 80
+1/4 5.9 11.9 23.8 47.6 95.2
+1/2 7.1 14.1 28.3 56.6 113.2
+3/4 8.4 16.8 33.6 67.3 134.6
F-stop Timings with 1/4 stops

thats supposed to come from Nocons's book.. SO as a result if i start out making a f/8 @ 5 second print of an orange on 4x6 enlarging paper things can tend to get long and lenghty when you try to do an 8x10 or 11x14 print.

[esearing]

if heat from your enlarger is a problem you will want a different head. for 4x5 I also prefer the beseler glassed carriers to keep the negatives flat. Most of my 11x14 exposures on warmtone papers run near the 1 minute mark for exposure. But I also use the RHDesigns Analyzer which breaks down exposure into 1/6 or 1/12 stop increments and has an easel light meter to give me the starting times. Even if I could print in 5 seconds I would likely stop down my lens to slow it to 10 or 20 seconds for dodging/burning.

[jnantz]

im always amazed at how overly complicated people make a very simple process.
80 minute long exposures ?
they use a different light source
and modify their developing methodology so they don't need
a 1 hour 20 minute exposure ...

[notorius]

Well I dealt with longer times with no problem. 1 - 2 mintes exposure( Fomatone paper), 100W incandescent light bulb. There is an IR filtr between the light source and the film carrier. And I always use AN glass. I would definitely use LED technology these days.
How many prints have you done so far? And what are the real issues you need to solve in the process? It seems form the many posts you have started, that you are (over)prepared.

[paulbarden]

It looks to me like you're investigating theoretical problems that you will almost certainly never encounter in practice. The odds of you ever needing an 80 minute exposure to make a print is practically zero.

The only time in which I had to deal with a LONG exposure was one instance in my professional career as a darkroom-technician-for-hire, working for a well-known Canadian artist. We had to make 2.5 X 8 foot prints from 35mm negatives, using a Beseler 23C II enlarger. Exposures were between twenty and forty-five minutes long. There were no unusual technical challenges to the process - it was just a bit tedious. Yes, the lamp heated things up during the exposure, but that only meant that we had to pre-warm the enlarger for a couple of minutes to properly warm the negative, so that it didn't "pop" during the exposure (causing a focus shift). It was easy to avoid the problem.

You're fussing over scenarios you're unlikely to ever encounter. Just get on with it.


im always amazed at how overly complicated people make a very simple process.

Basically, yes. Some people love to throw obstacles in their path, so they have something to worry about. Some of us just get on with the work with as little fuss as possible.

[Doremus Scudder]

I think we're talking about an 80 second exposure here, not 80 minutes, which is not all that uncommon with larger prints (still long, though).

Monochromefan,

F-stop timing really works better with and f-stop timer, which has settings in stops and fractions of stops. Otherwise, you need to use the conversion charts.

If you want the logical spacing of f-stop timing without the timer or the conversion chart, just use percentages. That's what I do. Test strips are usually in 30% intervals (I don't think you'd get useful information from a test strip in full stops or 100% intervals; the spacing between exposures is just too great).

I like exposures in the 15-30+ second range. I time with a metronome and count seconds, so I make test strips by sequentially covering stripes of the test strip after an initial base exposure. My (approximate) 30% test has these final exposures: 10 sec., 13 sec., 17., sec., 22 sec., 29 sec., 38 sec. That means I start the exposure, count 10 seconds and cover the first stripe, count 3 seconds, cover the next, etc. The counting sequence is easy to remember after a time or two: 10 - 3 - 4 - 5 - 7 - 9.

If that's not enough exposure, then I'll open up a stop or adjust the light intensity and make another test strip. I'd only use base exposures longer than 40 seconds or so If the print were really large and needed longer exposures or if the negative were really dense and I didn't have enough light, even only closed down one stop. In that case, I simply double the strip timing to 20 - 26 - 34 - 44 - 58 - 76 (count: 20 - 6 - 8 - 10 - 14 - 18).

When printing, make exposure adjustments as you need and dodge and burn as needed, but think in percentages of the base exposure (e.g., dodge 10% here, burn 70% there, etc.). After a while, you get a pretty good idea of how much x% exposure change makes. Keep in mind, however, that all this is contrast-grade dependent (even with f-stop timing). A 2/3-stop increase in exposure is about that same as adding 70%, but that much extra exposure makes a smaller change in print density at grade/contrast setting #1 than at grade/contrast setting #4.

Keeping track of print manipulations in percentages is helpful when you make a different size print. Once you establish the base exposure for the new print size, you can then easily figure the timing of dodges and burns, which should get you in the ballpark (I find that different-size prints often need a bit different treatment, so those times are always just a starting point for me).

Hope this helps,

Doremus

[Peter Lewin]

A quick thank-you to Doremus, who is one of the most reliable and helpful members of this forum. I've been printing for around 50 years, so I'm not a novice, and I still learn new ideas from his posts, in this case about his test strips. I always made mine as I was taught by Fred Picker, setting my timer for 2 or 3 seconds, and making strips straight across, getting for example, 3,6,9,12,15 seconds, which were not always as easy to read as I would like. So yesterday I tried Doremus's approach. In Excel, I made a simple spread sheet. For the top section, I made rows from 4 seconds to 10 seconds, and going across, each column was 30% longer than the one to its left. Then below I changed the formula so that keeping the first column of seconds, each column now showed just the difference from the column to its left, so I had a number of sequences similar to the ones Doremus mentioned (for example I had one which I think - my cheat sheet is down in my darkroom - went something like 4 second base, then 2,2,3,3,4,6). Worked very nicely! And since I have an idea of final exposures for different format negatives and enlargement sizes, I can simply pick a row (sequence) which puts my "expected" exposure near the middle, and use the test strip to fine tune.

[Doremus Scudder]

A quick thank-you to Doremus, who is one of the most reliable and helpful members of this forum. ...

Thanks Peter!

Glad you found the percentage method helpful. FWIW, I've standardized on just one sequence at 30% intervals (25% works too, but I've found that 30% is not too wide to be able to interpolate intermediate values closely enough - I do quite a bit of exposure tweaking once I get to making full-size prints anyway). I've got my test-strip sequence taped to the wall by the enlarger, writ large in sharpie so I can refresh my memory if needed.

If I find I need longer or shorter than 10 seconds or longer than my usual 38 seconds, I'll just add a few intervals on either end. It's just a tiny bit harder to figure going down in time rather than up and keep the same interval. I just multiply by 0.77 (not the 0.7 that you'd think would work).

So, the intervals below 10 would be, in descending order: 10 - 8 - 6 - 5 - 4. Easy to remember. I have all these written in on my taped-up reminder too, so I can just start where I want in the sequence. Normally, I'll start at 10, but if there are special circumstances, I'll pick a lower number.

On the other end, it goes 38 - 50 - 65... that's enough! And, as I mentioned above, you can always pick a spot to start and just double the times and counting and get really long times if needed.

Just for clarity, my reminder sheet looks like this (bold type is the "core" sequence):

Time : 4 - 5 - 6 - 8 - 10 - 13 - 17 - 22 - 29 - 38 - 50 - 65
Count: 4 - 1 - 1 - 2 -- 2 -- 3 -- 4 -- 5 -- 7 --- 9 - 12 - 15

I can just start anywhere in the sequence and end anywhere too.

Best,

Doremus

[Tim Meisburger]

For test strips, I normally use 8 seconds, 11, 16, 23, and 32, mimicking the f stops on the lens. That means if I have a 23 second exposure and want to make it 32 seconds for more time for dodging and burning, I just close down the lens one stop. I also have a chart on the wall with full stops, half stops, third stops and quarter stops, in case I want to dial it in. If I want to make a larger print, I can map the exposure in stops.

[monochromeFan]

For test strips, I normally use 8 seconds, 11, 16, 23, and 32, mimicking the f stops on the lens. That means if I have a 23 second exposure and want to make it 32 seconds for more time for dodging and burning, I just close down the lens one stop. I also have a chart on the wall with full stops, half stops, third stops and quarter stops, in case I want to dial it in. If I want to make a larger print, I can map the exposure in stops.

How do you know that is the correct method to use to deduce the correct time? What about contrast filters being used..

[Pieter]

How do you know that is the correct method to use to deduce the correct time? What about contrast filters being used..
That is what test strips are for, usually made with a #2 filter. And if you make the leap to split-grade printing, you don't need to determine the grade, either.

[Conrad . Marvin]

F-stop timing has saved me lots of time over the years. I have an RH Designs Vario f-stop timer which can be used for split printing because it has two channels. I have been able to set up the basic and burning exposures on a small print in both channels, then make a change in the basic exposure for a larger or smaller print and the timer corrects the burning exposures automatically. The resulting print is usually very close. Saves time and money and works great with cold light heads that vary in brightness over a longer exposure since it has a sensor which can detect the light source changes and correct the time. Good stuff, but not easy to get because it comes from the UK.

[Doremus Scudder]

For test strips, I normally use 8 seconds, 11, 16, 23, and 32, mimicking the f stops on the lens. That means if I have a 23 second exposure and want to make it 32 seconds for more time for dodging and burning, I just close down the lens one stop. I also have a chart on the wall with full stops, half stops, third stops and quarter stops, in case I want to dial it in. If I want to make a larger print, I can map the exposure in stops.

Let's see... opening the aperture one stop doubles the amount of light hitting the paper. Decreasing it on stop halves the light hitting the paper.

Therefore, closing one stop would require twice the exposure time to compensate for the halving of the intensity. So, your 23-second exposure should become 46 seconds if you close the aperture one stop.

Due to the inverse square law, the amount you have to open the aperture to double the light is subject to a factor of the square root of 2. Time, on the other hand, follows simple doublings and halvings to get a stop difference.

So, you can think of your time sequence, 8, 11, 16, 22, 32, 45... as half-stop intervals, not full-stop intervals. Apertures on the lens, 8, 11, 16, ..., however, are full stops.

Best,

Doremus

[monochromeFan]

Let's see... opening the aperture one stop doubles the amount of light hitting the paper. Decreasing it on stop halves the light hitting the paper.

Therefore, closing one stop would require twice the exposure time to compensate for the halving of the intensity. So, your 23-second exposure should become 46 seconds if you close the aperture one stop.

Due to the inverse square law, the amount you have to open the aperture to double the light is subject to a factor of the square root of 2. Time, on the other hand, follows simple doublings and halvings to get a stop difference.

So, you can think of your time sequence, 8, 11, 16, 22, 32, 45... as half-stop intervals, not full-stop intervals. Apertures on the lens, 8, 11, 16, ..., however, are full stops.

Best,

Doremus

Still doesnt make much sense.. what about my wee little omegaron 50mm lense thats 3.5 4 5.6 8 11 16 on the aperture dial

[Pieter]

Still doesnt make much sense.. what about my wee little omegaron 50mm lense thats 3.5 4 5.6 8 11 16 on the aperture dial

A stop is a stop, no matter the lens. Just remember 3.5 is a half-stop faster than 4. But the ensuing stops are a full stop apart.

[Jim Jones]

Still doesnt make much sense.. what about my wee little omegaron 50mm lense thats 3.5 4 5.6 8 11 16 on the aperture dial

Except for f/3.5, the aperture numbers on your (and almost every other) lens increase or decrease by the square root of 2. In the past, several other systems have been used, although our present system seems the most logical in practical use once we become familiar with it. While f/2.8 would have been a logical stop instead of f/3.5, perhaps opening up that extra fraction of a stop would have resulted in images that someone decided was not sharp enough with that particular lens. Since that sequence of numbers is familiar to most photographers, f-stop timing is logical for us. It's a personal matter. It may seem desirable to vary the aperture to bracket the exposure, but many lenses have a narrow range of apertures that render adequate sharp images. Your modestly priced Omegaron should be stopped down a stop or two for best sharpness, but not much, if any, more because diffraction will then degrade the image. Even with a better enlarging lens, I like to stop down at least one stop after focusing to help cover sloppy focusing, enlarger misalignment, and film curvature.

[Doremus Scudder]

Still doesnt make much sense.. what about my wee little omegaron 50mm lense thats 3.5 4 5.6 8 11 16 on the aperture dial

Apertures nowadays are marked in f-numbers. The "f" stands for "focal length." These numbers are always given as fractions of the focal length of the lens. f/8, therefore, means that the optical diameter of the aperture is 1/8 the focal length of the lens. The beauty of the system is that the same amount of light gets through a 200mm lens at f/8 as a 100mm or a 50mm lens at f/8 (assuming the same exposure time, of course).

The aperture sequence is based on a doubling of the light intensity for each stop. Because of a quirk of physics :), the pesky inverse square law, doubling the aperture diameter gives 4x the light intensity. To get just twice the intensity, the aperture needs to be changed by a factor of the square root of 2 (approx. 1.414). So, multiply, say 8 by 1.414 and you get 11.3, etc. (I did say approximate), on up the scale.

The f-stop sequence in their common full stops: 1.4 - 2 - 2.8 - 4 - 5.6 - 8 - 11 - 16 - 22 - 32 - 45 - 64 - 90 - 128 (that should cover just about any LF lens.) Numbers in between are fractional stops. You can find a ton more info at: https://en.wikipedia.org/wiki/F-number

Shutter speeds are a lot simpler: double the time, double the light intensity. Want one stop more than 10 seconds? That'd be 20 seconds.

Working these two things together: Close the aperture one stop, double the time to keep the same exposure. Open one stop: halve the time to keep the same exposure.

Many lenses that open a bit wider than full-stop f-numbers have maximum apertures that don't agree with the full-stop sequence. Hence your f/3.5 on the Omegaron and the f/7.7 on my 203mm Ektar, etc., etc.

F-stop timing for enlarging simply uses the unit of a "stop," i.e., the doubling or halving of the light intensity as a basic unit. The increments are then divided further into halves, thirds, sixths or even 12ths of a stop. The problem is, calculating the intermediate values requires the use of fractional exponents (see here: https://www.largeformatphotography.info/forum/showthread.php?7894-f-stop-timing-and-partial-stop-calculation posts #6 and #7).

I prefer percentages, which has the same advantage, but is easier to figure in my head and without a chart. Even Ralph Lambrecht, an exponent of f-stop timing, gives the percentages for fractions of a stop in his chapter on f-stop timing in his book, "Way Beyond Monochrome":

"For normal paper grades, between grade 2 and 3, enlarging time differences of a 1/3 stop (~20%) are significant in tonal value, 1/6 stop (~10%) can easily be seen and differences of a 1/12 stop (~5%) are minute, but still clearly visible, if viewed next to each other. Smaller increments may be of use for paper grades 4 and 5..."

Check out the whole chapter here: https://www.tmax100.com/photo/pdf/fstoptiming.pdf

Clearer now?

Doremus

[Bob Wagner]

Buy an F stop primer, you'll never look back

[Alan Townsend]

Been reading on Bruce Tanners website again, stupid idea of f stop timing is actually starting to make sense. Perhaps its just the sleep deprivation.

At least the way bruce tanner describes the process makes it seem very simple.. do a test strip and instead of a linear 2-4,-6 or 5-10-15 second time differenctial sequence. You do it by a scientific "stops". And when you develop the test strip and let it dry you have a strip with far superior differences between each of the stops.

Then you can take your prefered stop number in the test strip and break it down by 1/4 and 1/3 and so forth to get a more accurate and enhanced accuracy versus the old "20 seconds is to dark, 10 is to light, but do i need to break down the 15 second section into 10-11-12-13-14-15 test strip sequence"


But then I hit a wee snag, in times past some of my convential test strips dictated I set the gralab 300 to 5 seconds, and using the dark room automation handy dandy fstop chart..


And doing some quick math, how the hell does a person deal with a 1 or 2 minute, or even 80 minute long expsure time without worring about heat buildup in the negtive itself causing defects?

Mono,

To deal with heat effects, replace tungsten with LED bulbs if possible.

Get some neutral density filters to lengthen exposure if needed to replace fractional seconds with even seconds.

Or spend big bucks on an fstop timer that you don't really need otherwise.

Alan Townsend

[flamberge]

Hi.

I think this is my first post here, and for the fist time IMHO I may be able to contribute something.

please forgive my english, I was raised speaking spanish and german.

I have been using the f-stop method for my enlarging from some 10 years ago, and I will try to explain some misunderstandings.

If a good print takes some 28 seconds of exposure, it doesn’t matter if you calculate it in f-stops or seconds. The final exposure will always be the same 28 seconds.

There is no way that using the f-stop method will take you to 80 plus seconds exposure times.

What the f-stop method gives you, is a more rational way of thinking about increasing/decreasing a given exposure time because the increment in density (within limits) of the paper picture is ruled by the same law of physics as the exposure of a negative. In simple, is’t just not linear.

so, if you have a given density achieved at an exposure of 4 seconds, and now you want to double it, the time you will need to do it will be 8 seconds.

But if the same density was achieved at an exposure of 16 seconds, now you will need 32 seconds of exposure to double the density of your print.

A test strip exposed in linear increments of the same amount of time ( say, 5 seconds), will lead to a decreasing difference in density between exposures as time goes on.

That’s why the linear method of thinking exposure fails. Sure, you can get perfect prints that way, (I did it for almost 40 years) but it takes longer and is not as intuitive as the f-stop method, who in its roots is the same way as we expose negatives.

You get a lot more meaningful increments in density using f-stops.

During the pandemic I was sent home. Im a pediatric surgeon with a history of a mild hearth attack. I spent my time among other things, to my hobby in electronics. I designed and made an arduino f-stop timer , You can see it (in spanish) in the spanish Nikonistas forum, here: https://www.nikonistas.com/digital/foro/topic/480244-f-stop-timer-para-ampliadora/

[Renato Tonelli]

Flamberge: excellent explanation. Your f-stop timer looks great.

Welcome to the Forum.

[ic-racer]

You can easily get into really long exposure times with f-stop timing. For example if you need to increase a one-second exposure by 60 stops, your exposure will be longer than the estimated history of the universe.

log2(436117076600000000 (https://81018.com/universeclock/)) = 58

[Vaughn]

One way is just as good as another way. There is nothing that makes one method 'superior' or "more intuitive" than the other...other than how the individual wants to think about it and what they are use to.

Thankfully my exposure unit has no f/stops so it is a non-issue for me.

[aduncanson]

I found Darkroom Automation's f-stop dial for the graylab timers to be very helpful.

https://www.darkroomautomation.com/support/grastops.pdf

[Pieter]

One way is just as good as another way. There is nothing that makes one method 'superior' or "more intuitive" than the other...other than how the individual wants to think about it and what they are use to.

Thankfully my exposure unit has no f/stops so it is a non-issue for me.

We already think in terms of f-stops for exposure, so doing the same for printing is more intuitive for me. Plus, it is about a stop difference moving from 8x10 to 11x14, all my times including dodging and burning can be easily applied without starting over.

[Vaughn]

We already think in terms of f-stops for exposure, so doing the same for printing is more intuitive for me. Plus, it is about a stop difference moving from 8x10 to 11x14, all my times including dodging and burning can be easily applied without starting over.

That's cool...and, right, wrong, or otherwise, working in seconds is intuitive for me (back in my silver printing days).

As an aside, I would rarely have a goal of making a 16x20 print to look just like an 8x10 print from the same negative. I tended to see them as two different images...considering how print size can affect our viewing of an image. I preferred 'starting over'...:cool:...plus my method of burning/dodging was too complicated (too crazy perhaps) to keep track of and record.

[nolindan]

... plus my method of burning/dodging was too complicated (too crazy perhaps) ...

You like "Crazy complicated"? - why you are just the man for f-stop printing with all of its accoutrements.

Well, maybe not, it does have the danger of simplifying things for some people. They find "sanely simplified" to be just too boring for words, and, after all, it can become a trap that is hard to escape from.

[Vaughn]

You like "Crazy complicated"? - why you are just the man for f-stop printing with all of its accoutrements.......

Most likely! :cool:

Instead of any significant dodging, I made the base exposure a little light, then burnt the print down selectively until I saw what I wanted. I used the base exposure to burn in areas with a hole in a piece of cardboard. An area of the image might get burned in by hitting the timer hit 4 times with the hole this size, moved this way...and so forth. I'd look at the wet print and might decide to give that area 5 hits, but move the hole this way this time. The timer might get hit 30 or more times before I am done. Chiseling away with light. Lots of fun, especially having so much space to work with making 16x20s.

This is a ~7x16 silver gelatin print from 4x5. Actually - not a great reproduction of the print, but a lot of fun working with it.

[flamberge]

You can easily get into really long exposure times with f-stop timing. For example if you need to increase a one-second exposure by 60 stops, your exposure will be longer than the estimated history of the universe.

log2(436117076600000000 (https://81018.com/universeclock/)) = 58

Hi

I said in my previous post the increase in densitiy with longer exposures is "within limits". The point is, it doesn't matter if you mesure in seconds or f-stops. There will be some point in exposure time where you get the maximum density the paper is capable to achieve. There will be no more silver in the paper to be converted. After that, any longer exposure time is a waste of time.

And IMHO for getting maximum densities, at least with current chemistry and available photo papers, the amout of time involved I think is a little shorter than the estimated history of the universe.

kind regards

[Maris Rusis]

Back when I printed for others speed of production and efficient use of paper was the key to productivity and $. And f-stop timing was never part of it - too slow.

Because of always working in the same darkroom with the same enlarger and the same paper easel I could just look at the projected image and have a very good idea of the required print exposure. This came easily after only a few hundred expose, develop, fix, and look cycles. Doesn't this happen to other people?

An example: If I figure the print exposure is about 8 seconds I'll line up a long test strip that samples the thinnest and densest part of the projected negative together with a selection of mid-tones. Then with my foot-switch activated timer set to 2 seconds I make exposures 2-4-6-8-10-12-14 seconds. The test strip will be too light at one end and too dark at the other end so the correct exposure must lie between. Because I sampled thin and dense parts of the negative I also have information about possible burning and dodging. Suppose the correct exposure is 9 seconds I'll tap the foot-switch 4 times to get to 8 seconds then close the lens 1 stop and tap the foot-switch one more time to get to 9 seconds. Aha, f-stops do get involved!

[Vaughn]

Makes sense, Maris. There's a bit of art (or at least common sense) that goes into a proper test strip...which for me means big enough to be useful, and placed where one gets the most useful information about the whole image.

I made a full size work print from the results of the test strip. It did not have to be right-on. I could study it, make any minor changes in exposure and start making decisions for how to work with the image (mostly burning).

[jnantz]

I 've found just closing fstop down 3 clicks and doing a test strip, and if I am doing multiple prints from exposures that all around the same density, &c, I've been fortunate enough to know how to guesstimate the exposure pretty well ... for me at least test strips are not too hard and just easy enough for me to screw it up from time to time.

[flamberge]

Suppose the correct exposure is 9 seconds I'll tap the foot-switch 4 times to get to 8 seconds then close the lens 1 stop and tap the foot-switch one more time to get to 9 seconds. Aha, f-stops do get involved!

Indeed, that's the other way of using the f-stop method. In fact, it's the real one. The problem is, most enlarging lenses have AFAIK full or at most 1/2 f-stops increments.

Using seconds allows you to choose full, 1/2, 1/3, 1/4 (or whatever) f-stops progressions. Better fine tuning.

[Doremus Scudder]

The whole point of moving away from a test strip made in equal intervals is to avoid the unevenness of exposure in the sequence of stripes. With a set time increment, that the amount of density change with each subsequent stripe progressively decreases. If you make a test strip in two-second intervals, the second stripe will be twice the original exposure, the third will be only about 1.5 times the previous exposure, the fourth only 1.25 times the previous exposure, and so forth.

This makes the actual exposure difference between stripes uneven and makes telling them apart at the far end of the scale rather difficult (I remember strips where I couldn't fine the "line" between exposures; simply too close together).

While I agree that f-stop timing is too fiddly, both f-stop timing or using percentages (as I do) fixes this problem. I prefer percentages because it is faster and more even than both f-stop timing and just using even increments to make a test strip.

But the usefulness doesn't stop there. Recording burning, dodging and split-grade exposures in percentages of a base exposure really help when making a different-size print or a print on different paper with a different speed. Once the base exposure is found for the new print, one can get very close to the right manipulations by just re-calculating their times from the base exposure using the percentages. Again - faster.

All the methods work; it's just a matter of streamlining things and using what seems most intuitive and practical for you.

Best,

Doremus