The Test Strip - a quick quote from Lootens

[MattKing]

That's an interesting thought. So, for argument sake lets take the following sequence . . . 5, 10, 15, 20, 25, 30, 35, 40. Lets assume in this case the closest patch that matches your desired exposure is around 25 seconds. So, you compare the 20 second patch to the 25 second patch, and you compare the 30 second patch to the 25 second patch. Are the patches on each side of the 25 second patch not located plus and minus 1/4 of a stop? I feel compelled to ask these silly questions to fill in the gaps in my grey matter. ;-)

Nope, because stops are logarithmic, not arithmetic.

The following sequence of times is quite close to a one-half stop sequence: 8, 11, 16, 22, 32, 45, 64 - they look quite familiar, don't they.

If you square each of those numbers, you will see another type of progression.

Going back to your original sequence, if you square those numbers, you will get a reliable indication of how their densities might appear to progress -

25, 100, 225, 400, 625, 900, 1225, 1600 -I've added the bolding to help show the correspondence.

 

[Bill Burk]

Make enough prints and i think you will find that the teststrip will eventually be out of your workflow.

Now, if i humbly could ask a couple of questions. Who is Lootens and what size do you make your teststrips in? Full printframe or a strip torn off a sheet?

No, not arrogant. You took up a respectful contrary position. I don't plan to do away with test strips. On the contrary - here I'm planning to use them more.

The book I'm referring to is... Lootens on Photographic Enlarging and Print Quality, by J. Ghislain Lootens F.P.S.A., F.R.P.S. 1944

I have a big pair of scissors I use to cut a sheet of 11x14 paper into 5 or 6, 11-inch strips. I have an 8x10 paper safe and I keep these strips at an angle on the shelves (Grade 2 paper on second shelf, Grade 3 on third shelf).

I start the timer with the strip uncovered - the whole strip gets a random amount of starting time. Then I cover all but a 1/2 inch x 11 inch and start counting clicks. These are the ticks I count which are third-stops down from 40 seconds... (8 - 7 - 5 - 4 - 3). After each interval, I move the cardboard about a half inch until the whole strip is uncovered and receives the remaining time on the timer.

 

[DannL.]

Nope, because stops are logarithmic, not arithmetic.

The following sequence of times is quite close to a one-half stop sequence: 8, 11, 16, 22, 32, 45, 64 - they look quite familiar, don't they.

If you square each of those numbers, you will see another type of progression.

Going back to your original sequence, if you square those numbers, you will get a reliable indication of how their densities might appear to progress -

25, 100, 225, 400, 625, 900, 1225, 1600 -I've added the bolding to help show the correspondence.

I can see what you're saying. So, increasing the time on a timer from 5 seconds to 10 seconds for example is not actually doubling the exposure. That being the case, what is the increase in exposure in that example?

 

[Bill Burk]

5 to 10 is double. But then 20 is double 10.

You'll have the book soon enough and the examples will help illustrate.

While the advantage of making test strips in f/stop series is real... It's really not THAT big a deal. After all, it was good enough for Ansel Adams to count 5 second intervals.

The bigger lesson to take from Lootens is to throw in a step exposure of 80 seconds.

 

[pdeeh]

This is an interesting and informative thread, and I'm glad Bill started it.

The first - only - book on enlarging I've read is Nocon's "Photographic Printing", and having read it, I promptly forgot everything he had to say about using f/stops for test strips. Accordingly I've been doing 4-8-12-16-20 sequences; now as DannL implied above, if it gets you to the right exposure, it doesn't matter much how you got there.

Nevertheless I've got my Nocon out again and will have a go. It does seem slightly mad that while I understand perfectly the reciprocal relationship between exposure and f/stop when I'm taking photographs, I haven't been able to carry it into the darkroom ...

At the risk of appearing extremely dim, though, one thing I really don't get is this:

I start the timer with the strip uncovered - the whole strip gets a random amount of starting time. Then I cover all but a 1/2 inch x 11 inch and start counting clicks

If you look at your strip and say "Ah! 8 seconds is just right!", how is the random exposure time accounted for?

 

[DannL.]

I will withhold critical judgment on the f-stop thingy until I've had a chance to study this again. I looked into this years ago and ran the other way. But now that I'm older . . . I can't run like that. Meantime I found the following doc, and I'm reading it intensely.

TimingExposureEd2.pdf

One problem I might have, and as it typically goes, if the base exposure of 20 seconds is correct for this series of negatives/paper, how to build a strip around that figure in f-stop times. ie; 15, 17.5, 20, 22.5, 25 is an easy sequence to calculate on the fly. An accuracy of plus or minus 1/2 second would be pushing it with my timer. When compared to the chart with "base exposures" in the document above, the differences in exposure times are slight.

 

[Doremus Scudder]

I prefer to use a simple percentage progression.

This works in exactly the same way as f-stop timing (i.e., you get the same amount of density change between each strip) but does away with the logs, the decimals and thirds of anything.

A 30% test strip might go like this (in seconds): 10, 13, 17 (rounded from 16.9), 22 (rounded from 22.1), 29 (rounded from 28.6), 37, 48.

Since I use a metronome to print, It is simply a matter of counting: 10 - 3 - 4 - 5 - 7 - 9 - 11 - off.
The values are rounded, but very close to 30%.

I determine my basic exposure from a highlight value and then start to make test prints. If I need to change contrast much (i.e., change graded paper grades or more than a few cc for VC paper on the dichro head) then I'll make a new test strip.

Contrary to how others work, I find a test strip to be invaluable and economical.

Best,

Doremus

 

[pentaxuser]

A benefit as I understand it from the fstop method is that if say 4 secs in right for the basic exposure but 2 more strips at say 1/3rd stop more each is right for the sky then if you switch to bigger or smaller paper then once you calculate the correct basic exposure from the change in projection size then the sky will still be 2/3rds of a stop more so no need to re-calculate all the different exposures on the print

It clearly helps if you have an fstop timer but Ralph Lambrecht's fstop table gives you the times in secs

pentaxuser

 

[Bill Burk]

I start the timer with the strip uncovered - the whole strip gets a random amount of starting time. Then I cover all but a 1/2 inch x 11 inch and start counting clicks. These are the ticks I count which are third-stops down from 40 seconds... (8 - 7 - 5 - 4 - 3). After each interval, I move the cardboard about a half inch until the whole strip is uncovered and receives the remaining time on the timer.

All the paper is uncovered for 40 seconds, the next longest time is 40 - 8 = 32 seconds, the next strip is 40 - 15 = 25 seconds and so on. It shouldn't matter which seconds I choose to take away (beginning, middle or end), but I give a few seconds for lamp warm-up time in my system.

 

[Doremus Scudder]

A benefit as I understand it from the fstop method is that if say 4 secs in right for the basic exposure but 2 more strips at say 1/3rd stop more each is right for the sky then if you switch to bigger or smaller paper then once you calculate the correct basic exposure from the change in projection size then the sky will still be 2/3rds of a stop more so no need to re-calculate all the different exposures on the print

It clearly helps if you have an fstop timer but Ralph Lambrecht's fstop table gives you the times in secs

pentaxuser

This relationship works with percentage timing also. Plus all dodging and burning can be recorded as percentages of the basic exposure time as well, which seems to me to be rather more complicated with f-stop timing (I can't figure out how to wave a dodging wand around for 2/3-stop..., I like to just count seconds with my metronome).

When I scale a print up or down, I find the basic exposure using a test strip (as described above) and then make a pilot print with the manipulations I've recorded adjusted for the new print size as percentages of the basic exposure time. This is a good starting point for printing at a new size.

Best,

Doremus

 

[Bill Burk]

Doremus,

I think percentage timing is mathematically the same as f/stop timing... Look at your counts and mine... They're identical! I call mine 1/3 stop and you call yours 30%

 

[DannL.]

I received the Lootens book and scanned through it. It was definitely worth the investment. I found it interesting how this book complements the "The Craft of Photography" by David Vestal, another book I had recently acquired.

 

[Bob Carnie]

Would it not be the same at lets say 10 seconds... but if you go up in printing time I think 1/3 stop will change the density more than a 30% change.

base your time at 100 seconds , changing 1/3 stop will look the same as lets say 70 seconds??? You are now into reciprocity failure.Yes?No

Doremus,

I think percentage timing is mathematically the same as f/stop timing... Look at your counts and mine... They're identical! I call mine 1/3 stop and you call yours 30%

 

[Bill Burk]

I don't know, I didn't really double-check the math.

The next numbers of seconds in third-stops according to an old Master light meter, 40 - 50 - 64 - 80 - 100

Reciprocity failure is a factor to keep in mind.

I also believe the idea that you get consistent steps using f/stop printing breaks down a little when you change paper grades.

Because 1/3 stop "change" at Grade 2 is a gentle difference... While it's a rather dramatic difference at Grade 4.

Still I'd prefer f/stop differences than 5 - 10 - 15 - 20 - 25

p.s. I made the 11x14 print last night using Looten's 5 - 10 - 20 - 40 - 80, and it sort of caught me off guard. The vintage neg was kind of thin compared to my usual. I had to use f/22 to make that test strip.

 

[Doremus Scudder]

Doremus,

I think percentage timing is mathematically the same as f/stop timing... Look at your counts and mine... They're identical! I call mine 1/3 stop and you call yours 30%

Exactly! The only thing I don't have with percentages that you have with f-stop timing is the headache!

As Bob points out, the percentages and the stops are not exactly equivalent (and reciprocity failure is always a factor at longer times), however percentages are consistent and flexible and have all the advantages and none of the drawbacks of f-stop timing. I have two sequences, 20% and 30%, that I use for test strips and have simply memorized them. No programming, no math, nothing but counting seconds.

Seriously, it seems to me that so many f-stop timing schemes (and timers!) are overly-complicated for the task at hand. Percentages are easily figured and rounded, and I can just use my metronome to time with and watch my work. Plus I have the advantage that I can apply the same system to dodging and burning, which is rather difficult with f-stop timing (how do you dodge 1/3 stop anyway?).

And, when scaling a print up or down, I can find a base exposure and then use the percentages I've recorded to figure a starting point for manipulations for the new size. I say starting point because different size prints often require very different approaches to get the same "feel."

Best,

Doremus

 

[Bob Carnie]

When I worked in the 80s doing huge murals we worked with a mag formulation that considered reciprocity , and therefore once we established a set time at one magnification
then we could calculate fstop differences without adjusting the timer unless in extreme changes.

Quite frankly I cannot tell you all how this was done today as my mind is old and feeble.

I am a strong proponent of keeping my times within 10 -18 seconds so that the math will work out in % 's, but since we all have different types of enlargers. and different types of negatives our times may vary.
I do use three bulbs on my enlargers .. 75w, 150 w and a 250 ww depending on the negative therefore keeping my times to the sweet spot as well keeping in the middle areas of my apeture without going to the extremes.
I have heard of some here doing 2 minute exposures which if find impractical.

I also utilize ND to lower the power of my 11 x14 and 8 x10 enlargers so that I am almost always in the sweet spot.

I just finished 4 different negatives for mural silver prints and was able to print at two stops down and between 12 and 16 seconds.
This way I can use predictable % printing as some here suggest to do.
Also I use glass carriers and will adjust the apeture once focused to change density if my time is in the sweet spot.