Confusion with quote from Blakemore

Toffle · May 28, 2016

Reading through my copy of John Blakemore's Black and White Photography Workshop the other day, I came across the following advice:

"...If, for example, your chosen time is 20 seconds, and your test strip was made at 4-second intervals, then give 5 x the 4-second exposure. One single exposure of 20 seconds would yield a darker print." P.87

I feel like I'm missing something here. Is he powering his lamp up for each increment of the test strip, and then accounting for the warm-up/cool-down time of the lamp? Is there some characteristic of the paper that I am misunderstanding? Does everybody else know this except me?

Cheers,
Tom

MartinP · May 28, 2016

It seems that he is assuming that four 'extra' sets of warm-up time for the lamp are not outweighed by having four 'extra' cool-down times - when considering (1x20s) vs (5x4s) of exposure. A better way of doing the test-strips might be to have a metronome ticking away and then move quickly a piece of card over the paper at the appropriate number of beeps. Even better would be to make a test-strip printer (ie.moving the paper to give multiple tests using the same part of the image) and set the appropriate time for each strip using the timer rather than some sort of multi-exposure.

Ian Grant · May 28, 2016

He's saying that if your test strip exposure of 20 seconds is 5 x 4 seconds (and that's your chosen exposure) then your first print should be made up of 5 4 second exposures because a 20 second continuous exposure will be darker, for the reasons above. I've been on two Blakemore workshops and he's a brilliant printer. He's basically saying be aware that 4x5 and 20 aren't quite exact in exposure terms

I usually cut a sheet of paper into 4 or 5 to do the test strips, in practice I use one of these pieces of paper and expose it for the full chosen exposure which is typically in between two of the steps on the test strip anyway, I might make a further slight adjustment before a first full print.

Ian

pdeeh · May 28, 2016

I ran into exactly this problem when I was first printing, and it really can happen that if you mix continuous with on/off exposure, you end up with significantly different results on the print.
I now always leave the lamp on and move a mask to make test strips.

Barry Thornton also mentions the problem in his "unZone" article, here: Dead Link Removed

Vaughn · May 28, 2016

I don't worry about it. I slightly adjust the exposure time as I print an image, anyway. The test strip is just to get me within 10% of the 'best' time. And besides the 'best time' never seems to be one of the times used, but instead I have to split the difference..."Looks closer to 20 seconds than 15 -- I'll try 18."

Ian Grant · May 28, 2016

Having seen John Blakemore printing he doesn't worry about it either. His comments in the book are really to say beware this happens.

Ian

Doremus Scudder · May 28, 2016

Blakemore (and the late Fred Picker as well) apparently uses separate, shorter exposures to make a test strip. Due to a number of things, such as the intermittency effect, warm-up and cool-down of light sources, timer inaccuracies, etc., a continuous 20 second exposure is not the same as five 4-second bursts. It will be a bit less exposure.

If, like me, you make your test strips with a continuous exposure, then you don't have to worry about this, or make your final print with a series of bursts of light.

I use a metronome and count seconds. I make the test strip by successively covering parts of the test strip at regular intervals. No need to switch the enlarger lamp on and off a hundred times in a printing session...

And, as Vaughn points out, exposure adjustments are usually made after the first full print is made anyway. It would make sense, however, to use the same method for test strips as for the final print

Doremus

Toffle · May 28, 2016

Is there an advantage to using separate bursts for test strips?

I was taught using continuous light and a moving mask, presumably to take the warm-up/cool-down times out of the equation. That way, 20 seconds on the test strip is the same exposure during enlargement. Besides, I don't think I could be all that accurate fumbling with the switches on my timer; it's one of those Gralabs on which the buttons are moisture-protected with soft plastic caps.

Like Vaughn, I often split the difference between exposures, but for my own piece of mind, I use Ralph's F-Stop printing chart to calculate my times.

Thanks for the link to the Barry Thornton article. I hadn't read him in quite awhile.

So, how about you guys... who uses continuous light for test strips, and who does separate bursts?

Cheers,
Tom

Vaughn · May 28, 2016

I use bursts for the test, continuous for the print. I have just not found the difference to be significant. If the time it takes for the bulb to reach full brightness is close to the time it takes to dim, then the amount of light is going to be damn close to using continous -- close enough to be insignificant unless one likes to worry about such things.

I suppose we could worry about that a small test strip is not going to be developed exactly like a full sheet of paper (how fast the paper gets in the developer, agitation differences , etc) -- and try to compensate for that! LOL!

Ian Grant · May 28, 2016

Toffle said:
Is there an advantage to using separate bursts for test strips?

It's six of one and half a dozen of the other.

The advantage is accurate steps compared to timing with a clock and moving visually every so many seconds but you get this slight underexposure compared to a continuous exposure.

As it's only getting you within the ball park of two steps so it's whatever you feel happier with. I use multiple exposures and then err slightly towards very slightly less than the strip might indicate.

Ian

Vaughn · May 28, 2016

Ian Grant said:
It's six of one and half a dozen of the other...Ian

Or three pairs of something else!

Toffle · May 28, 2016

I am encouraged that the gist of this thread is "don't worry about it". I certainly don't. The purpose of my question was to clarify that he was, in fact, using bursts, as I don't think he explicitly said so in the book. (I may be mistaken, but I didn't see it stated.) If he wasn't, I would be very confused indeed.

John is one of the printers I would love to see in action. I would love to give him my best negative (or my worst) and see what he could do with it. For that matter, I would find it so inspiring to share an hour in the darkroom with any accomplished printer. I have attended many photographers' gatherings, photo shoots and print showings, but have yet to stand shoulder to shoulder with a master printer to see how they work their magic.

MattKing · May 28, 2016

I have a timer that needs service - some times it won't power up both the yellow filtered lamp and the magenta filtered lamp after I switch times. So I prefer to reduce the number of times I change times - I frequently work with multiples of a single time rather than one longer time.

As others have pointed out, you will get more exposure with one long exposure than with several shorter exposures. Each warm-up and shut-down cycle reduces the exposure compared to being on continuously. The purpose of the quoted passage is to warn the reader about the existence of the difference.

DWThomas · May 28, 2016

Lessee an Arduino, a stepper motor and a small rack and pinion to move the test strip .......

Steve Goldstein · May 30, 2016

Yes, there's a difference between using multiple short exposures and a single long exposure arising from the warmup and cooldown time of the bulb, and the effect is most important with short exposures. You can test it for your enlarger using the procedure here:

http://www.darkroomautomation.com/support/AppNotePH212LampDelay.pdf

For my Zone-VI stabilized 4x5 Aristo cold light head (V54 bulb) I found that the actual exposure at the intensity setting I always use is 0.1sec less than my timer indicates. So if I want 9.0sec of light I can use either a single 9.1sec exposure or three 3.1sec exposures to get identical results.

RalphLambrecht · May 31, 2016

Toffle said:
Reading through my copy of John Blakemore's Black and White Photography Workshop the other day, I came across the following advice:

"...If, for example, your chosen time is 20 seconds, and your test strip was made at 4-second intervals, then give 5 x the 4-second exposure. One single exposure of 20 seconds would yield a darker print." P.87

I feel like I'm missing something here. Is he powering his lamp up for each increment of the test strip, and then accounting for the warm-up/cool-down time of the lamp? Is there some characteristic of the paper that I am misunderstanding? Does everybody else know this except me?

Cheers,
Tom

He is talking nonsense and makes test strips just as bad as Picker with his 3s intervals; The best test strips are made with f/stop timing;Don't pick up this bad habit of piecing exposures together.

baachitraka · May 31, 2016

F-stop printing is nice, provided if you have nice setup like what Ralph has taught in his book.

RauschenOderKorn · May 31, 2016

baachitraka said:
F-stop printing is nice, provided if you have nice setup like what Ralph has taught in his book.

Actually you can make a test strip with f/stop timing with almost any equipment, even a normal darkroom timer.
The fancy equipment makes it easier, but f/stop timing goes way back before the electronics was available.

Ian Grant · May 31, 2016

RalphLambrecht said:
He is talking nonsense and makes test strips just as bad as Picker with his 3s intervals; The best test strips are made with f/stop timing;Don't pick up this bad habit of piecing exposures together.

John Blakemore is probably one of the worlds best printers, he makes Ansel Adams look like a mere beginner. He's talking total sense and just warning that multiple exposures don't add up to the expected total. See Steve Goldsteins post above.

This isn't unique to printing it's similar when making multiple exposures on film although not quite for the same reasons.

Ian

baachitraka · May 31, 2016

RauschenOderKorn said:
Actually you can make a test strip with f/stop timing with almost any equipment, even a normal darkroom timer.
The fancy equipment makes it easier, but f/stop timing goes way back before the electronics was available.

Indeed. A nice f-stop timer/printer is always handy. Sometimes, I am too tired of changing the times for each and every strip.

Nevertheless, most of the time the exposure fell with in 10sec(10.1s).

Toffle · May 31, 2016

RalphLambrecht said:
He is talking nonsense and makes test strips just as bad as Picker with his 3s intervals; The best test strips are made with f/stop timing;Don't pick up this bad habit of piecing exposures together.

Just a couple of paragraphs above the offending quote, Blakemore also recommends doing one-stop exposures, "if you are unsure of your likely exposure". For my own printing, I use f-stop tests, though I'm not above eyeballing a negative to narrow the range of times of my tests.

Doremus Scudder · Jun 1, 2016

As an aside to the thread, but hopefully useful to those without f-stop timers, etc.

Yes, it is best to expose test strips proportionally, i.e., with each strip getting a proportionally longer exposure time. F-stop timing is one way to do this and intuitive for many. I find it cumbersome.

For me, it is far simpler to use percentages. I make my first test strip (and usually my last) in approximate 20% increments. I've simply memorized the sequence "2, 2, 3, 3, 4, 5, 6."

How does this work? I step on the footswitch to the audible timer (set to beep once a second and set to maximum time of 99 seconds) and count a base exposure of 10 seconds. At 10 seconds I cover part of the test strip and count 2 seconds, at which point I cover another strip, count another 2 seconds and cover another strip. At 3 more seconds I cover another strip and so on through the sequence.

This gives me a test strip in approximate 20% increments (10-12-14-17-20-24-29-35 seconds) from 10-35 seconds. It's pretty easy to extrapolate the 10% intermediate times when needed. That's way close enough to begin with a full-size print. FWIW, I express my dodging and burning schemes in percentages of the base exposure as well. Easy to figure in my head and helpful when reprinting at a different size, since my base exposure will vary, but the percentages will remain the same and provide a good starting point.

Some find 20% increments too small, but I like them. However, 30% is easy too, just memorize "3, 4, 5, 7, 9," which, when starting with a 10-second base exposure, results in a test strip with 10-13-17-22-29-38 seconds.

Using same-time increments to make a test strip is just worthless, IM-HO. The difference between 10 and 13 seconds is 30%; the difference between 30 and 33 seconds is only 3%... And I agree wholeheartedly with Ralph about not piecing exposures together.

Best,

Doremus

gone · Jun 1, 2016

Which is why one should make small test prints using the same paper that will be used to enlarge the final big print. That way you know 100% what you'll get. A regular darkroom timer is fine for test strips, or a metronome, count down yourself, etc. The simpler you make things, the more consistent the results and the better the final image quality.

Confusion with quote from Blakemore

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