Test strip times and printing times

[Ray Heath]

The result on the paper (or film, come to that) depends on the volume of light delivered to it, and this is the product of the lens aperture and the exposure time. Adjusting either affects the result. So it makes perfect sense to use a logarithmic sequence of exposure times as well as lens apertures. Yes, they are different measures, but the effect on the exposure is exactly the same.

Look on your camera: do you not see a similar logarithmic sequence of shutter speeds? Nobody questions that. So why is nonsensical to use a similar sequence when making a print?

As for bulb warm-up and cool-down, these largely cancel each other out and the effects on any but the shortest exposures are minimal in my experience.

of course, for macro adjustment, but for fine adjustment full seconds are no less 'correct' than parts of seconds just because they are partial stops

 

[Ray Heath]

It occurs to me that if you use a sequence of exposure strips on a sheet of paper and then decide on a base exposure from those choices, you can make another test strip with your timer set to that amount of time. You can observe the difference with your binocular, wetware metering system and make a decision about a minor adjustment (if needed) based on empirical observation. You could even develop a chart for these compensations..ie how much to add or subtract for any number of eliminated start/stop cycles when extrapolating an exposure from test strips.

why keep complicating the issue?

e.g. if your first test strip of 5 +5 +5 +5 +5 indicates somewhere around 20 secs, do another test at 15secs +3 +3, that may then indicate the 'correct' exposure to be something like 19 secs

f stopping, using meters or any other device or technique won't be anymore accurate

 

[Joe VanCleave]

Exposure Slit Method

Kodak used to recommend a single 60 second exposure with a cardboard covering the print for varying times. Thus the portion of the strip exposed for the full 60 seconds would be darkest and each of the sections would recieve 10 seconds less exposure...
PE

When I was recently performing calibration tests of preflashing paper negatives, for use in pinhole and alternative lens cameras, I came to the realization that the method you refer to here, which I have used for years in making test exposures for prints, is basically flawed.

Let's say I set the timer for 60 seconds, and uncover each additional section of the strip at the '10 second' mark; i.e. the strip gets successively uncovered at the :50, :40, :30, :20, and :10 marks. Then, let's say I find that the strip corresponding to 20 seconds is my preferred exposure time, so I set the enlarger timer for 20 seconds. Well, when the test strip was made, the enlarger bulb had been on and warming for 40 seconds prior to this section of the test strip being exposed, but when I make my print, the bulb starts the 20 second exposure cold. This essentially reaffirms what others have indicated regarding lamp warmup time.

I found this to be a significant source of error when attempting to find the shortest time that shows a measurable density change on my grade 2 RC paper negatives (i.e. my preferred preflash time).

So what I now do is use an opaque card with a long, narrow slit cut lengthwise, whose width is equal to each test strip section. Now, I set the time for 10 seconds, and expose the 10 second section; then I set it for 20 and expose the 20 second section, etc. The remaining areas of the test strip are not exposed, except during their respective times when the slit overlaps these areas, and the once-exposed areas are not additionally exposed when the remaining sections are.

I don't believe this method is what others are referring to as the 'f/stop' enlarging method, since my time increments are linear rather than logarithmic, but it seems to be accurate for me, and eliminates errors introduced by lamp warmup time. It also seems likely that the issue of lamp warmup time is completely seperate from that of logarithmic exposure times; i.e. it's possible to mess up an 'f/stop' exposure system and not take into account lamp warmup time, as my exposure slit method does.

 

[jstraw]

why keep complicating the issue?

e.g. if your first test strip of 5 +5 +5 +5 +5 indicates somewhere around 20 secs, do another test at 15secs +3 +3, that may then indicate the 'correct' exposure to be something like 19 secs

f stopping, using meters or any other device or technique won't be anymore accurate

The issue for me isn't accuracy, the issue is usefulness. Either you see how even distribution of print exposure values would be more useful than a series of ever-decreasing differences would be or you don't. It's useful to me. It's ok with me if it's not useful to you.

 

[RalphLambrecht]

why keep complicating the issue?

e.g. if your first test strip of 5 +5 +5 +5 +5 indicates somewhere around 20 secs, do another test at 15secs +3 +3, that may then indicate the 'correct' exposure to be something like 19 secs

f stopping, using meters or any other device or technique won't be anymore accurate

f/stop timing will potentially get you there quicker. A linerar timing sequence creates uneven differences. First the differences is large (10+5 = +50%) then it get smaller (20+5 = +25%). f/stop timing provides even exposure increases, making test strips more meaningful.

 

[RalphLambrecht]

who, if you stop kidding yourself, can see the difference in density between 20.9 and 30 seconds

Nobody, because it's only about 1/24 stop. Nevertheless, you can see 1/12 stop easily on normal grade paper. The beauty is that the f/stop differences are always the same, regardless of exposure time. Linear timing diferences vary with exposure time.

Look at the attached file. Major increments are in 1/3 stops, minor increments in 1/6 and 1/12 stops.

 

[RalphLambrecht]

who'd notice, 1.7 secs in 20 is not gonna make any appreciable density difference

Depends on what you call appreciable. 1.7s in 20s is over 1/12 stop and can easily be seen on normal grade paper and even more so on harder paper. But I think you are getting hung up on the fraction of a second issue. f/stop timing is about even exposure spacing in test strips and flexible print exposure records. You can use any timer for f/stop timing, just use an f/stop timing table and round the recommendations to the closest full second. The error will be minute (never more rthan 1/12 stop with my tables), but the benfit will still be great.

 

[RalphLambrecht]

Far too coarse and never in the right place.

 

[RalphLambrecht]

1/4 stop steps are too big for you?

The rule-of-thumb in f/stop timing is that 1/3, 1/6 and 1/12 stop are coarse, medium and fine, respectively. These steps are roughly equivalent to 5, 10 and 20%. I use a seven-step test printer, which gives me a full stop difference between the first and last step when using 1/3 stops. This is usually enough to pick a 'close' step and do it again around that step in 1/12 stop increments.

 

[RalphLambrecht]

f/stop timers are a big help, but don't forget, you can do it with just a table and any good linear timer. Having said that, I love my f/stop timer.

 

[RalphLambrecht]

of course, for macro adjustment, but for fine adjustment full seconds are no less 'correct' than parts of seconds just because they are partial stops

Correct, but which full second is the best. To me, it is the one after rounding the f/stop recommendation.

 

[jstraw]

Todd

Make the print exposure for the same time and in the same way as you did the best test exposure. For your interest, my free article on f/stop timing, which includes a table, is still available on my website at:

Dead Link Removed

Ralph, are you aware that the pdf file is locked down so that the article may not be printed?

 

[RalphLambrecht]

Ralph, are you aware that the pdf file is locked down so that the article may not be printed?

No, I wasn't. That makes no sense, and I'll fix that. Thanks for telling me.

 

[jstraw]

No, I wasn't. That makes no sense, and I'll fix that. Thanks for telling me.

That would be great. Thanks very much.

 

[RalphLambrecht]

That would be great. Thanks very much.

I'm happy to announce that all PDFs on my website are now printable! However, you may have to reset your browser, if the date you see on my home page is a date prior to 2006-Oct-24. If the date is 2006-Oct-24 or later, you're fine. Happy downloading, and don't hesitate to tell mail me if you have any other suggestions.