PDA

View Full Version : Using a step tablet. Please clarify



coops
19-May-2010, 09:40
So I am of course a newby to b&w printing, and having mixed results with my printing. I have a 4x5 stouffer 21 step wedge, and a color head on my enlarger, but not sure what do do with it. My understanding is that I want to find an exposure time that produces black at one end and white at the other, and about 17 discernable steps in the middle. The first two blacks and the last two whites may look the same.
Lets say at F/16 it takes 10 seconds. I guess I know that for the paper/developer combination I can do test prints at around 10 secs? Some of my negatives require more. So I am confused about what this tells me.
Also, the limited success I have had was done using the yellow and magenta filters in the head, and doing split grade printing. Do I need to test each filter and combination of filters with the tablet in increments of say 50? I am still left with the same question of exactly what info I am left with and what I do with it.

I apologize if this is really a dumb question. I have a feeling it may be a case of not seeing the trees for the forrest. I have done some reading but the books I have seem to assume the reader knos a lot more than I already do. Any help much appreciated.

Cheers

W K Longcor
19-May-2010, 10:04
I've been retired from the photog business for a while now and haven't done any printing -- so I get worried when I offer advice -- I may not be up to date. Anyway, I think you are making it all to complicated. Put the step tablet in a nice safe envelope and put it on the shelf. :D Take one of YOUR NEGATIVES and make test exposures. You are looking for the LEAST exposure that produces a MAXIMUM BLACK from a clear area ( base plus fog, as they say) -- maybe an unexposed boarder area. If your mid or light tones are too light or too dark -- then you have to adjust contrast (paper grade or multi-contrast filter ---in your case , the filters in your color head. ) While things like artistic license may come into play -- you want a lighter or darker print, maybe----- the "correct" exposure (technically) wll be that minimum that gives maximum black in the base plus fog area of the film. The step tablet will never really match YOUR negatives - so in the case of printing like this -- it does not really help. Hope this will get you started. Most important, while in the darkroom -- have fun!:)

P.S. -- Of great importance when printing. STANDARDIZE your developer, dilution and development time and agitation. When you are figuring out exposure and contrast -- always use the same developer --ALWAYS develop to a standardized time (2 minutes or whatever is considered proper for the developer / paper combination) -- ALWAYS the same---you can start varying times , etc, when you become expert in the printing techniques.

jp
19-May-2010, 11:24
My understanding is that you could print something with the wedge over it with some overexposure, and the wedge would tell you how much should reduce exposure to get the right print exposure based on which portion of the wedge looked right. It would simply be a more accurate and simple replacement for traditional test strips (where you uncover additional portions paper at intervals.)

You could make something similar on a bigger scale with a sheet of mylar and a laser printer, but dot gain would likely prevent accurate steps of gray output.

CG
19-May-2010, 12:09
A couple of the many uses for step wedges...

1. For a record of the effects of a given toner. Make two identical contact prints onto a kind of paper you want to tone. Just print the step wedge alone - no negative - just the step wedge. Expose so that the contact prints show a full range of tones from black to white. Tone one and leave the other untouched. You will be able to see what change in color, density and contrast occur from that toner. Keeping those will give you a very good record of the performance of that toner on that paper. And it shows the performance at each density. You will see what density you lose or gain. What color shifts occur at each step...

2. To determine normal - and plus and minus - development for film. Contact print the step wedge onto pieces of film. Test to find an exposure that is just enough so that the darkest part of the step wedge gives you clear film, and the next gives you a slight density. All the rest of the steps will give exactly graded steps of increasing density one exposure zone apart. Develop those pieces for differing times and then print them on whatever paper grade that you use as normal. You will have a pretty fair picture of what developing times will allow what range of subject brightnesses or zones to print without manipulation. Not a bad way to rough out a set of development times.

Joe Smigiel
19-May-2010, 22:44
...I have a 4x5 stouffer 21 step wedge, and a color head on my enlarger, but not sure what do do with it. My understanding is that I want to find an exposure time that produces black at one end and white at the other, and about 17 discernable steps in the middle. The first two blacks and the last two whites may look the same.

I'm doing this from memory and haven't printed with a stepwedge in a few years, but hopefully I won't misspeak here.

Each step of the 21-step wedge represents a 1/2-stop change in exposure. Each step is approximately .15 density more than the preceding one. (Note that a 31-step wedge in contrast has 1/3 stop changes per step with a density of approximately 0.10 per step.) 17 steps on a 21-step wedge would represent a density of ~2.45 which is way way way way way too much for normal silverprinting. (The first step is around .05 & the rest increase about .15 density units per step.) IIRC, my tests of Ilford Multigrade Warmtone FB with a #2 contrast grade got about 1.45 from max black to white when printing a stepwedge. That's about 9.5 steps.

You should be able to find on the web some sort of lookup table for your colorhead that has suggested settings for yellow and magenta filtration for various contrast grades. Set a normal contrast grade (e.g., #2) on the colorhead. Take a sheet of paper of the type you will normally print upon and make a contact print of the stepwedge at a setting you believe will grossly overexpose the low end (thin areas) of the stepwedge. Let's assume an example of 60 seconds at f/5.6 is what you give. Process the sheet normally and examine it.

Hopefully the low steps will be all blocked up. Let's say the first discernible dark gray step lighter than max black is step #6. You want to shift the scale so that point occurs at step #2. (The density of step #1 is about 0.05 and the rest of the steps increase at about 0.15 density units per step. So, Step #1 is a bit thinner than your sheet film base and you want to give slightly more exposure than what it takes to print that step as maximum black. Hence, shift the black tone to step #2.)

There is a table on the reverse of the stepwedge envelope that tells you the multiplication factor to apply to your test exposure to shift the scale up or down. In this example, you want to go from step #6 to step#2 or a 4-step (not stop) shift. 4 steps is 2 stops. So, you want to reduce exposure from 60 sec @ f/5.6 to 15 sec @ f/5.6 (or some equivalent that is two stops less than the original exposure). That should make only steps #1 & #2 maximum black. The factor on the envelope for this shift should equal 0.25x. [60 sec x .25 = 15 sec which is a 2-stop (or 4-step) decrease or 1/4 the original exposure.] That's your exposure time for a proper proof with this film/paper/filter combo assuming the film-base + fog level of the film is close to the stepwedge step #1 density.

Then check to see where the highlights go paper white and block up beyond that step. That will tell you how many steps your printing paper can handle with the filter chosen. (The "exposure scale" of the paper is defined slightly differently taking 90% black and threshold light gray steps as the chosen points IIRC and depending on who you read.) The number of steps from black to white will vary depending on the filter chosen. You'll want to ultimately adjust your process (particularly film exposure and development) to match the density range of the negative to the exposure scale of the paper at a certain filter setting in order to get a good print. IOW, at the paper's proper proof exposure time determined with the stepwedge test, you'll want a subject value in your negative you envision to tonally reproduce as threshold gray (Zone VIII in most books) to actually match the density of the step that printed as the light gray threshold tone on the stepwedge proof.


Lets say at F/16 it takes 10 seconds. I guess I know that for the paper/developer combination I can do test prints at around 10 secs? Some of my negatives require more. So I am confused about what this tells me.

Now I'm confused by what you are saying about the 10 second @ f/16 exposure being correct. Why do you think so? Is it because the print looks good or the stepwedge printed 17 steps or the black occurs at step #2 or ???

The variation is telling you your technique is inconsistent for some reason (metering, exposure, visualization error, over- or underdevelopment of the paper or film, wrong filter setting, etc.)


Also, the limited success I have had was done using the yellow and magenta filters in the head, and doing split grade printing. Do I need to test each filter and combination of filters with the tablet in increments of say 50? I am still left with the same question of exactly what info I am left with and what I do with it.

I wouldn't start worrying about split-filter printing until you have a basic one-filter method working for you. I'm also not sure the testing for split-filter printing would work with a stepwedge. The low contrast layer isn't ever going to give you a good black in a reasonable exposure time.

What you might want to do is make a good print after testing with one normal filter setting. Then use the number 00 and 5 filters to make a checkerboard exposure test (i.e., the low contrast layer strips go vertically and the high contrast strips are then run horizontally-one of the resultant squares should match your good print). That would at least get you in the ballpark for split-filter times for normal negatives. (I think.)



I apologize if this is really a dumb question. I have a feeling it may be a case of not seeing the trees for the forrest. I have done some reading but the books I have seem to assume the reader knos a lot more than I already do. Any help much appreciated.

Cheers

Not a dumb question at all. It takes some time and experience to wrap your head around this density stuff. Hope I've cleared some of it up for you rather than making it more confusing. Once you know the exposure scale of the paper, you can then work on figuring out how to get the negative density range to match. Most books never tell you to start with the paper scale testing first. But, if you think about it, you want to know how big of a box you need (i.e., the paper range) before you can tell how much stuff (i.e., negative density) can be put in the box.

Hope this helps.

Joe

coops
20-May-2010, 15:15
Thanks for all the info. Joe, you spent some time typing all that, it makes sense and I appreciate it.

Joe Smigiel
21-May-2010, 00:08
You are welcome. But, I have to make a couple corrections to the above but can't edit the original post.

First, I omitted the fact the contact test should be done at the enlarger height where you would normally print your negative. That will eliminate problems with light intensity.

Second, I said: Let's say the first discernible dark gray step lighter than max black is step #6. You want to shift the scale so that point occurs at step #2.

That should read: "Let's say the first discernible dark gray step lighter than max black is step #7. You want to shift the scale so that point occurs at step #3."

That will make the max black tone appear on step #2 which is what I intended to convey. Max black should end up at step #2 and white should probably be around step #10 (transmission density of ~1.40) depending on the paper and filter.

ic-racer
21-May-2010, 05:40
The step wedge is to determine the range of values or ISO(R) or GRADE of you paper. Assuming you need this info (which you don't really).

To get the ISO(R) count the number of gray bars. Throw out the one that is "just white" and "just black" and count the rest. Multiply by 15 and that is your ISO(R).

You can also use the stepwedge to help calibrate you color head to keep printing times constant as you change contrast, but I'd try one of the published Ilford tables first and see how that works first. It can be a lot of work to get a good table. Here is a thread showing how I do it: http://www.apug.org/forums/forum41/55179-making-multigrade-calibration-table-color-head.html

Recommendation:
1) Forget about the step wedge
2) Get some Ilford Multigrade paper
3) Use the chart that comes with the paper for your contrast control settings
4) Make prints!