Densitometer + Dektol 1:9 + ERA 100 + Step Tablet

Anon Ymous said:

Go ahead. Even if I don't understand something, chances are that someone else will have an answer.

Click to expand...

One of my first "?" is -

how do I convert my light meter readings into Lux? or better, into milliLux as used referred to in the article.

The next thing to figure out is how to translate the step tablet density readings (straight from the Stouffer wedge) into exposures? (this is so that I can have a graph that does not have "steps" on it, but actual log Exposure units...

In order to perform some of the analyses the manual talks about I'd need to be able to count log exposure units. Right now, all I have (I believe) are density measurements of the Stouffer Tablet and of my test negs, plus the meter readings from when I made the exposures.

Lastly, when I made the measurements for the exposure I used my light meter as an incident meter. I set it to f/1, and fiddled with the aperture and height of the enlarger lens till it gave me a one second exposure.
I'm still not totally certain HOW that aperture setting was "right" ... if indeed it was right... but it was intuitive. I guess part of my mind thought - if the aperture is "1" then the lens is delivering all the light that falls on the lens to the film plane (this is probably poor reasoning, maybe the right action, but for the wrong reasons).
Because I was making a contact print, the only aperture to monkey with was at "the light source". . .. and not at the "film plane" at all.

Er.. back to Kodak's article on sensitometry:

I'd like to be able to read my curve and know, according to Kodak, that the film was "properly" developed. To do that I have to count an actual LogE change of 1.30 With my current system I can't do that b/c I don't know what the exposure is, in milliLux, that gets to the film behind each step of the Stouffer tablet.

Once I fiddled with development till it was technically correct, THEN it would be time to sort out "speed point".

In order to convert light meter readings to lux, you'll need to know the EV that the meter reads. EV0 is 2,5lux. For every 1 unit increase of EV, you'll need to double the lux value, thus EV1 is 5lux, EV2 is 10lux etc. EV-1 is 1,25lux. EV is exposure value. If speed is set at 100ISO, then EV0 is 1 second exposure with an f/1 aperture. Of course, that would be equal to 2 seconds with f/1,4 and so on. Now, if you want to convert lux to millilux, just multiply by 1000. Milli is a thousandth, like millimeter is 1/1000 of a meter.

Regarding the readings you get from your densitometer, are you sure they're not logarithmic?

(edit - I see you posted while I was off looking these up Thanks!)


Um...

not liking to simply whine

I found that an exposure of 1s at f/1 gives me a EV of 0 (zero). This info here.
I then found an EV to Lux (and vice versa) conversion calculator. Here.


OK.. so now I know that the amount of light falling on the step tablet was 2.5 Lux or 25,000 millilux.
Taking the log of 25,000 (here) gives me 4.4 (rounding up one tenth of one percent)

Everything so far is peachy, but then on page seven of the Kodak manual on sensitometry there may be a first "hiccup"...

In the section describing "figuring exposure" on page seven, the model used has a filter that takes out some of the exposure. In my process there was no such filter (well, the glass of the contact frame, which I have not properly measured... but which, until I have reason to suspect I need to measure, I'll consider to have no effect on exposure).

Now that I have exposure units I can work with, I'll have to go measure the steps on my Stouffer tablet to know how much each step reduces exposure.
I'd then subtract that much exposure from the total incident light, and THAT would tell me where on the logE scale I should plot each one of my density measurements.

Geez Louise... this might all end up as actual curves after all.

Anon Ymous said:

In order to convert light meter readings to lux, you'll need to know the EV that the meter reads. EV0 is 2,5lux. For every 1 unit increase of EV, you'll need to double the lux value, thus EV1 is 5lux, EV2 is 10lux etc. EV-1 is 1,25lux. EV is exposure value. If speed is set at 100ISO, then EV0 is 1 second exposure with an f/1 aperture. Of course, that would be equal to 2 seconds with f/1,4 and so on. Now, if you want to convert lux to millilux, just multiply by 1000. Milli is a thousandth, like millimeter is 1/1000 of a meter.

Regarding the readings you get from your densitometer, are you sure they're not logarithmic?

Click to expand...

I'm with you everywhere but one place:

How would the EV change if the ISO the meter was set to was "50"....
It's twice the amount of light... so would it simply double the EV? and that would mean an EV of -1 ?

And as to the readings of the densitometer... I'm fairly confident the readings are logs. I'm not certain, but fairly confident. Or, in other words - I'm fairly happy to assume that they are for the sake of seeing how the numbers fit the calculations the Kodak article asks of the reader to perform. So far, so good. Whatever language the Kodak article was written in (mathematically), my densitometer seems to speak it.

After looking around some more it seems that (this is an invite for anyone to correct me) EV 0 is 1s at f/1 for any film speed.
So EV 0 is still 2.5 Lux, which is still 25,000 millilux. The log of which is 4.4

OK... that's clear. Next step, get density values for the step wedge, and subtract them from the Log E numbers.

ahhh....
crap.
I'm wrong.

Here is an EV calculator, indeed, as the ISO goes down the EV of 1s at f/1 is equal to "EV 1"

Which means that my exposure was 50,000 millilux.

Which gives me a total log exposure of 4.7

Pastiche said:

... So EV 0 is still 2.5 Lux, which is still 25,000 millilux. The log of which is 4.4 ...

Click to expand...

That's one zero too many. 2.5 lux is equal to 2,500 millilux. log(2500) = 3.4

By the way, you'll need to develop some unexposed film with exactly the same procedure (developer + dilution, time, agitation, temperature). The reading from that piece will give you film base + fog density. Unless of course you kept some part of your film covered during exposure, in which case you'll take a reading from that part.

Anon Ymous said:

By the way, you'll need to develop some unexposed film with exactly the same procedure (developer + dilution, time, agitation, temperature). The reading from that piece will give you film base + fog density. Unless of course you kept some part of your film covered during exposure, in which case you'll take a reading from that part.

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You can do this by putting a piece of opaque tape onto your Stouffer step wedge. I used some silver mylar tape, but one could use some black electrical tape. I put mine in the middle between steps 1 and 21 on my 21 step wedge. I read the density of that spot and use if for the B+F value. It is often different than the most dense step, so you do need to do something like a blank sheet or a section of the step wedge that's covered with some more opaque material.

Densitometer Units - you're most certainly using "log" units when you are measuring optical density.

For your exposure calculations - you want to be using lux-seconds. You've measured the amount of illuminance that you're making the exposure with, so now you need to mulitply the illuminance in lux with the exposure time in seconds. So if you have 2.5 Lux and you used a 0.5 second exposure time, then your total exposure is 1.25 Lux-seconds. Take the log of this, and you get 0.097. That's your base exposure, and all the other exposures through the step wedge will have an exposure value that is less than this value.

Also, I'd stick with lux and not millilux, as it makes the math with your step wegdge densities easier to calculate. Even though the Kodak page has some calcs with millilux, it's easier to just stick with lux-seconds. And you get a bonus that your graphs will have the same units used on Kodak Technical data sheets for their films.

Now you take your step wedge densities, which are already in log units of optical density, and you can subtract the density of each step from the base exposure in lux-seconds that you determined above. If the first step on your Stouffer has an optical density (OD) of 0.15, then the exposure for that step is 0.097-0.15= -0.053 lux-seconds. The next step, if it is 0.30 OD, is equal to 0.097-0.30 = -0.203 lux-seconds. And so on for the rest of the steps. For the portion where I put the tape, I just figure it's 1.0 or whatever above the most dense step, so I just figure that "step" has a opitcal density of 4 or 5 OD, then I subtract 4 or 5 from my base lux-second exposure value to plot that point.

Plot the densities from your test film vs. the exposures in lux-seconds for each of the steps and you have a H&D curve in the actual units needed to make your film speed calculations.

I might have missed it, but did you use a spot meter or incident meter to determine your lux value?

If you used a spot meter, did you meter off a grey card? It's actually probably more accurate to use an incident meter with a flat diffuser over the sensor to measure illuminance.

This thread, (minus this post) should be printed and published. It's the only narrative I've seen on BTZS where the confusions arise and are answered and discussed as they arise.

Bob H

Thanks Kirk.

We are pretty much on the same page! (which is a delight for me, as I haven't know what page I've been on until late last night.

When I start figuring exposure I'll run it both in millilux and then Lux, just to see what seems most convenient.

Oh... I just measured my blank sheet of film, fb+f = .18
This value is what I was assuming for the curves generated in my last graph. (lucky guess )

On my measurement process, I used an incident reading, at the "film plane" (height of the contact frame). The measurement was ISO 50, 1s, f/1.

Next step, measure the density of the steps on my Stouffer wedge.

BobNewYork said:

This thread,... the only narrative I've seen on BTZS where the confusions arise and are answered and discussed as they arise.

Bob H

Click to expand...

Ha! hahahaha....

Well, it is humbling to stumble through the process "out in open air", but it's kosher as I don't have any kind of "reputation" to protect

Plus, if I didn't blunder along and ask lots of questions I might end up either giving up or getting bunk answers

Pastiche said:

Ha! hahahaha....

Well, it is humbling to stumble through the process "out in open air", but it's kosher as I don't have any kind of "reputation" to protect

Plus, if I didn't blunder along and ask lots of questions I might end up either giving up or getting bunk answers

Click to expand...

We all stumbled my friend - anyone who tells you they didn't is.....!!! It's very cool to see your progress and grasp of the underlying facts. You may, in the future take a different approach. But this will assure you of a very solid understanding of the process from taking the phototgraph through printing.

At this stage a good shot of whiskey will help Then you come back for more

Bob H

So here is the good news. After managing to struggle against the spread sheet I was using for a few hours, and finally scrapping up my own graph, plus doing it by hand on some graph paper, I have one of the numbers I was searching for.

The bad news is - the number I got is too low.

What I'm trying to do is to determine whether I've reached the "proper" development for this film/developer/process.

According to Kodak's sensitometry guide, in order to determine whether I've "properly" developed the film I must:

1- find the point along the curve that is .1 above dmin. (on my curve that's going to be something like .30, since my dmin is practically .20)
2- mark that point on the curve "A", and see where it is on the exposure axis. Note that exposure.
3- count over from that exposure 1.30 log exposure units.
4- go up from that point on the axis until you hit your curve again. Note the density units at that point. Mark it point "B".
5- using the density measurements, subtract A from B. This number should, if I've developed the film properly, be .80 +/- .05

That's where things fell apart on my process. When I do the math I'm getting .68 units difference in density between points A & B. i.e., my film is still a little bit under developed.

Kodak cautions that this must be gotten right before trying to figure out exposure index. (I'm not exactly sure why... after all, if I were doing testing by shooting a bunch of zone 1 sheets, they'd develop quite the same whether at 5 min or 6 min of development...)
Any way, I'm not about to jump off the deep end and start deviating from the prescribed course of action (prescribed by the manual on sensitometry), after all, I've come thus far, and once I've worked my way through it once I'll feel more confident about potential end runs on the process.

So, next up (in a day or three) more development testing... I'm at 5 min now... I'm guessing that I should try 5:30, and 6:00, and ..... it seems like a small bump in density that I'm looking for, I don't imagine that I'll need to go a full "stop" more development to get there. No? Yes? Maybe?

Um.. maybe it will help me if I pull some numbers for Gamma, and Contrast Index, and Average Gradient just to go the full Monty.

Here are the numbers for the three calculations:

(1.79 - .38)/(3.66-1.16)=.56 Gamma

(1.55 - .05)/(3.66-0.0)= .41 Contrast Index

(1.79 - .18)/(3.66-0.0)= .43 Average Gradient

now.. the manual does not give me "target" numbers for these measures..

I would assume from the idealized example graphs that these numbers should be something like this for "perfect" negatives.

Gamma - 0.63
Contrast Index - 0.61
Average Gradient - 0.51

Does anyone have suggestions as to what "idealized" numbers for those measures might be?


Um.. BTW - for anyone who actually reads the Kodak article... it has its fair share of typo's and screwed up diagrams. You have to actually be trying to follow what's going on to catch them... but they sure are there. In particular there is heinous one in the section on how to take the contrast index of the curve.

Ahh...
the spread sheet I was using to generate these curves... before finally deciding to hack my own. HERE (download will start automatically)

The thing I didn't like about that particular spreadsheet is that it does not give me actual exposure measurements at on the x axis.. but instead just step tablet wedge numbers. Without the actual measurements I couldn't do any of the math in my prior post.

Film speed?

Let's see...

Find a point on the curve that is 0.10 density units above D-min and label it A. Make a note of the log exposure at this point.

Click to expand...

That was at page 10. Go to page 11 and have a look:

Step 2 in the method is determining the film speed. The formula for speed is:

Film Speed = 800/(Antilog of A)

Click to expand...

Since your Dmin is 0,18, then A is at 0,30. This point had an exposure of 1,16.
10^1,16=14,45 That's the antilog of A.
800/14,45=55 That's the actual speed.

So, you're using a chinese film with a nominal speed of 100ISO and developed it in Dektol, a paper developer. Instead of a "proper" 100ISO you got 55. If you wanted "proper" speed, you should have used a "proper" developer. D76, like the pdf suggests. Anyway, there's nothing wrong with experimenting, that's fun. Why don't you shoot some at 50ISO and tell us your impressions? It's all great and scientific, but the print is what matters. If it works, it works. Keep us informed.

Oh, sorry, forgot to add that the neg could certainly be underdeveloped and you can increase the development time a bit. That should make your readings get closer to what's on page 10 (step 1). Regardless of that, the speed you're going to get won't be 100. Might be a bit closer, but I doubt it will get to 100.

Now, regarding gamma etc, it's all relative. Different light needs different contrast. Different tastes need different contrast. When targeting a specific contrast index, you affect the actual speed or development time or both. That's why I don't understand why point B should be 0.75 to 0.85 above point A.

A-Y,
Thanks for the posts. Lots to think about there.

Hm... your closing remarks about the points "a & B" peak my interest...
I was thinking that the measure they were indicating was meant to measure how much each tone is being expanded by development, and that in a given "scene", the tones at those two points should be roughly .8 density units away from each other. ( I can imagine a lab scenario where one might try to mimic the difference of tones on a gray card to the difference of tones measured in the densities of the neg... but ... this is a severely uneducated guess )

As for the ISO - thanks for the math, I'll note it in the little Kodak booklet. My intention is to shoot this film some where around ISO 50. but I hadn't gotten to film testing yet.. so your numbers are a great reassurance that I'm already in the neighborhood that I want to be in. I don't understand one thing though - why "800" ?

The part where you talk about matching the contrast index by monkeying with the iso settings, dev time.. or both... those are the considerations that I can only hope to grasp, measurably, by jumping these hoops "by the book" the first time. And I stress.. the "first" time. Once the technique is known, then the relationships become more evident and reinforced. Eventually, the adjustments come more naturally, but I can only hope to get there by at first just becoming familiar with the "knobs" at my disposal. Someone else recently asked me why I choose to engage in processes that are so fraught with technical problems (and which have often kicked my butt!)... their recommendation was that I simply try something easier. I totally understand that impulse. My reply was that when faced with any sort of technical problem we have only two ways of tackling it - master it or befriend it (or quit). I prefer not to give up on the process so long as I feel I can still make gains in how well I can do my "job" with the materials. If, I said, I finally get to the point where I know that I'm doing everything in my power, to the best of my ability, to produce one result and continue to get another - THEN I'll either walk away or embrace the "glitch", the "flaw" and make it my strength. They are different kinds of challenges. One is a technical, and craft-like kind of problem, the other way is a problem of intuition and aesthetics (it's easier to make bad art than good art, and just succumbing to a messy technique does not make the work any better by default).

Really, I think there is a serious part of me that want to be as familiar with this process as I am with my camera.. as smooth with the chemistry and film as I feel when I'm under the dark cloth... just as able to improvise and achieve the desired ends after the exposure as I am when connecting with the scene I'm photographing.

Prints prints prints....

I don't have any prints of these negs yet, but I have scanned one on my flatbed.
It's an absolute miserable scan. The glass needs to be cleaned and it was scanned on reflective, as the scanner can't handle film this size...
yada yada... Prints should start to happen this next week.



This neg is one of 50 ish I've shot as part of a photographic project I'm working on.This scan turned out terribly flat... I'm assuming because of the way it was captured on the scanner (reflective mode). Makes me all the more anxious to get to the lab and make some contact prints of these...

Um... I'm hatting that backdrop in the pic above ...
hmm...

Hmmm, I just reread some parts and I might have made wrong assumptions... oops!

We put point A at 0,1 density above Dmin. Ok, part B is 1,3 units to the right on the X axis. Because of the fact that 0,3 units is 1 stop, that gives us, as a matter of fact, that points A - B are 4,33 stops apart from each other. Point A will be featureless black on a print. I assume that point B should be medium gray. If that's correct, there should be a point C, 2,6 units to the right of A, or 8,66 stops apart.

Some time ago, I started a thread about characteristic curves and the usable density range of a film. The reply was that if using a condenser (enlarger) 1,3 units on the Y axis (density) is what is usable. If using a diffuser, then a bit more, like 1,5 or 1,6. So the "proper" difference between points A,B being 0,8 could be the diffuser scenario. It starts making more sense, doesn't it?

So your statement "I was thinking that the measure they were indicating was meant to measure how much each tone is being expanded by development, and that in a given "scene", the tones at those two points should be roughly .8 density units away from each other" seems to be correct! What's more, the formula that calculates speed needs as a prerequisite the 0,8 density units separation. Remember, it's 800/antilog(A) when using millilux and 0,8/antilog(A) when using lux...

It seems I made wrong assumptions previously, mea culpa!

Finally, judging by the scan, the result so far is not bad at all. It doesn't look terribly flat at my monitor. I think it's ok.

It would be nice to see the negative. Is there adequate detail in the dark areas (like the hair). If so, then your EI is probably OK. In terms of which contrast index or which gamma to use, that is the part where you need to find a "personal contrast index" because it will be based on your enlarger head, your enlarging paper and paper developer. You can do the paper curves to and match them up to your negative curve, but the problem is the shoulder and toe of the paper curves are a little imprecise. One way is to make some prints and see which ones look best. Then look back and make note of contrast index the negative and use that as your standard.

If you print with MG paper there will be a large range of acceptable contrast indexes that will be printable (ie from 00 grade to 5 grade). What you will do is decide what you like best. A thin negative printed in the 3-5 grade, a medium negative printed in the 2 range or a contrasty negative printed in the 00-1 range. Matching up the negative to paper curves can tell you which of those produces less distortion of tonal values (see the second example in Steve's post (there was a url link here which no longer exists)) but what would be important is which gives you a 'look' that you prefer.

For example I like about 0.65, but that only applies to my enlarger, paper, paper developer etc.

I'll have to admit I have not been following closely your method of exposure index calculation, so I can't comment. But just to emphasize, the only thing that matters in exposure is getting adequate detail in the shadows on your negative. Any way you can do that is a 'right' way.

it looks like you're almost there. Give your next film about 20 or 25% more development and see what CI you get. I shoot for about 0.60 as I use a diffusion enlarger, and if you are at CI of 0.41 I'd try 6.5 minutes for development time.

Next, you should to do some tests on your paper to figure out what CI your paper has. Same approach as with the film, but with a couple of differences on where you calculate the usable exposure range.

One you do these next few tests, then you're pretty much set!