Use of color analyzers / Wallner CA 904m

[Roger Vadim]

Hello!

I've posted this question in the other Darkroom Forum here, there was no response, so I try it here and ask a little different.

I recently purchased a Wallner CA 904 m color analyzer/ timer without a manual.

It's a well done old school piece of gear, and I wonder if you can use it for B/W evaluating time/ gradation, or as a workaround instead a densitometer.

I don't do color work in the darkroom, and I'd like to use it as a darkroom lightmeter, but I don't get to understand that thing. The timer works nicely, but the times are logarithmic (?) and not linear. How does one work with these intervals? And is it possible (if I will learn to know how to use it) to use it to evaluate time and gradation? Does one meter the light or the dark parts of the neg? how about VC, and the color ? :confused:

Questions over questions,

Any hints very welcome, thanks
Michael

[AJ Edmondson]

Roger... it has been a long time since I have worked with one of these but as I seem to recall each "step" or doubling was intended to increase - or decrease - by one zone. There was a lamp (in one arm of a Wheatstone Bridge) which was adjusted to illuminate at a specific "tone" in the image (by means of a Rheostat). Thereafter the adjustment was by means of the timer dial and the result could be interpreted as density changes.
Sorry I can't recall the exact sequences or terminology and I will search through my old files because I have the instructions for the B&W unit somewhere (have never seen the color unit) but the B&W units were well-made, useful devices.

[Roger Vadim]

AJ, right, there is a row of five LEDs, ranging from red to green and back, like a light meter in an old SLR. You can somehow calibrate for different papers with a wheel labeled "paper sensitivity" from 0-99: that also changes the reaction of the LEDs.

So the procedure might be: calibrate your paper from a known print on a certain zone of gray. If you then change the size of the print (or take another negative) you can adjust via the time wheel.

I figured out that if the button on the "cell" is on white, this procedure works. The main drawback: It only works (as far as I found out) with white light, once I dial in some magenta for the VC paper, i get really weird readings. that makes the whole thing quite useless because I prefer VC paper... might a green filter work?

The other thing is that the unit is extremely sensitive (which is a good thing I suppose), so its quite tricky to decide on a value of grey in the picture: so back to eyeballing again... (which I wanted to avoid with that thing...

Still unclear: Does it makes sense to take the lightest or the darkest part of the neg?
+
The timer readings are, as stated not linear. They read like that:
1 - 1.15 - 1.32 - 1.52 - 1.75 - 2 - 2.3 - 2.6 - 3 - 3.5 - 4 - 4.6 - 5.3 - 6.1 - 7 - 8 - 9.2 - 10.6 - 12.2 - 14 - 16 - 18,5 - 21 - 24 - 28 - 32 - 37 - 42- etc...

Could it be that this represents 1/5 zones? Each Zone doubles the exposure, right? In between are 4 increments... My math is not that good, can somebody with superior knowledge in the zone system and higher mathematics please elaborate that? ;)

Thanks for the help, there is a light at the horizon!

[ic-racer]

?
+
The timer readings are, as stated not linear. They read like that:
1 - 1.15 - 1.32 - 1.52 - 1.75 - 2 - 2.3 - 2.6 - 3 - 3.5 - 4 - 4.6 - 5.3 - 6.1 - 7 - 8 - 9.2 - 10.6 - 12.2 - 14 - 16 - 18,5 - 21 - 24 - 28 - 32 - 37 - 42- etc...

Could it be that this represents 1/5 zones? Each Zone doubles the exposure, right? In between are 4 increments... My math is not that good, can somebody with superior knowledge in the zone system and higher mathematics please elaborate that? ;)

Thanks for the help, there is a light at the horizon!

Zone = Stop. It is a 1/5th stop sequence. (Search for "F-Stop Printing" for pages of threads on that topic :) ).


You are 99% there if you are getting density readings.

You goals would be twofold. 1); get the density range and 2) determine exposure

Personally I'd forget about 2) and do test strips, but once you have the density range you can use that to help select your grade you want .


Yes, avoid measurements of the negative with anything other than white light, even though you may be multigrade printing.

[Roger Vadim]

everything starts to make sense now...

Couldn't I use it as a sort of sloppy densitometer then? base+ fog is one reading, and the negative with zone one should have 1 stop more exposure, ie. 5 clicks on the timer. same for zone V: 4 stops more on the scale.

The thing is really well build and if I start to understand it better works it could be a nice tool for testing films, right? 1/5 of a stop/ zone should be precise enough. It seems to be quite linear, if I close the aperture 1 stop it corosponds with 5 increments on the dial...

Any comments on that?

Thanks IC-racer and AJ, this was really helpfull!

Michael, just starting to see the light

[AJ Edmondson]

The B&W model I have is also well-built and, without the LED's appears similar in design. Generally, the "best practice" in an analytical mode seemed to be in selecting a dense portion of the negative which you decided should exhibit some texture (as a highlight) in the print, adjust time/aperture and measure the shadow area, again balancing the bridge circuit and determine log range to assess paper grade.

[ic-racer]

I forgot to add that it also can function like a densitometer to check film development. So if you negative range you measure is greater than your softest paper will handle, then you know to use less negative development time for similar scenes in the future. And vise-a-versa.

Personally I don't think devices like that really help that much in most darkroom work, but if you do go to the effort to figure out how to use it and really understand what it is doing you will be way ahead of most others when it comes to understanding development, exposure and contrast.

[Roger Vadim]

Hello all,

yesterday I finally found the time to do some prints, and found the device rather fiddly to evaluate the paper grade. the sensor is extremly sensible, and the questions where to place the sensor and then evaluate the negative is tedious. I am not that bad in evaluating by looking at the neg anyway, so I think I'll skip the whole sensor routine...

But:

the non-linear scale on the timer is really usefull for me: to think in increments of stops seems so much more photographic. For instance: if I decide that I want the skin tone half a zone darker, i just dial that in.

I hear everybody say: you can do that with a bit of simple math, but its really convienient to have it directly on the timer.

But I've got one more question: Is the tonal scale of the paper roughly the same then with film? Around 8 stops? sory for the stupid question, but I do still struggle a bit with darkroom math;)

Thanks for your help, still finding out a personal technique and a way to use that thing properly,
michael

[ic-racer]

But I've got one more question: Is the tonal scale of the paper roughly the same then with film? Around 8 stops? sory for the stupid question, but I do still struggle a bit with darkroom math;)


Depends on the grade of paper.

Iso (R) values of paper grade are determined by the paper range.

Iso (R) = range in stops x 15

So, a paper with Iso (R) of 120 will render 8 stops of input density range

[Ivan J. Eberle]

I'm not familiar with this device but I do have a Jobo ColorStar that came without much of a manual. I was using it for color, Ilfochromes and RA4, and found it useful mostly as an infinitely adjustable timer and for re-calculating exposure with filtration and enlargement changes. As I got more familiar with it I found it to be a fairly decent substitute for a densitometer, particularly when making contrast masks.

It's necessary to initially dial in the enlarger/exposure/filtration/bulb/paper pack/development process manually. Once done I replicated the enlarger settings, used these settings as a baseline, started taking readings and making careful notations. It all fell into place. The analyzer was often a real useful time-saver (not to mention paper-saver).

[Roger Vadim]

Really great input here, thanks everybody, there is a light (at the end of) the darkroom...

Ivan: these where exactly my thoughts in getting familliar with the device, although using it for B/W: using it as a densitometer plus helping me to evaluate the amount of +time for dialing in VC filters, i.e. yellow and magenta. This seems to work, although I am a bit suspicious about the color (esp. magenta) changing the reading. I need to do more testing with it.

IC: thanks, very helpfull! But how do I know the ISO of my paper?? Sorry, lots of silly questions - but already by now my darkroom skills are getting better, i.e. more systematical!

Cheers,
michael

[ic-racer]

IC: thanks, very helpfull! But how do I know the ISO of my paper??


The paper data sheet should say. There is a rough conversion, but I can't recall where the table is. Something like 100-120 ISO(R) = grade 2 and so forth.

Also, you can test paper by contact printing with a 21 step wedge. Leave out the first off-black and off-white steps and count the number of grays in between. Multiply that by 15 and you have the ISO(R)

The 21 step wedge has 1/2 stop increments.

I made an error earlier, because if you want to speak in terms of FULL stops then the conversion from ISO(R) to full stops is:
ISO(R) = range in full stops x 30

What I had previously posted was for half-stops.

[ic-racer]

Iso (R) = range in [1/2] stops x 15


CORRECTION:
Iso (R) = range in FULL stops x 30

[Roger Vadim]

Great! I did a bit of googling and found the datasheet with ISO (R) for one of my papers (Fomabrom Variant III), and it says for example: ISO (R) 110 at grade 1 (Ilford filter).

(Data can be found here: http://www.fsdistribution.biz/index.php?l=foma&id=f111)

This is very helpfull indeed. This means if I found a range of five stops in my negative I should use:

5x30 = ISO (R) 150, means grade 00.

That would mean a good neg to print on Grade 2 should have a range of:

100 (ISO (R) grade 2) / 30 = 3,33 so roughly 3,5 stops, measured with my device...

Ok. I'll do some measurements. This is interesting. I never thought B/W paper has that small density range.

cheers,
michael

[ic-racer]

Great! I did a bit of googling and found the datasheet with ISO (R) for one of my papers (Fomabrom Variant III), and it says for example: ISO (R) 110 at grade 1 (Ilford filter).

(Data can be found here: http://www.fsdistribution.biz/index.php?l=foma&id=f111)

This is very helpfull indeed. This means if I found a range of five stops in my negative I should use:

5x30 = ISO (R) 150, means grade 00.

That would mean a good neg to print on Grade 2 should have a range of:

100 (ISO (R) grade 2) / 30 = 3,33 so roughly 3,5 stops, measured with my device...

Ok. I'll do some measurements. This is interesting. I never thought B/W paper has that small density range.

cheers,
michael


Yes, if you look at a typical H&D curve, you will now appreciate that since the slope is less than unity (usually around 0.6 to 0.8) the excersion on the Y axis is going to be less than that of the X axis. So the density range of the negative is the Y axis excersion, and it is indeed less than that of the original scene.