Designing an experiment and choosing an appropriate densitometer

[iandvaag]

I'm in the process of designing a little experiment to learn about reversal processing black and white film. I've read an awful lot online, and for many months I was producing what I thought were satisfactory slides. I'm a contributor to a traveling folio which exchanges medium format stereoscopic slides, and someone included a DR5 slide this time around. After seeing this slide and comparing it to slides produced in my process, I realize that my dMax is severely lacking.

I've thoroughly read Haist's chapter on reversal processing, and now I'm ready to experientially learn what he describes. I've settled on Delta 100 for economy and to eliminate the potential "fade problem" with Pan F (what I've previously been using). I've ordered some chemicals to mix up a few different developers Haist recommends. My main variables will be amount of thiocyanate in FD, time/dilution of FD, and exposure index. After realizing that I am not very capable of discerning "success" with my eyes alone, I'm looking for a quantified way to measure my results.

Can anyone recommend an appropriate densitometer that is available at a reasonable price? I currently see on ebay the x-rite 810, 310, the Macbeth TD102, TD404. What should I look for? Also, what is there to consider about a Stouffer step wedge or sensitometer -- does one have an advantage over the other? I'm planning to shoot some photos at different EIs, but I thought it might be informative to generate and compare HD curves.

I'm open to any suggestions about the experiment's design. Presuming I'm able to learn something by the end of the summer, I'll post back with results.

 

[Mr Bill]

Also, what is there to consider about a Stouffer step wedge or sensitometer -- does one have an advantage over the other?

Hi, this question suggests that you could use a quick primer on the subject. A sensitometer can put a range of exposures onto a film or paper, but the typical sensitometer is, at its heart, simply a well controlled light source with, effectively, a "shutter." Generally the (common) sensitometers produce the "range of exposures" by passing their light through something like a Stouffer step wedge. For example, if you were to buy an EG&G sensitometer it would typically have some sort of step wedge taped on top of the sample holder.

If you wanted to only purchase a step wedge, then you have to supply the shuttered light source. As an example of DIY, you might go into a darkroom and hold the step wedge against the film with a piece of glass. Then you expose the sandwich in some way. You might, for example, fire a small flash unit set up to give consistent exposure across the wedge. It's a good idea to use some sort of holding fixture so that all exposures are consistent. You would ideally want the sensitometric exposure to be similar, in both exposure time and "color" of light, to what you use in your photography.

Ideally you'd like to know the exact light power your sensitometer (or flash unit, or whatever) is delivering to the step wedge. But unless you have it calibrated at a testing lab, you probably won't know. But you can test nearly everything you need using relative light values - all you are missing is the ability to assign an exact film speed.

 

[Mr Bill]

Can anyone recommend an appropriate densitometer that is available at a reasonable price? I currently see on ebay the x-rite 810, 310, the Macbeth TD102, TD404. What should I look for?

I just don't have any idea of the current market, but here's a few details. The most common units, Macbeth and X-rite, came with the capabilities of both color and "visual." Some color units are for slides, some are for negatives; you probably don't care since you're only interested in the visual setting.

I would feel comfortable with just about any "later" model Macbeth, by which I mainly mean that the display is not a dial or "nixie tube" numeric display. I'm not saying that these are "known bad," just that I'd avoid them if possible for various reasons.

In the X-rite line, the 810s were also fine units.

One thing about the Macbeth units is that they could typically be used with either the standard 3mm diameter measuring aperture, OR the accessory 1mm or 2 mm aperture (IF you have them). X-rite, as far as I know, only came with 3mm.

I'd say, in any case, to make sure that whatever you get comes with a working lamp (not burned out) and a calibration check plaque. If not, I think you can find what you need, but it's easier to just get a unit that has them.

As a note, if you photograph a Macbeth ColorChecker as part of your testing, it was designed so that a closeup photo on 35mm film gives test patches large enough to read with the standard 3mm aperture on a densitometer.

 

[Mr Bill]

After realizing that I am not very capable of discerning "success" with my eyes alone, I'm looking for a quantified way to measure my results.

Sorry to say, but I think that your eyes will have to be the final judge of "success" or not. But the sensi testing is a great way to study the effect of variations in your process. And when you eventually get the visual results you want, the sensi wedges will give you baseline measurements for reference should you ever need to troubleshoot your process or do further testing.

Best of luck to you.

 

[Nodda Duma]

I'm in the process of doing something similar for my hand-coated dry plates. In my case, I'm trying to determine the equivalent ISO rating and whether or not the coating is too thin. I acquired one of those Macbeth TD-102s off eBay (I'll need to get it working...shouldn't be difficult, they are not complex) and I also obtained a Kodak No. 21 Step Tablet. That and my spot meter which measures EV should be all I need.

Final verification (a.k.a. "sanity check") will be to increasingly expose sections of the plate to see what exposure gives the best image...just like what's done for prints under the enlarger.

I'm close enough that I can make good prints off the plate, just want to ensure I know exactly what it's doing.

-Jason

 

[iandvaag]

Thanks so much for both of your responses.

Re: Sensitomter vs step wedge
I'm mostly interested in relative exposure, you're right. It might be interesting to test absolute film speed however. Since I'm a hack who can't afford to buy a sensitometer and have it properly calibrated to determine film speed, I imagine I could use a flash unit at a fixed distance to determine absolute exposure in lux seconds and expose a film strip with step tablet atop it.

Most of the densitometers on ebay are not the traditional looking single probe densitometers, they are quality control strip reading densitometers that read a film strip exposed in a particular sensitometer. I gather that these densitometers would not be particularly suitable for my use.

Does anyone know about Tobias transmission densitometers? There is a TCX-S on ebay right now that's not too pricy.

As you both mentioned, visual assessment of actual photos on the film will have to be the ultimate judge of success, but it would be nice to compare quantitatively as well.

 

[Bill Burk]

Mr Bill and Nodda Duma,

Your answers are concise and clear... I've got nothing much to add since you covered it well...

The Stouffer transmission scales and Kodak step tablets serve multiple purposes. As Mr Bill said, one of these and a light source gives you a sensitometer.

Nodda Duma hinted at the idea, that you can use an ordinary light meter as a densitometer. Even an old GE lightmeter with a piece of cardboard that has a hole punched in it can do the job. To see how good a job, you can try to read those transmission step tablets, after all you should get readings that match the nominal or calibrated scale.

Stouffer sells calibrated step tablets for not very much more than uncalibrated ones. Uncalibrated ones cost about the same as a roll of film. So there's not much money involved. A calibrated step tablet is the same as uncalibrated... the manufacture uses a good "calibrated" densitometer to read it, and they wrote the numbers on the package. For example I have a calibrated T2115C which has a scale series nominally beginning 0.05, 0.20, 0.35, 0.50 etc. My calibrated step wedge came in a package with these numbers written on the package... .05, .19, .34, .49.... etc. It's the same scale and package that you would get with their T2115 which comes with blanks. For the calibrated version they just wrote the numbers on the package, and wrote "C" on the package and on the step wedge itself.

When I take readings from the calibrated step wedge on my own old Macbeth TR524 (has both reflective and transmission heads), I get pretty good readings +/- 0.01 over much of the scale but near the higher densities it starts to be +/- 0.02 and near 3.0 I am off by +/- 0.04

 

[Bill Burk]

I'm mostly interested in relative exposure, you're right. It might be interesting to test absolute film speed however.

With a stable, repeatable light source and the graphed results of several tests (assuming one of the test results will meet the ISO contrast parameters), you can get a decent estimate of the actual amount of light, by working backwards... because when fresh film is developed to ISO contrast parameters, you will very likely achieve that film's rated speed, which would give you a benchmark for the exposure axis that you can draw on the graph of the characteristic curve. Supposing the light source remains stable, that graph label will become your master graph for all your future tests (until some circumstance causes you to doubt the benchmark).

 

[Luis-F-S]

I'd stay away from McBeth Densitometers, most are over 50 years old and way too old. In the current B&W units, I'd look for an X-Rite 301 which is fairly common, can usually be purchased for under 2 bills, and the only B&W unit that X-Rite will still support. Try to get one of the single button ones as those are the most recent ones. That with your calibrated Stouffer step wedge and you're good to go!

 

[iandvaag]

Thanks for the advice. I'll have to keep looking as all of the 301's that I can find right now are $500 or more.

Does anyone have experience with Tobias densitometers? I'm not sure how much more I'm willing to pay for a 301 considering that getting it serviced will likely cost more than another unit.

 

[Luis-F-S]

If you get one in working order, you won't have to get it serviced. If you look at sold 'Bay listings, the last 3 sold for under $200. I've bought two very recent ones, I paid $350 for my first one, and $210 for my second one. There's one right now with a fairly late Serial # starting at $99 with no bids on it and 23 hrs to go!

 

[iandvaag]

Hmm. I can't seem to find it, maybe since I'm in Canada, eBay.com doesn't show me listings that won't ship up here. Can you pm me with a link to the auction?

 

[Bill Burk]

iandvaag,

Do you have a light meter/spot meter/enlarger meter?

The only thing a "real" densitometer offers over a home-made contraption is resolution and accuracy. You might be able to cobble something together with things you find at home.

 

[iandvaag]

I have a Gossen Luna ProF (reflected/incident) lightmeter. I'll have to look into it some more before I can ask informed questions on how to put something together. I'm considering a light meter since I anticipate doing a good number of experiments in the future, and eventually hope to make emulsions (one step at a time).

 

[sfaber17]

A Darkroom Automation meter with a step wedge and enlarger will work, and be as accurate as an xrite densitometer. You can still buy them new for $100 or so plus you have the bonus of having a nice enlarger meter. You can use an enlarger as a light source. I even use it to expose film as a sensitometer for 3 seconds. Perhaps there are reciprocity issues but you can still get a lot of good info that way. An xrite is more convenient as a densitometer though. I like the color versions 310 which is good for negative color film, or a 309 would work fine for b&w with the bonus of a UV channel.

 

[Bill Burk]

There is a darkroom enlarging meter attachment for the Luna Pro, I assume it would fit the Luna Pro F.

That would be a great choice.

In order to measure density with such an attachment, you would set the test negative in your enlarger (It could be the step wedge for practice readings).

Enlarge onto the Luna Pro with Enlarging attachment. The reading of a clear section or without negative would be your "zero" and then you put the sample in place.

The difference in f/stops from one reading to the next can be computed to be the density in 0.3 units per f/stop reading difference. (Thus a density of 0.10 would show on the Luna Pro dial as a 1/3 f/stop drop in the needle).

Flare would be "an issue" when using an enlarger to measure densities. But you could learn to live with it.

Density readings of 0.1 precision are suitable for amateur photographic purposes. When you consider how much tolerance exists in black and white, negative-positive processes, you can appreciate that 0.1 precision is good enough to learn the science and control the process. A "real" densitometer could get you readings with 0.01 density precision.

 

[MartinP]

If anyone makes a setup using a flash-unit as a light-source, be very careful of the repeatability. I recall using a Bowens Ilumitran (spelling?) many decades ago, that needed careful watching. The flash would vary by more than a quarter of a stop between each of the first two flashes and the remainder. As the foibles of that particular device were known, we would pop it manually a few times before starting duping. The repeatability depends on the state of the capacitors and voltage circuitry, which wouldn't be a problem in normal 'auto-flash' usage but clearly can show up when looked at for some precise purpose.

 

[Bill Burk]

Sensitometer-wise, the EG&G has been remarkably consistent. Most of my curves "line up" on paper.

When I tried "Electronic Flash as Sensitometer" experiments, I wonder if I made a lucky choice to use my old Vivitar 283 with its variable output option. By "under running" the flash, I may have avoided the inconsistent output of a full discharge from most other flashes in "Manual" mode.