Film speed testing without a densitometer

[David Home]

Hi all.
I know this subject has been discussed before, but I am hoping to get some more specific comments.

I bid on a X-rite 810 densitometer this week on ebay and it ended up going for $500US.
Oh well, so much for getting a densitometer! I think this is pretty high a price for something I am only going to use occasionally. So I would like to consider the alternatives.

1) Stouffer 4X5 step-wedge from Bostick&Sullivan. Someone mentioned in an older thread using the Souffer on a light box and 'eyeballing' the test negatives to get a close match. Will this get me within 1/3 of a stop? What as the values of the lower steps of the wedge?

2) I have a corrected spot meter from Zone VI which is quite accurate and linear.
Could this be used to meter the negatives on a light table and be accurate enough?

3) Any generous lab staff or serious amateurs in the Toronto area that would let me use their densitometer? I am happy to show my appreciation with beer or butter tarts.

Any other methods please let me know. Thanks for your comments.
Regards, David Home

PS: I just thought that maybe a combination of 1 & 2 might work. This would use the light meter only to make comparative measurements and not demand absolute accuracy....

[ronald moravec]

You can pay someone to read a neg for you. Prolabs should be equiped. Unfortunately I have forgotten the required density reading for i stop above FB+ fog.

For decades I used a standard test target that consists of a color checker or grey card depending, a step wedge, a doll with pleated black skirt and linen white blouse. The print needs to show the pleats clearly and the blouse needs to show detail.

Film speed is detirmined by the fasted speed at which I can get a printable difference in the lowest darkest 2 steps. Development time detirmines if I get grey ( underdeveloped ) or featureless white lacking detail ( over developed) detailed whites.

Add some white and black clothing to the shot.

Remarkably it turns out to be box speed so I must be doing something right. The doll is rendered correctly also.

Keep in mind a 4x5 view camera focused on 8x10 area will have one stop underexposure from bellows extension with a symetrical lens. When you do an outside pic, it will be over exposed unless you compensate. Development time will be the same. 123 and 35 mm have less compensation required.

Less accurate, but go outside and do some white houses and car tires. Tites should be dark, but not as dark as shadows under the car.

My subject is studio strobe lit so it is available day or night, summer or winter and is always the same. It also works for color or digital with the color checker instead of a grey card.

Easy 1/3 stop accuracy.

[BetterSense]

I just use my eyes, and the following method:

Meter for medium grey, with your reference meter. Consider the indicated amount of exposure "zone 5". Make an exposure of a grey card.

Make a series of exposures with one-stop less exposure (zone 4 through -1 exposures).

Develop normally; when you are done, pick the sheet that shows the first hint of visible density compared to clear film. Zone -1 should be clear and zone 0 should be clear and if you have (printable) density on zone 1, your EI is pretty good. Pretty often, it turns out that zone 2 is the first negative that has any printable density on it, so I reduce my EI to 1/2 box speed.

I think zone 1 is supposed to be .1 log D above film base+fog.

[jeroldharter]

Try the BTZS approach:

• Adjust the light source on your enlarger so that a reflected spot meter reading at ISO 100 reads EV4 on a matboard on the easel.
• Place your film on the baseboard and contact print the step wedge on to the sheet film using an exposure time of 0.4 seconds on you enlarger timer.
• Process the film. Use multiple sheets, all exposed the same way, and develop for 4, 5.6, 8, 11, and 16 minutes.
• Send the film to Fred at the View Camera Store and he will do all of the densitometer testing for ~$50 and give you extensive film information using the BTZS plotter program.

[Brian Ellis]

The reason the x-rite 810 densitometer fetched such a high price is that it's a combination reflection/transmission densitometer. There's very little market for transmission densitometers alone these days because they were mostly used by labs that did film. But there's still a market for reflection densitometers because people who print digitally use them to create profiles and probably do other things.

If you only want a densitometer for film tests, you don't need a combination reflection/transmission densitometer, a transmission alone will do fine and you can get one of those for a whole lot less than $500. I think I sold my Macbeth on ebay for something like $150.

[BetterSense]

A transmission densitometer is also a very simple device to make if you understand the principle of densitometry and can solder. I have an accurate densitometer I made for less than 20 dollars, using a phototransistor and micontroller with LCD display. A simpler form would simply be a battery, phototransistor/photocell, pot, panel ammeter from radioshack, and calculator that can do logs. Extra points if you use a slide rule.

[Nathan Potter]

Phil Davis describes how to use a spot meter with a density wedge as a densitometer in his ever famous book "Beyond the Zone System". To summarize:

If you use a Pentax spot meter find an old 46 mm thread filter of some sort and smash out the glass. Buy an achromat of about 1.790 OD from Edmund Scientific with say about a 5 inch focal length. If lucky you can ram the achromat into the filter ring which then will screw directly into the Pentax front.

Next build a stand that will hold the Pentax directly over a light table with the lens exactly focused on the surface of the light table. When mounted the button needs to be depressed so that you can read the light intensity. I discovered a useful trick in actuating the meter. There is a screw in 1/4-20 thread at the base of the handle which holds a strap. If this is unscrewed the meter won't work - the battery circuit is disabled. The meter is enabled electrically thru the 1/4 -20 screw making connection between the outside metal base on the handle and the internal threads that it screws into. So -- I replace the 1/4-20 strap holder part with a longer brass 1/4-20 machine screw with a wire stub soldered on. Make sure the brass screw doesn't contact the bottom plate - you can wrap a bit of insulating tape around the screw to be sure. Now you can connect an external on/off switch between the brass screw and the bottom plate to actuate the meter as long as the regular button remains pressed. The new switch can be a momentary type that is attached to the stand along with the meter. My light table runs at about 16 EV brightness (164,000 lux) which allows me to measure logD 3.0 at about 5 EV without difficulty.

Some precautions in setting this up though. You want to read only transmitted light so work in a dark room.
Also as mentioned by Davis I cut an aperture on a piece of white cardboard slightly smaller than the width of the Stouffer step so as to see only that particular density on the reference wedge. The aperture also reduces scattered light entering the spot meter so provides increased accuracy. The white surface makes it easier to see where on the negative you are or what step on the wedge you are at.

Operationally you are matching the known density of the wedge to the spot on the negative that you want to measure. You can also do a crude interpolation when the two spots are slightly off and resolve about 1/3 stops. I found it desirable to toggle the meter with the external switch so as to not drain the battery in the spot meter. I would also point out that a calibrated Stouffer wedge is pretty darn linear but the spot meter exhibits a slight discontinuity at some midpoint (I forget just where in the scale). Overall this is makes a pretty effective densitometer as Davis suggests although I've been using such a device in my home darkroom long before Phil suggested it.

Nate Potter, Austin TX.

[domaz]

Vuescan has an option to "Toggle Densitometry Display" or something like that if you have a film scanner and Vuescan. After you scan you hold Ctrl and it displays the values as you hover your mouse over areas of the image.

[Ken Lee]

You don't need a densitometer.

Here's a brief article that shows you one method. In a nutshell, you try 3 different film speeds, and 3 different developing times.

[ic-racer]

For you "Zone I" test, put the negative over your standard reflected light meter's sensor and look for a 1/3 stop drop. That would be the 0.1 d negative.

If you are using 1.2 d for Zone VIII then then correct negative will give a 3 stop drop when placed over your reflected meter's cell.

In the mean time keep looking for a densitometer. I got 2 for $25 a few years ago.