What is the standard calibration method for 35mm film?

[Andrey]

All I have is medium and 35mm cameras. If I shoot with those and want to calibrate my film I'll have to waste a frame per reading. I'll also intoduce lens flare and aperture inaccuracies into my test.

If I were to use a step tablet and contact print it on film, then I'll have reciprocity failure and the results are useless.

What's the standard way to do it? What machine you use to expose your film when you're trying to come up with a density curve?

Thanks

 

[ic-racer]

All I have is medium and 35mm cameras. If I shoot with those and want to calibrate my film I'll have to waste a frame per reading. I'll also intoduce lens flare and aperture inaccuracies into my test.

If I were to use a step tablet and contact print it on film, then I'll have reciprocity failure and the results are useless.

What's the standard way to do it? What machine you use to expose your film when you're trying to come up with a density curve?

Thanks

Iif you are interested in determining ISO you would need a calibrated sensitometer. (But its easier to just look at the number on the box )

A makeshift sensitometer or an uncalibrated sensitometer is very useful for making film curves to understand gamma and development time.

In terms of exposure index, there are numerous methods. Easiest for me is to shoot a target and place it at zone I. Check the negative for 0.1 log d (1/3rd of a stop) above film base + fog. You can use a densitometer or a light meter to check the processed film.

Here is a pair from Tobias. Sensitometer (to expose the film) on the left and densitometer (to read the processed film) on the right.

 

[Andrey]

I can't buy two devices. lol It's cheaper to waste a couple of rolls of 35mm for calibration purposes.

I think I'll just expose the film with my camera and lens and then mail the film somewhere where they have a densitometer.

 

[ic-racer]

I can't buy two devices. lol It's cheaper to waste a couple of rolls of 35mm for calibration purposes.

I think I'll just expose the film with my camera and lens and then mail the film somewhere where they have a densitometer.

That should work.

 

[jgjbowen]

I think I'll just expose the film with my camera and lens and then mail the film somewhere where they have a densitometer.

Richard Ritter provides this service. http://www.lg4mat.net/page8.html

Of course you could also order Bruce Barlow's "Finely Focused" book on CD. It includes the tools you need to do your own film speed and development time tests without a densitometer. www.circleofthesunproductions.com

Either one will fit your needs.

Good luck,

 

[Nicholas Lindan]

35mm cameras ... calibrate my film

If you contact a step tablet there won't be any problem with reciprocity effects if you keep the exposure at 1 second or less - a digital timer would be needed so you can have consistent exposure results. I would use a 4x5 step tablet (the best choice if you have a 4x5 enlarger) and contact a 5 inch length of film or use one of the long skinny step tablets and a 7" length of film. Both of these will provide density spots that are big enough to measure with a bench densitometer.

My method is to use a 35mm sized step tablet that I have mounted in a slide mount and photograph with a macro lens, bellows & slide duplicator attachment.

I take a whole roll of step tablet pictures and then develop the roll, snipping off a few frames every minute or 30 seconds and dropping the snippets in stop bath. Cutting ~3 frame snippets yields 12 different developing times. The act of lifting the reel from the developer, having it drain while I cut off a bit of film and then returning the reel to the tank serves as agitation.

Obviously a normal bench densitometer can't be used to read the resulting 21-step negatives because the density patches are just too small.

However, with an enlarging meter it is possible to make density measurements of the projected image. Using the enlarged negative makes sense as you are measuring the effective density seen by the paper in your enlarger, and this is the film curve you are really interested in knowing.

The Darkroom Automation enlarging meter has a special densitometer function that indicates density over base+fog to 0.01 stop/0.003OD. Once zeroed on the film base the meter displays density continuously. IIRC, the loyal opposition, RH, has a densitometer function in one of their 'analyzer' models that flashes a density number for a second or so when a reading is taken, but I am not familiar with it. It is possible to calibrate Ilford's EM-10 meter to a projected step tablet, however having done this I can't recommend the procedure - the experience was my motivation for designing the DA enlarging meter.

 

[RJS]

Mr. Lindan: Do you have any usable results for measuring density of pyro stained negatives with a cold light as the source? And also, I wonder what is the size of the sensor on your meter? I have long ago given up trying to measure the density of stained negatives using the cold light. Occasionally I try my old Weston densitometer which I calibrate against a Stouffer step wedge, but the wedge is not stained so it's a pretty useless exercise. None of it really matters as I have given up printing step wedges to go on the wall and resort to empiricism for film speed and developing times. Works ok but not very scientific. But a REALLY small sensor would be a nice thing.

 

[Nicholas Lindan]

... what is the size of the sensor on your meter? ... pyro stained negatives with a cold light as the source? ... old Weston densitometer which I calibrate against a Stouffer step wedge, but the wedge is not stained so it's a pretty useless exercise.

The sensor is square and 0.09"/2.3mm on a side. Since the meter works with an enlarger, the size of the effective measuring spot varies with the enlarger magnification and you can measure as small a spot on the negative as you wish.

For calibration with Pyro negatives you will need a step wedge on the same film and developed with the same developer as the negatives you are going to print. The easiest method is to simply contact a step wedge on your film and process in pyro. The resulting wedge will be the inverse of the original but should encompass the full density range of the film. Obviously the resulting pyro-wedge won't have the same even progression of densities but this really doesn't matter: what you are interested in is the relation between the meter reading and the resulting tone on the print and the actual density plays no part in this calibration.

The meter will do a reasonable job with some pyro developers and some enlargers right out of the box. You would have to judge for yourself how well it works with your enlarger and your particular developing regime and film.

The meter comes with a 30-day guarantee so if it doesn't work satisfactorily in your application you are only out the shipping charges. So far (famous last words) no pyro worker has returned a meter.

 

[Monophoto]

One of the potential hazards of becoming too enamored with the Zone System is that you end up doing nothing but testing, and never make any real pictures.

I've done Zone System tests several times with both my 35mm system and my 4x5. 35mm was simple and quick - set up a target, make a series of exposures, process the film, and then decide which exposure was correct. I tested for Zone I, and used a visual comparison device consisting of a small chip of neutral density filter material in a frame - I would lay the exposed/processed film on a light box, align the optical comparator on the film to cover the unexposed rebate/edge, and then decide which on which frame the exposed target brightness most closely matched the film base + fog + ND filter brightness.

Interestingly, in a number of tests (I must have done this 5-6 times), the tested speed always came out to be about one half the manufacturer's published rating.

The same process worked with 4x5, only it was slower because I had to expose several sheets of film with the darkslide pulled only half way (in order to have both film base+fog and film base+fog+ exposed target on the same sheet of film. To simplify the process, I assumed that 4x5 and 35mm were simlar, and started at one half the manufacturer's rating.

You also have to do a film development test, trying to achieve a Zone VIII exposure and judging that by making a contact print in which film base+fog produces the threshold maximum black, and then the VIII exposure is only perceptibly darker than the paper base.

The challenge is to simultaneously be disciplined and sloppy - disciplined enough to do the tests until you are convinced that you have an answer that is good enough, and then sloppy enough to assume that those results are dependable and you can then make real pictures with no further testing.