Personal film speed tests

[davis1862]

I've got a few days off work this week and am interested in using it

to determine my personal EI. I've read about several methods of

conducting personal film speed tests. I'm curious, though, to hear

from users of this group on which particular tests you used to

establish your EI.

 

For what its worth, I'm using a Canon EOS Rebel with a 50mm 1.8 lens

and will be testing Ilford Delta 100. I'll conduct additional tests

later on other films.

 

Thanks in advance.

[jay_de_fehr]

Ken, testing for your personal EI can be as simple or as complicated as you care to make it, but before you get into all of the sensitometry and controls involved, I have a few questions that might save you some time and trouble. Have you shot Delta 100 with your Canon EOS Rebel with a 50mm 1.8 lens before? If so, what EI did you use when you did? If not, I suggest the following; shoot a roll of the Delta 100 at EI 100, develop in your developer of choice for the manufacturer's recommended time, or if you use a homebrew, for your best guess. Print the resulting negatives on your paper of choice, and assess the resulting prints for shadow detail and highlight density. Adjust exposure and development as needed. My experience has been that box film speed is very close with most developers, requiring only slight adjustments in exposure and development for optimum results. If you are determined to calibrate your process to within 1/10 stop or less, you will have to do a lot of reading, invest in a densitometer, and spend many, many hours, and many, many rolls of film to learn that that kind of accuracy is not practical with roll film unless you shoot the entire roll of film in identical lighting. You will probably be just as well off to choose your EI at random within +/- 20% of the box speed unless you're using a developer that deviates widely from the manufacturer's rating, like Microdol-X, or Diafine, and fine tune from there. Probably not the advice you were looking for, but accurate film speed determination is quite complex and takes into consideration every step of the photographic process, and includes every material and chemical in the chain, and in the end, is not really applicable to the common use of rollfilm. I suggest you use your free time to make photographs and save your testing to overcome actual impediments to your process. Good luck.

[trooper]

Barry Thornton's site has some interesting reading on this subject:

 

http://www.barry-thornton.co.uk/pfs.htm

[doug_harhai]

Ken--just an observation I made from a new book by Lee Frost, on Black and White photography. He says that he has never done an EI rating--he just goes by what the manufacturer says on the film box! When you look at his work it is hard to argue with him. I don't know that he will ever be considered a printer with the skill level of Ansel Adams, but neither will I, and his work is much better than mine. I have considered doing my own tests in the past but eventually thought otherwise--there are too many variables involved that I do not control consistently, as the first poster mentioned. FWIW, I thought that Barry Thornton's instructions were confusing, but the ones set forth in Kodak's "Advanced BW Photography" are pretty clear.

[andrew_limiti]

Ken,

 

If you have fairly well stocked library near you I suggest the book The Practical Zone System: A Simple Guide to Photgraphic Control by Chris Johnson. There is a good chapter on determining the EI of film which is explained in a pretty straight forward manner. I copied the chart he provides in the book, which is very helpful for keeping records of your exposures in a logical order.

[adrian_vincent_twiss]

Ken

 

There is another way. Cut your film speed by half (rate at EI 50) and reduce the development time by 25%. Once the film is developed make some prints on the paper of your choice using your standard printing method. If the shadows are not deep enough then your speed reduction was excessive and you should rate the next film at EI 64 or 80 depending on how grey the shadows are. If the highlights are difficult to print i.e. blocked out then you should reduce the film development time in steps of 5% until you feel they are right. If the highlights are difficult to print because they are veilled and grey and you need to use hard paper (around grade 3.5 to 4) then increase the development time in steps of 5%.

 

A little crude perhaps but within 2 or 3 films you should get your EI and development time locked down for your equipment and exposure methods.

 

Hope this helps.

 

Adrian

[don_karon1]

The speed point of film is (roughly) the exposure that produces a film density of 0.1 greater than fog + film-base density. It is not much affected by development and is almost exclusively controlled by exposure.

 

There's no printable detail down at this end of the density curve, just featureless black. In the Zone System this is where you want to put Zone I. You then adjust developing time to pin down the highlight end of the curve. Adams recommended aiming for a Zone IX density of 1.15 (this is N-1 development, which he prefered for roll film) for use in a condenser enlarger, a bit higher for a diffusion head. After fooling around with this for several years I believe he was right on the money with this suggestion.

 

The easy way to measure this is with a densitometer but these are costly. I suggest borrowing time on one at your local medical x-ray department. They use one to keep their x-ray films developing correctly. Look for a place that does mammograms - Federal rules require them to have and use a densitometer as part of their quality control requirements.

 

There are several other systems to measure density which are very tedious, subjective, and (in my hands, anyway) not very reproducible.

 

You can do it without any of this, just inspect your prints with a critical eye, identify the problem areas, adjust development and exposure to correct the problems. The ultimate goal is to make good looking prints. If the prints look right the numbers don't matter.

 

B&W film has a very large sweet spot. There's batch to batch variaton that is hard to control exactly. Film varies, it ages, the chemicals vary with time, temperature varies a bit even in a water bath, my agitation is not machine-like in its precision, etc. You are safe because there's quite a range of negatives that print well. Besides, you probably make exposure decisions that create bigger changes in the negative than film speed settings and developing variation.

 

I spent a lot of time chasing numbers. It was fun it its way. Currently, I check densities every now and then, but am (mostly) recovered from this.

[ray .]

I don't see how you effectively determine this in a few days by doing tests. Maybe you get an idea of it. Photographic printing is a subjective issue, it seems to me it's better to shoot real photographs and experiment with how variations of film speed affects their look. This can evolve over a period of years, and in some instances over a lifetime. My personal take is to do it more by feel. Numbers and densitometry charts might be useful at times, but have their limitations.

 

Much more influential on image quality and the look of the photo than whatever deviation you happen upon from manufacturer's recommended film speeds is the quality of light in the scene you photograph.

[ray .]

... For less forgiving films, such as color slide film, the issue of personal film speed is of course more critical.

[stephen_benskin]

IMO, most of the "personal" film speed methods just give a false sense of accuracy. Take for instance the method of stopping down X stops and opening up the lens of adjusting the shutter speed in small increments. First, how accurate is the f/stop? The f/stop indication is a mathematical value and not a tested value for that lens. You will need T/stops for that. Then there is the accuracy of the shutter. It may not only be giving you a shutter speed different from indicated, but the variance between different settings can be different.

 

Let's say you only change the f/stop. This method could eliminate the relevance of any practical difference between the f/stop and t/stop. You are, in effect, incorporating this difference into your "personal" speed. This is all fine and good only if you use this lens. Use another lens and you have a whole new f/stop, t/stop relationship which negates your test. Now, you have to do film tests for each and every lens. Also, are you really pegging 1/3 stop increments on the lens. Most lenses don't have click stops for third stops.

 

Then there's the shutter speed. You did all your tests using the same shutter speed. What about the other ones? Your test is only truly valid for that shutter speed. You will have to determine a personal film speed to each and every shutter speed in order to have absolutely accurate results.

 

Don't forget general testing variations. In order to eliminate a random variation from influencing the results, you will need to run dozens of tests and average the results for each and every step mentioned above. No body wants to do that.

 

And all this is an example of only one set of variables. What about the light source, color temperature, meter calibration, photo cell spectral biases, metering techniques, variations in emulsion batches, or dozens of other variables that may crop up under the testing conditions but will be different in actual use?

 

This is not to say that you shouldn't test. I personally have a sensitometer which I do my test exposes on. While it is more accurate than almost any other method, I know that there are so many other variables at work in real world conditions. Know the conditions, understand the realities, and see what works for you. Use the test as a starting point. Understand what film speed is and how it works. Understand the roll of film speed in relation to exposure. This is the best possible approach.