Monthly Archives: December 2014

Understanding Film ISO Speeds

So you think you can dance?
It took me a while to comprehend ISO specifications while shooting and developing film. So, I thought I’ll give you some pointers that might be useful.

Films are rated at ISO speeds by manufacturers (there are exceptions). For example, KODAX TMAX TMX is rated at 100 ISO, KODAK TMAX TMY is rated at 400 etc. What this means is that the chemical density/composition etc allows the user to assume that eg for KODAK TMX the ISO is 100 and this can be used to calculate aperture and shutter speed settings for a given scene.

Now while developing, by changing development times you can actually change the Exposure Value on the negative (to a certain limit), as if the ISO of the film was different than what it was shot at. Of course, this is confusing.

Let’s try an example:
Using a light-meter, I metered a scene to be EV 10. I have KODAK TMX (ISO 100) and the meter calculates f-stop and shutter speed values as f/4, 1/60s (EV 10) for ISO 100. I go ahead and take the shot.

If I develop the film using 1:1 dilution of D-76 developer for 9.5 min, I’ll get the image on the negative as metered when I took the shot.
Keeping everything else same, if I develop this film for about 6 min the final image on the negative will come out about one stop underexposed … as if the ISO speed of the film was 50 (ISO 50, f/4, 1/60s = ~ EV 9).
Similarly, if I use undiluted D-76 for 11 min, the final image will look over-exposed by two stops (ISO 400, f/4, 1/60s = EV 12).

Practical applications?
Picture this (lol): It is overcast, you want to take a pic of a moving object and you have KODAK TMX (ISO 100). You meter the scene and get the EV as 10 (again??!!) which means f/4, 1/60s. You figure that 1/60s will definitely cause blur, and you need about 1/250s, plus your zoom lens won’t stop down beyond f/4 (now you know why f/2.8 zoom lenses are so costly :D)!! So, what do you do? Simple – go ahead and shoot at f/4, 1/250s (underexposing by two stops), and when you develop the film, look up the dilution/dev-time combinations for rating your film at ISO 400 and voila!!

What about the other shots on the roll that I shot at ISO 100? Go figure!

Case Study: Did you know that KODAK TMX TMZ P3200 was not rated at any specific ISO by Kodak? You can use (shoot/develop) it at ISO 400/800/1600/3200 (some have got good results with 6400 also!) … The P inย TMZ P3200 stands for Push, and that means more internet research for you ๐Ÿ™‚

Consideration: There are trade offs with graininess and contrast as you push the film during development.


Developing Black and White film

Easy … only two chemicals required … ๐Ÿ™‚ …

First thing’s first … 35 mm film needs to be rewound into the canister … 120 film will wind itself on another spool – just be sure to secure it tightly as soon as you unload it from the camera.

(Don’t) Let the light from the lighthouse shine on me!!
Loading the film onto a developing reel is the first step – and the only step that requires some practice and getting used to because you have to do this in complete darkness!!. I use Stainless Steel reels for both 35mm and 120 film – you may prefer plastic ones, and each has its pros and cons. After this, simply drop it into the developing tank and secure all lids. Done!! Lights, Camera, Action!!

Who let the dogs out?
Mix the developer and fixer in the recommended proportions with water (which should be at the desired temperature, in line with the chemical proportions) – this is of course subject to the ISO desired for developing the roll and I’ve covered this is another post. Don’t worry too much about controlling the temperature of the chemical mixtures during the whole process – just make sure there’s no drastic change – work in a closed (bath)room!

Shake that thang!
Both the developer and fix mixtures need to be agitated periodically while in contact with film emulsion. Some do it for 10 sec every minute, some do it for 5 sec every half-minute – I’ve done it both ways. Doesn’t really matter as long as you do it periodically (and slowly!!) to refresh the chemical in contact with the emulsion.

Somebody stop me!!!
A lot of purists will tell you that you need a Stop Bath after the developer, but then a lot of impurists (:P) will tell you that they’ve used plain water and that works fine as well. I use water at the same temp as the mixtures.

V for Victory! … Also for squeegee ๐Ÿ™‚
When hanging the developed negatives to dry after the final wash, just use your fingers to gently wipe the film.

Be sure to check out all the great videos on YouTube. Enjoy!!