FAQ—Exposure
Exposure Part One
Let me begin by saying that I make no apologies for my bias towards craft, the craft of the image making process is as important as the idea behind the image, there I said it, all you post-modernists can just go to hell. I'll say it again, I give equal value to the idea AND the craft behind the construction of the idea.
Now, what has this to do with exposure? Well exposure underpins one's approach to the whole process, if you have an idea and want to express it using photography, you can either get a technician to expose your film or do it yourself. Again I am from the old school of, "I know what I want therefore I think I am best suited to executing my own ideas" - besides it's cheaper.
Anyone with a modicum of experience will know and perhaps understand that ALL LIGHT METERS READ FOR MIDDLE GREY. Your setting of the camera based around middle grey, determines the final appearance of the image in the print by the amount of exposure and development given to the image, which in turn is affected by the contrast of the scene and light reflecting back off the image. Give more light than indicated by the light meter, the final print will be lighter than middle grey, give less and it will be darker. However I have a rule of thumb, this enables me to 'print' the negative any way I want.
My rule of thumb for negative materials is - when in doubt over expose - so if you are caught short on location/holidays/miles from home play it safe and rate the film at least 1/3 to 1 stop over exposed. This applies especially to the wonderful and much misunderstood film developer Microdol-X™ made by Kodak™, where even Kodak™ recommends a one stop increase in exposure with all films.
Here are the numbers to work to when over exposing:-
- 400 ISO/ASA rate at 320 - 200 ISO/ASA - 200 MINIMUM if you use Microdrol-X
- 200 ISO/ASA rate at 180-100 ISO/ASA - 100 MINIMUM if you use Microdrol-X
- 100 ISO/ASA rate at 80-50 ISO/ASA - 64 MINIMUM if you use Microdrol-X
Please be aware here that I said negative materials, these are, black and white film, and colour negative film. Films such as Ektachrome™, Fujichrome™, in fact ANY film ending in chrome is a slide film and requires different treatment compared to negative materials [more on this in another article]. Once you are back in the safety of your studio/processing facility, some compensation can be made for the increase in exposure. The actual amount of compensation will depend on tests you have already carried out, and the amount of contrast in scene photographed, but as a start you can subtract about 10-20% per whole stop. My previous article on films and film developers has some more information.
The reason for this approach is simple, the primary agent that activates the silver halides in our film is - LIGHT. Anything that occurs post exposure only brings that physical reaction to a state whereby we can see the results and preserve them for a very long time. So NEVER rely on push processing techniques or speed enhancing developers to give you results that just do not exist on film. If you are like me and are interested in a 'finely crafted image' then you are probably are not interested in coarse grain, empty shadows or blown out highlights, using push processing techniques will give you these results, speed enhancing developers may also give these results.
Measuring exposure is something we rely on our light meters to do for us. Not a bad thing really however these items are 'mechanical' they simply respond to whatever it is that they are pointed towards. In return they 'weigh up' the amount of light and give feedback based on your chosen ISO/ASA setting, on where to set the camera. In a situation where there is a disproportional amount of one tone, as in a snow field for example, the light meter will give an erroneous reading. Knowing how to compensate is important, knowing how much to compensate is only achieved through thorough testing - several books on my resources page have in-depth discussions about this testing process.
Also the way that the traditional SLR built in light meter works is that it will have an emphasis on a particular area in the scene - often towards the centre of the frame- so if you have a situation whereby the sky forms more than 1/2 the image, again an erroneous reading results. Some argue for an expensive hand held meter that allows complete control, yes ultimately if you are serious about your image making this the way to go. However the outlay of this kind of gear can far outweigh it's use so simply being aware of the way a light meter works may be enough to improve your technique.
My tips for a better use of built in light meters in cameras are as follows
- When in doubt over expose your negative materials.
- In a situation where, the sky or foreground 'dominate' your composition, meter by angling the camera in such a way as to have a more average distribution of tones. Then recompose without changing the camera settings.
- If you can, go 'in close' and take a reading of the most important part of the scene filling the viewfinder with the subject, and setting the camera as indicated by the light meter, again leaving it unadjusted when you re-compose.
- In a situation that may never be repeated taking a series of exposures that over and under expose the scene by one or 1/2 stop increments may save your ass! Desperate and completely unprofessional though.
You will notice that I have not talked about digital cameras, this is because I am still researching the best way to deal with CCD's, anecdotally at this time negs that are destined to be scanned SEEM to require a density that is higher than those required for traditional wet darkroom enlarging, as well as a higher contrast.