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F-stop for ISO 100 film

Now my question to you will be... what if I use a ISO-100 film. Does the same trade apply for ISO-100 also?

I have a Canon EOS Elan IIE SLR and I am going on a vacation to Europe which will cover all the popular places around Europe. What film speed you would recommend considering most of the snaps will be taken in the day time during the tour. Also whether Fuji or Kodak will give more color to the photographs if you recommend ISO-100 film.

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March 21, 2001

The ISO rating of a film can be directly related to exposure settings. Doubling an ISO is the equivalent of a stop faster exposure. Cut the ISO in half and it's the equivalent of a stop slower exposure. ISO 100 film is two stops slower than ISO 400. This makes the trade-off of stops for shutter speeds shift by two stops compared to what I gave for ISO 400:

f/16 @ 1/125th
f/11 @ 1/250th
f/8 @ 1/500th
f/5.6 @ 1/1000th
f/4 @ 1/2000th

These are all within 1/3 f-stop under direct sunlight for a clear, sunny day (the f/16 sunny day rule) starting about an a half-hour after sunrise to about a half-hour before sunset. The test is sharp, distinct shadows. This rule is f/16 @ 1/(film ISO) for the shutter speed will get you within about 1/3 stop under these conditions . . . and you can trade shutter speed for f-stops as shown above.

If the subject is under an overcast sky or in shade, this must be modified for more exposure. Here are some guidelines for how much esposure to add to the "sunny f/16 rule":
+ 1 stop: Weak, Hazy Sun; shadows with soft edges (not sharp); distinct outline of sun
+ 2 stops: Cloudy Bright; no shadows; bright spot in sky at sun location but no distinct outline of it
+2.5 - 3 stops: Heavy Overcast; no shadows; sun cannot be located by a bright spot in sky
+3 - 3.5 stops: Open Shade; completely in shade (side of a building; etc.) under open sky
+4 stops: Deep Shade; in complete shade without open sky; under forest canopy on an otherwise bright sunny day.

Thus, if you were use f/11 @ 1/250th under direct sun on a clear day, you would use f/11 @ 1/60th, or f/8 @ 1/125th, etc. in "Cloudy Bright" conditions.

I would use ISO 100 or ISO 200 film if you intend to shoot everything, or nearly everything outdoors. Choice would depend on how wide the lens can open up. ISO 400 could get you into trouble with few shutter/aperture choices under "Bright Sun" with a clear sky. If your lens is fast enough, at least f/2.8, you can continue doing landscapes and architecturals (versus things like car racing) hand held even under heavy overcast. If you have a slower zoom (about f/4.5 or f/5.6 zoomed out), ISO 200 might be a better choice.

In ISO 100 color negative, my selection would be Kodak Royal Gold, or Fuji Reala. Both are extremely fine grained, general purpose consumer films with a some saturation. They both handle skin tones well.

I don't use much color negative any more except for portraiture and some shots for special applications; I've been using Kodachrome 64 slide film for scenic and architectural for some time. Film choice is very much a personal one based on subject material and what you want for your images. There is no truly right or wrong choice.

Hope this helps.

-- John

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March 21, 2001

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March 21, 2001

Now since I have a 3.5-5.6 USM V Lens I am little confused as where do I place this lens. Is it fast lens (as it is USM V) or not very fast(because it is f/3.5-f/5.6)?

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March 21, 2001

I agree with Jeff's advice to avoid running with no meter. This is how I use the "sunny 16 rule:"

a. Planning for a shoot:
Based on the anticipated range of lighting conditions, the most likely combinations of shutter speed and aperture can be determined in advance. If it's too restrictive, then a different film speed may be better. I use slow Kodachrome 64 whenever possible. Occasionally a faster Ektachrome gets loaded if most of the work is anticipated to be under heavy overcast or in deep shade.

b. Sanity check during a shoot:
Reflected light meters generally assume a scene averages to 18% gray, usually with some form of weighting. This is what humans perceive as half-way between black and white. If the meter varies by more than a half stop from the "sunny 16 rule" adjusted for overcast or shade, the reasons why the meter shows something different are sought. Many meters can be fooled by a very prominent specular highlight, deep shadow, or extreme imbalance between light and dark colors. At other times the meter finds a better average between highlight and shadow. Either way it triggers a closer evaluation of exposure settings. Sometimes it results in a reflected spot reading from an 18% gray card or an incident reading made with a hand-held meter to help decide.

c. Severe cold weather (10 F and below):
This isn't applicable to a completely electronic camera like the Canon EOS. I have three mechanical shutter cameras and use them in severe cold weather. The only electonics in them are the meters. In severe cold weather battery voltage eventually drops far enough that my electronic shutter cameras quit working. Under those conditions I use the mechanical ones. If the meter quits or becomes completely inaccurate because of voltage drop, I switch to the "sunny 16 rule" and keep shooting without a meter. Had to do this twice during January. There are ways to keep a camera warm, but a cold lens can fog with condensation as warm air crosses the dew point when warming the camera.

-- John

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March 22, 2001

I would class the 3.5-5.6 USM V Lens as "relatively slow" by 35mm format standards. It's not how fast it can focus, but the widest possible aperture.

In 35mm format I'm accustomed to manual focus systems with f/1.4 50mm lenses and many other prime focal lengths being f/2 or f/2.8. f/3.5 is only 1/3 stop faster than f/4, so I tend to think of an f/3.5 lens as I would an f/4 in this respect. Many auto-focus lenses are slower than manual focus lenses with the same focal length from older, manual focus systems. Both auto and manual focus zooms tend to be slower than prime lenses.

What is "fast" and "slow" are relative. In medium format (120 and 220 film) an f/2.8 lens is "fast" and an f/4 lens is not considered "slow," although it's not really a "fast" one either. The lenses for manual focus medium format systems are often two stops, sometimes one stop slower than their equivalents for 35mm format.

-- John

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March 22, 2001