BetterPhoto Q&A
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Photography Question 
Dean Boyer

Film speed

what speed of fim would you use in bright sunlight? and whats the difference between
print film and slide film in speed

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9/30/2003 2:29:17 PM

John A. Lind
BetterPhoto Member Since: 9/27/2001
Film speed range for photographs in bright, direct sunlight: ISO 25 to ISO 160.

"Slide" film is also called "transparency" and "print" film is also called "negative." There is no relationship between film speed and film type (transparency versus negative). Each film has its own rated speed. The difference between negative and transparency is the film developing chemistry used (and the end result being a transparency or negative).

-- John

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9/30/2003 7:05:18 PM

Tony Sweet
Tony's Photo Courses:
2-Week Short Course: A Quick Start to Adding More 'Pop' to Your Images
  The quick answer, Dean, is ISO100 or ISO200. That way you are able to hand hold your camera at f/22 to get the sharpest images possible. Normally, f/22 will give you a shutter speed too long to hand hold your camera without getting blur, but the higher ISO will give you a faster shutter speed that will help elminate camera shake.

Speed is not an issue between print and slide film. Slide film is better for publication and for projection on a slide projector to show large groups or for presentations.

Hope this helps!

Tony Sweet

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10/1/2003 2:24:56 AM

John A. Lind
BetterPhoto Member Since: 9/27/2001
  I disagree with Tony about "sharpest images possible" using a lens aperture of f/22! With most 35mm film format lenses, a lens aperture that narrow is well into diffraction limiting that degrades resolving power of the lens. It will produce the greatest depth of field, but the portion of the image at the critical focus distance will not be as sharp as it could be at a wider aperture.

When light passes through a small hole it diffracts (spreads). The smaller the hole, the worse the effect. This is why most 35mm format lenses have a "sweet spot" of highest resolution between about f/5.6 and f/11. It's also why most lenses shorter than about 90mm don't stop down farther than f/16. Longer lenses often stop down more as the absolute diameters of the lens exit pupils for the higher f-stop numbers are larger. The diffraction effect is driven by absolute aperture diameter (at exit pupil) and not by what the f-stop number for that diameter happens to be.

Want the sharpest possible image? Use an aperture of f/8 unless there is a compelling need for more depth of field.

-- John

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10/2/2003 8:53:24 PM

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