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Here's
a quick reference chart to let you compare focal lengths from one camera
format to another. Just find the degree of coverage for any lens in one
picture format, then locate the lens with the same degree of coverage
for the other format.
Let's
say you like the perspective you get with a 135mm lens on your 35mm
camera, but you're thinking of moving up the line to a 6x4.5 camera.
What focal length will you need on the 6x4.5 to give you the same
results? Go down the left-hand column until you locate the 135mm line.
Follow that line across to the 35mm format and note the angle of
coverage: 18 degrees. That's the angle you'll want for your 6x4.5
camera. Now go down the 6x4.5 column until you come to the focal-length
lens with the same or nearly the same angle of coverage. You're in luck;
the 250mm focal length covers the same angle on 6x4.5 as the 135mm lens
on your 35mm camera.
Since not all formats could be listed you may need to use a close match.
For instance, what lens on a 35mm camera will give you the same
perspective as a 300mm lens on your 4x5 camera? The 4x5 column shows the
lens covers 30 degrees. Looking at the 35mm camera column, you'll find
that a 75mm lens covers 32 degrees and an 85mm lens 28 degrees. So a
300mm lens on a 4x5 camera is right in the middle, equivalent to an 80mm
lens on a 35mm camera.
All
degrees represent measurements across the diagonal of the camera format,
which is the "official" unofficial means of international
measurement. For the Advanced
Photo
System, the HDTV format is the standard. It produces 4x7-inch prints,
the size most APS users seem to prefer. The diagonal for HDTV by the way
is 35mm, which ought to confuse a lot of people.
camera
length; conversely, multiply the 35mm camera focal length by .8 to get
the APS equivalent focal length.
A quick
way to compare 35mm and APS is to multiply the APS focal length by 1.25
to get the equivalent 35mm
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