Relative mag factors made simple:
In the OLD day, photographers learned photography. they learned how cameras worked, how films, lenses and optics worked. they learnt about light, they learned some chemistry, they learned how to be creative and make stuff out of wire, string, twigs and small children when the need arose.. in short they were well versed in many technical things and were pretty lateral thinkers.
As time went on things got dumbed down in the photo industry - a degree of automation was introduced into point and shoot cameras, and in time these same little knick-knacks found their way onto more complex cameras. Eventually the manufacturers started producing cameras with all sorts of automation, painted them black and called them 'professional' cameras and pro's started using them.
Since then, photographers seem to have adopted this new stuff and rejected the studies in the old ways, and as you'd expect in time, eventually a lot of what was known was lost.
Consider lens focal lengths. These days digital camera sensors come in all shapes and sizes, and someone buying a camera needs to know what the field of view (old technical term) for each lens was - of course the old tech types could work this out in a mere moment, and tell you straight away what focal length they needed for a given shoot for any particular format - it was an a squared plus b squared sort of thing..
Anyhoo, the modern shooter with their modern zooms don't know about things like 8x10's, 1/2 frames, 617's and the like, and focal lengths confuse them - so I've prepared a primer to make things simple.
Lets look at a canon 300D, a camera with a sensor size of 23x15mm. We
don't need to really know the size of the sensor any more because the magic
of magnification ratios renders the need for understanding what focal
length actually means and it's relationship to format redundant. A
comprehension of formulas such as a^2 +b^2 = c^2 is no longer important,
and no longer is that old fuddy duddy stuff about light from 'infinity'
focussing somewhere or other.
All you need to know now is the magnification ratio of any lens fitted to a
300D relative to a 35mm lens is 1.8 - magic!
This means we get longer lenses on a 300D than on a 35mm camera.. another
way of looking at it is to say the magnification ratio is 11.6 relative to
8x10, which means a 50mm lens on an 300D is an equivalent to a 580mm lens
on an 8x10, or a 300mm lens equals a 3,480mm lens - how cool!
So.. 35mm has a mag factor of 6.4 relative to an 8x10, so a 50mm lens on a
35mm is equal to a 320mm lens on an 8x10, or a 1000mm lens = 6,400mm ! To
put this another way, a 100mm lens on a 35mm camera has a mag factor of 3.2
(8x10) but that's based on an 'actual' focal length, the relative mag
factor remains 6.4 for any given lens. Looking at a 6x6, THIS format has a
mag factor of 3.8 compared to an 8x10, or to compare the other way, a 300D
has a mag factor of 3 relative to a 6x6 (with a 'normal' focal length of
84mm) 645 on the other hand provides the 300D with a relative mag factor
of 2.7. on a 645, a lens has a relative mag factor of 4.26 compared to an
8x10, so instead of getting a boring old 180mm portrait lens on 645 like we
used to in the old days, in these enlightened modern times we could think
of our 180mm as being a 767mm lens!
Yay! We now have a really impressive lens where before it was only
moderately so-so, thanks to the magic of 'magnification ratios'.
Eeducation courses can now eliminate the old fashioned rubbish and spend
more time teaching PhotoShop�
Now all we need to do is remember all the relative magnification ratios as
they are told to us by manufacturers knowing that they are being honest
with their format OR in the case of the caring camera maker who does the
conversion for us and marks their 16 - 48mm lens as a 35-105mm lens, we
don't need to think at all! Of course this isn't much use if you pop it on
another camera so maybe they could make interchangeable lens rings with a
guide based on models so we could fit the appropriate focal length ring to
our lens whenever we change it from Nikanon� to a differing Nikanon� it'd
make things a lot simpler! For those folk who try to experiment (which
should be discouraged) and use non propriety lenses on differing cameras
like say fitting a 50mm lens (or call it a 90mm on a 300D) to an 8x10 for
macro work, there should be NO conversion focal length rings made available
and a database of such individuals should be established to allow
re-education to take place.
It's fantastic how in this technamological world all the thinking is being
done for us and all we need do is buy when we're told to, chant the figures
we're given and it all becomes so simple.. much better than having to
actually look up a formula and
So now we all know that a 50mm lens is actually ANY focal length, 7.8mm,
90mm or whatever and the old constraints that held back our creativity have
been blown away like old dust that dared settled on our new ipod� - we are
now completely free - go forth and rejoice!
5:13 p.m. - 2005-09-26
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