Relative mag factors made 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 <gasp> think! 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 free - go forth and rejoice! k
