Magnification? What's that?

Ok, I feel quite stupid asking this question, but then again it keeps bugging me so I hope someone can answer this for me without laughing:

Every now and then we read posts here of SLR users making fun of P&S shooters asking "so, what kind of magnification do you get with this thing?". The usual response would be something like "well, 1" in the case of a prime.

I looked at the specs of a few Canon lenses recently and noticed that they give magnification ratios. For example the 300 f/4 is 1:4.2, the 400 f/5.6 is 1:8.3 and the 100-400 is 1:5.

So are the P&S shooters really asking silly questions or am I comparing apples and oranges? Are the magnification ratios something unrelated and how are these numbers calculated? Why is there such a difference between the 400 and the 100-400?

The numbers you just mentioned is probably not what you were after. They are about close focus and macro capabilities. A 50mm has magnification of 1x, a 100mm is 2x, a 400mm would be 8x. Then you can compare what you'll see through a lens to any pair of binoculars.

Often, P&S cameras will express zoom ratio in terms of ?X, such as 3X, 7X, etc. based on the focal length at the long end of the range vs the FL at the short end. Manufacturers might do this so as to not confuse their potential consumers with actual lens focal lengths and the effect of the sensor size in determining the field of view that can be achieved at those focal lengths. If I remember the thread correctly that you refer to, the poster had a long focal length prime mounted on his DSLR and was asked by the unknowing questioner something to the effect of how many times (X) magnification/zoom he could achieve. Since he was shooting with a prime, the true answer was "1X". The "magnification" specified for lenses (1:4.2, for example) relates to the size of the image that is possible in close up photography compared to the actual size of the subject being photographed.

dazzlebea wrote in post #2116991
Are the magnification ratios something unrelated and how are these numbers calculated?

They are in relation to "life-size". A 100mm f/2.8 macro lens gives 1:1 magnification at the minimum focus distance. This means things are life size. Something that is 10mm long will be 10mm long.


On the other lenses, that ratio decreases, as they can't focus as close as the macro lens can.

Because, the minimum focusing distance on the 400 5.6L is 11'. The mfd on the 100-400 is 5.9'.

Ronald S. Jr. wrote in post #2117410
They are in relation to "life-size". A 100mm f/2.8 macro lens gives 1:1 magnification at the minimum focus distance. This means things are life size. Something that is 10mm long will be 10mm long.

On the other lenses, that ratio decreases, as they can't focus as close as the macro lens can.

Because, the minimum focusing distance on the 400 5.6L is 11'. The mfd on the 100-400 is 5.9'.

These numbers can throw people off... I know that when I first got into photography it confused the hell out of me. I'll try to add the bits that are missing that helped me understand the whole macro magnification bit.

As Ron said, 1:1 means lifesize at minimum focus. What got me was how a 1:1 magnification (lifesize) photo of a fly's head can be so huge on a print with such detail... that certainly isn't lifesize...lol. Well, the size actually refers to the size of the focused subject on a frame of film. Since the 100mm F/2.8 macro lens is designed for EF mount or film/FF digital, that means that for something to fill the frame at 1:1 magnification at minimum focus, it would have to be 35.8mm x 23.9mm in size.... of course this also means if you printed this at 4x6... the object would be 4" x 6", 8x10 would be 8"x10", and so on. So let's say our fly is about 18mm long... that would mean he'd take up about half of the left to right size of the frame. Hopefully this makes a little sense now.

Thank you all so very much, I've got it I suspected that P&S magnification was not the same as DSLR magnification but somehow my mind wasn't able to wrap itself around these concepts. Now I better move carefully or it will all get jumbled up again