I was wondering what the magnification power of my lenses was. So i googled it Nd found that a 50mm in 35mm format approximates what your eye sees and therefore 1x. So focal length divided by 50 gives approximate magnification power in 35mm. So what I am wondering then is with the 2x crop on our cameras, does that also apply to the magnification? For example a 50mm would be approx 2x magnification? Thanks! Matt
More or less. A 50mm on 2x crop gives the same view that a 100mm gave on 135 format film, which is to say 1/2 the width and 1/2 the height that a 50mm lens on 135 format film would give. A 25mm lens on 4/3 gives a similar angle-of-view to a 50mm lens on 135 format film. And so on. Generally magnification means something different though for photography - it has more to do with how big the reproduction of an object is when photographed at minimum focusing distance from a lens. If you photograph an object the same size as the camera's sensor from the minimum focus distance of the lens, and that image fills the frame, you've got 1:1 magnification. If that object fills only half the width and half the height of image, you've got 1:2 magnification. 1:1 magnification is considered 'true' macro. DH
The usual definition for the magnification of a lens refers to a reproduction ratio, being the ratio of the projected image on the sensor compared to the size of the object in real life. This is a lens characteristic, independent of the sensor used. However, since a m4/3 camera captures a smaller portion of the frame, and you would view the final image from a m4/3 camera at the same size an an image from a full-frame camera, it has an effective magnification of 2x.
For a lens that gives the same perspective as your vision, a lens with the focal length of the sensor/film diagonal is just about there. So, for 35mm film, it's actually about 43mm, but that's still only about 15% off. For our cameras, the sensor has a 22.5mm diagonal length. Therefore, lens zoomed to 225mm is about 10x.
So, if the picture is later enlarged and printed... to 10 times the original size anyway, is it wrong to think that in practical use, magnification means how much details you could get from the object ? The higher the magnification, the object is projected larger so the details can be made bigger than the smallest size the sensor/film could resolve (e.g: thing used to be smudged into 1 pixel now can be shown in 4 pixels with more details saved). CMIIW.
Yes, magnification of the image affects both sharpness (google "print size by camera format") and depth of field (google circle of confusion).
There are two types of magnification--angular magnification and linear magnification. Angular magnification is used for visual instruments and is what you are referring to. Calculating it is simple. Simply divide the focal length by the format diagonal. When you view a image/print at the distance equal to the dragon of the print, you will see the image at that angular magnification. (It is not quite that simple, but good enough for your purposes.) Linear magnification is image size vs. object size. This describes the reproduction ratio of a system. A macro lens working at 1X will project an image of a object 1cm long as 1cm on the image plane. Print size will change linear magnification and though you shoot something at 1X, you also need to calculate the further magnification the enlargement of the image goes through when printed. Viewing distance does not impact linear magnification. Magnification does not change sharpness nor depth of field of an uncropped image regardless of format--cropping does change those things, however. Viewing distance will also change those.
BTW, the diagonal of a 35mm frame is about 43mm and so the 50mm lens has an angular magnification of 1.16x (50/43=1.16). 35mm is about the only format that does not have a real normal lens.
There are a good number of 45mm lenses available for various 135 format systems. The gap between 45mm and 43.3mm proportionally less than that, between the 20mm Panasonic m4/3 and the 21.6mm diagonal of an m4/3 sensor and other lenses are even further off. DH
50mm is the normal focal length for 35mm film more by tradition than any mathematical consideration. It's what Oscar Barnack chose and we got stuck with it. Most classic 50mm lenses are a bit longer than their nominal focal length.
Ah, yes... this linear magnification. Usually I heard explanation about macro lens as lens with higher reproduction ratio (although there's also peoples explaining it as close focusing). But even if the object is projected same size to the sensor/film plane, the image will still need to be enlarged for viewing because 35mm film frame is tiny, and there's still issue about composing and framing the object. So, could it be that the practical thing about lens magnification is actually to help making the tiny details in objects big enough to be resolved by the sensor ? That's what I meant to ask
I am not sure what you are asking. Magnification is in relation to what you are photographing--a landscape has little magnification, a microscope has great magnification. Naturally, in each case, certain elements have to be resolved in order for the image to appear detailed and sharp. The first step is to have the detail you need appear in the original data.
While it doesn't show the actual magnification, this article by Thom Hogan Lens Angle of View | byThom sans Mirror | Thom Hogan has a really good run down of angle of view compared between different sensors.