magification : LUSENET : Large format photography : One Thread

if i had a 300mm lens on a SLR ,what would the power equlant power be . example 8x 16x

-- robert koch (, November 11, 1999


Equivalent to what? Compared to a "normal" 50mm lense in 35mm, a 300mm lense magnifies the image 6x - 300/50.

A 300mm lense is a 300mm lense, irrespective of whether it is designed for large, medium or 35 mm format. By this I mean that any lense of a given focal length will give the same size of image on the film. However, as the film size on which the image is being projected changes (say from 35mm, to 6x9cm, to 4x5 inches), the apparent field of view changes. Consequently, if you're photographing a mountain, a 300mm lense on a 35mm slr may view only the summit (say), but in 4x5 format, may view the whole mountain. However, if you compare the two images, the size of the summit should be the same on each piece of film.

Distinct from this is the covering power of the lense, i.e. over how wide a field the image is projected. Any 4x5 lense would cover 35mm, but it is extremely doubtful that the converse is true.

-- fw (, November 11, 1999.

if your answer is what is the focal length equivalent for 4x5 of a 300mm lens for a standard format 35mm SLR, the answer is approx 900mm.

-- Ellis Vener (, November 12, 1999.

This is the Large Format forum (film sizes 5x4 inches and upwards, roughly). So Robert, are you talking about LF SLRs? Whether a camera is an SLR probably makes no difference to your question.

Perhaps you are referring to 35mm SLRs. I'm afraid I don't understand your question. Binoculars and telescopes do have powers, because they magnify an image to the naked eye. Cameras and their lenses only this incidentally, their real purpose is to put an image on film, so they don't have 'powers'.

However, some 35mm cameras when used with a 50mm lens present an image to the eye at a magnification somewhere near 1, in which case a 300mm lens will magnify about 6X.

-- Alan Gibson (, November 12, 1999.

Mr. Gibson is correct, lenses don't really have "powers".

Magnification is the ratio of the size of the original object to the size of the image. So if you photograph a 2 meter tall object and it comes out 2 cm tall on your film, your magnification is 1:100 (you'll have to excuse me if I'm getting these ratios backward, but you'll probably get the idea) or .01X When you talk about the "power equivalent" of a camera lens, that's because it has been decreed that on 4x5, that 150mm is a normal lens, therefore that is a 1X lens even though you may be photographing an object at a magnification of .01X.

Now it just so happens if you put a 300mm lens on your 4x5 camera and take another picture of that 2 meter object, it will be imaged as 4cm on the film, and your magnification is now .02X. But since this magnification is twice what you get with a "normal" lens, you could say that your image is 2X normal.

So, if you stand at point X and take a photo of the same thing with a 50mm lens on your 35mm camera and a 150mm lens on a 4x5 camera. The object is imaged 3 times larger on the 4x5 film. If you put a 300mm lens on both cameras, the object is resolved the same size on both pieces of film. But in the 35mm case, it's 6 times larger than with the 50mm lens, and in the 4x5 case, it's 2 times larger than with the 150mm lens.

-- mike rosenlof (, November 13, 1999.

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