# lens conversion factor



## jimaroo (Jun 14, 2006)

hey i cant find this in any other thread.

if you have the rebel xt and are using a film lens thats 28-80 don't you have to multiply it by something to get the actual zoom that its going to be for the digital?


i heard its some thing like, multiplying it by 1.7 i don't really know. just wondering


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## bigfatbadger (Jun 14, 2006)

1.6 I think so your 28-80 becomes a 45-128, except with less picture area


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## jimaroo (Jun 14, 2006)

oh ok thanks


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## Big Mike (Jun 14, 2006)

It does not actually change the (focal length) magnification of the lens.  Basically, with a Rebel XT (or camera with similar sized sensor) you are only seeing the centre part of the image that is projected by the lens....which was designed for 35mm film.

So your 28-80mm lens when on a Rebel XT will have the same * Field of View* as a 45-128mm lens would on a 35mm SLR (or full frame digital).

This is really only a factor if you know what the FOV is on a 35mm SLR...because the same lens will be different on a Rebel XT.  If you are not used to using a 35mm SLR then don't worry about the crop factor at all....it's just a comparison number for people who are used to film cameras.


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## markc (Jun 14, 2006)

Big Mike said:
			
		

> If you are not used to using a 35mm SLR then don't worry about the crop factor at all....it's just a comparison number for people who are used to film cameras.



I agree. You have to do the same when switching to medium format, 4x5, or 8x10. But if you only shoot 4x5, it doesn't matter what the 35mm equivalent is.


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