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View Full Version : (real world) camera question.. Distortion



hrgiger
05-05-2007, 11:47 AM
I must confess that I know nothing about photography but I know that some of you do so hopefully you can help me.
I want to take some pictures of my girlfriend so that I can use as backdrops in modeler. The problem I"m getting is there seems to be a fair amount of distortion. Sort of like when you get close to a convex mirror and reality seems to bend a bit. How do I take a straight on photo with the least amount of distortion possible? Do I need to take it further back from the subject (i.e. The provider of thy nookie)

The camera I'm using is a Canon EOS Digital Rebel. The lens says EFS 18-55mm. Just so you know, I have no idea what any of that means, as I said, I have no interest in photography.

walfridson
05-05-2007, 11:52 AM
Use max amount of zoom and move backwards.

Otherwise most imageapps have some sort of undistort filters.

Limbus
05-05-2007, 12:39 PM
The Digital Rebel has a crop factor (zoom multiplier) of roughly 1.6, which will give approximately 88 mm in the classic sense.


No it won´t. It will give a 55mm lens picture cropped to a viewing angle of a 88mm lens. The crop factor does not change the focal lenght.


Magnification factor

The crop factor is sometimes referred to as "magnification factor." This usage commonly derives from the telephoto effect, in which lenses of a given focal length seem to produce greater magnification on crop-factor cameras than they do on full-frame cameras. It should be noted that the lens casts the same image no matter what camera it is attached to, and therefore produces the same magnification on all cameras. It is only because the image sensor is smaller in many DSLRs that a narrower FOV is achieved. The end result is that while the lens produces the same magnification it always did, the image produced on small-sensor DSLRs will be enlarged more to produce output (print or screen) that matches the output of a longer focal length lens on a full-frame camera. That is, the magnification as usually defined, from subject to focal plane, is unchanged, but the system magnification from subject to print is increased.
http://en.wikipedia.org/wiki/Crop_factor

Nonetheless setting the lens to 55mm will give you nice undistorted images of you girlfreind than you then can post here :jam:

;-) Florian

Limbus
05-05-2007, 01:38 PM
Close enough but no banana, I guess. I forgot that minor technicality.

Thank you for correcting my blasphemous error :)

I shall forgive you ;-)

I just think its important to understand it correctly because it makes it much easyer when you dig more into the material and start to think about the relation between sensor size, aperture, focal length and DOf etc...

Florian