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01-17-2014, 05:25 PM   #16
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QuoteOriginally posted by Wired Quote
This means that wide angle lenses which are known for distorting things and make faces appear wider will still do that.
I'm not following. With the size of the face kept constant in the shot, my wide angle lenses make faces look narrower than a normal lens, not wider. And when you stick that full-frame wide angle lens on an APS-C camera, the distortion does get reduced, since the sensor now captures a center-cropped section of the full frame. More importantly, though, the perspective of that formerly wide-angle 35mm is now such that it approximates that of the naked eye at the same distance, i.e. it becomes a 'normal lens'.

Last edited by Ikarus; 01-17-2014 at 05:40 PM.
01-17-2014, 05:43 PM   #17
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My favourite portrait lens would be my Sigma 70 macro, 2.8. And I would have been using 80-100mm on film.
Sigma 70mm F2.8 EX DG Macro Lens Reviews - Sigma Lenses - Pentax Lens Review Database
SIGMA 70mm F2.8 EX DG Macro - Macro Lenses -

01-17-2014, 07:33 PM   #18
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Distortion is two types: 1. one the closer stuff is larger with wider angle lens (so nose is too large), but also 2. as you go to the side of the lens the distortion changes shapes--circles become distorted ovals--or narrower. But the type 1. is because you move closer w/ wide angle lens. If not closer (same distance) then no change, no matter what the FL.
01-17-2014, 07:35 PM   #19

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QuoteOriginally posted by Wired:
Now here is where it gets annoying and all strange... one would be lead to believe that a 50mm lens magically becomes a 75mm lens when you slap it onto a Pentax DSLR. Sure the field of view becomes similar, but its not that simple. A 50mm lens will always render like a 50mm lens, no matter what camera it's mounted to. This means that wide angle lenses which are known for distorting things and make faces appear wider will still do that. a 50mm lens is heralded as the standard lens because it renders closer to the human eye than other lenses. On a film body this would also give you a field of view pretty close to your own...but on an APS-C it "zooms in". A lens in the 60-90 range would in term make faces seem thinner.
I don't understand the point about the 50mm lens not "becoming" a 75mm lens. I don't understand the effective difference.

Getting back to the original question, it seems like a very small percentage of professional portraits are made at larger apertures than about f2.8. Obviously there are exceptions, but for a class I'm sure the existing lenses would be more than adequate.

Last edited by tibbitts; 01-17-2014 at 07:42 PM.
01-17-2014, 08:46 PM   #20
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If you don't change distances the 50mm lens on a (cropped) dslr or a FF will have the same view--as regards relative size of things closer or further away, but the dslr field of view is less--because it's 2/3 the size of film. But this means you don't use the 50mm lens to take the picture from the same distance, if you want the same field of view--and thus the near-far relationships change. On a dslr you are further away, so the lens is actually like a longer FL--as regards the near-far relationships. (Actually from the same distance all lenses have the same near-far relationship but this may be confusing.)
01-18-2014, 04:37 PM   #21
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Perspective distortion is a function of distance to subject. All focal lengths will produce the same amount of perspective distortion at the same distance, its just that the size of the subject in the image will be much smaller for a wide angle than telephoto. Because people frame an image the same no matter the focal length, the use of wide angles will cause you to take a photo too close to a subject and distort their features.

An 85mm lens on film/FF is ideal for framing a head and shoulders portrait at the ideal distance from the subject for minimal facial distortion. On an APS-C sensor camera a 55mm lens will place you at the same framing distance. The only difference is that the 85mm will have a narrower depth of field than a 55mm at the same aperture.

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