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Thread: Portrait perspective issues investigated

  1. #21
    J. Austin Powers appletree's Avatar
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    Re: Portrait perspective issues investigated

    Now I got it! I think using the example of print messed me up, because at first I was thinking actual print from a negative. Enlarging to an 8x10 or 16x20, etc.

    from wikipedia:
    "Note that linear perspective changes are caused by distance, not by the lens per se – two shots of the same scene from the same distance will exhibit identical perspective geometry, regardless of lens used. However, since wide-angle lenses have a wider field of view, they are generally used from closer, while telephoto lenses have a narrower field of view and are generally used from farther away. For example, if standing at a distance so that a normal lens captures someone's face, a shot with a wide-angle lens or telephoto lens from the same distance will have exactly the same linear perspective geometry on the face, though the wide-angle lens may fit the entire body into the shot, while the telephoto lens captures only the nose. However, crops of these three images with the same coverage will yield the same perspective distortion – the nose will look the same in all three. Conversely, if all three lenses are used from distances such that the face fills the field, the wide-angle will be used from closer, making the nose larger compared to the rest of the photo, and the telephoto will be used from farther, making the nose smaller compared to the rest of the photo."

  2. #22

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    Re: Portrait perspective issues investigated

    You can get in close with a normal lens for a portrait. You just have to be careful with the pose to avoid distortion. A longer lens makes it a lot easier. The longer the lens the more you flatten the subject. What focal length looks best? Well, you learn from experience what you like. It really is a personal decision which is why I recommended to the OP to try his 210mm and if he wasn't happy then try something longer.

  3. #23

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    Re: Portrait perspective issues investigated

    If you want the print (yes the 8x10 or whatever) to have normal perspective the print viewing angle needs to match the taking angle.
    You can't depend on your eyes when your imagination is out of focus. ~ Mark Twain

  4. #24
    Dan Quan's Avatar
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    Re: Portrait perspective issues investigated

    Quote Originally Posted by Mark Barendt View Post
    Morning Ulophot,

    The disparity between the geometry of the shot and the geometry of the print view, is what introduces the bulging or flattening look/perspective to any photo. The rules of the universe don't care about the limits of our darkrooms or cameras or how big our studios are.

    If the eye is in the right place (has the same view the camera did) the print will look normal regardless of what the head vs foot measurements are.

    If the foot looks too large when viewing the print I'm going to guess that the viewing distance to the print is simply too long, get your nose closer or print bigger and see if it looks more normal. If that works then to fix the problem you may need to move the subject further from the camera and crop or ...
    I have never heard this but it makes sense in my ignorance. Can you explain it again more concisely and possibly more simply please?
    “Life is short. Break the rules. Forgive quickly. Kiss slowly. Love truly. Laugh uncontrollably and never regret anything that made you smile!”
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  5. #25

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    Re: Portrait perspective issues investigated

    Quote Originally Posted by Dan Quan View Post
    I have never heard this but it makes sense in my ignorance. Can you explain it again more concisely and possibly more simply please?
    So I'm going to blow up the scale here little bit to see if I can clarify the idea.

    Take any camera & lens and take a photo. No cropping. Blow the photo up really big, say printed on the garage door of a two car garage.

    Set up your camera in front of the garage door the move the camera forward and back until you have the print filling the viewfinder edge to edge.

    When you're standing at the camera the print will look normal.

    If you go straight forward closer to the print, the subject matter in front of you, will start to look flattened.

    Back up behind the camera ways and the print will start to distort and look "wide angle".

    This technically works for any lens. In a practical sense it is the most visible when a true wide-angle lens has been used.

    In our example a camera with a wide angle lens might end up 20 feet from the garage door. At that point it's easy to get in front of or behind the camera.

    When a long narrow angle Lens has been used to take a photo it is tough to get far enough back away from the print to see the effect change much, it always looks flattened.

    Think about shooting a 300 mm lens on a 35mm camera and printing on the garage door, now use that same camera and lens and backup until you get that print framed perfectly in the viewfinder. The camera might be back a hundred feet or more from the print.
    You can't depend on your eyes when your imagination is out of focus. ~ Mark Twain

  6. #26
    Sheldon N's Avatar
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    Re: Portrait perspective issues investigated

    Quote Originally Posted by mdarnton View Post
    Shooting LF is much different from 35mm. With 8x10 portraits you are approaching what would be macro ratios in 35mm, but at greater distances, still with the very large extensions of macro photography*, resulting in a lens of effectively longer focal length. The way to understand how this works is to dig in and do it.

    *(an 8x10 head+ shot might be shot at 1:2, with a 14" lens being used at 21" from the film, where the same shot on 35mm is done with a negligible focus extension, at a very different reproduction ratio.)
    +1

    This is a significant issue for shooting close up portraits, even with 4x5 but especially with 8x10. When you focus close, you extend the bellows. When your bellows extend, the field of view of your lens narrows. By the time you get to 1:1 magnification (ie. 4x5' or 8x10" subject size at plane of focus for 4x5 or 8x10 film) you have doubled your bellows extension and cut your field of view in half. On 4x5 with a 210mm lens that would mean that you would have 420mm of bellows extension and would have an effective field of view (effective focal length) of 420mm. It's obviously a sliding scale for any magnification between infinity and 1:1 macro. Here's a quick rule of thumb to help estimate the effect.

    Your "effective" focal length is roughly the same as the amount of bellow extension used.

  7. #27

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    Re: Portrait perspective issues investigated

    Quote Originally Posted by Sheldon N View Post
    Your "effective" focal length is roughly the same as the amount of bellow extension used.
    Yes.

    The focal length marked on a lens is only right when focused at infinity.

    Part of the struggle in explaining "my" concept above is this variation in focal length to focus. When framing the print on the garage door in my example I have to ignore focus. The camera needs to be focussed like it was focussed when shot, not focussed on the garage door.
    You can't depend on your eyes when your imagination is out of focus. ~ Mark Twain

  8. #28

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    Re: Portrait perspective issues investigated

    Funny, I had a dream about this last night. It's a clever argument and often repeated as the justification for using shorter lenses in ULF, but, I wondered if the laws of optics of a 420 mm lens are the same as the laws of optics of an "effective 420mm lens" i.e. a close focussed 210mm lens. I should like to see some evidence of this, before I necessarily buy into this oft repeated statement. Especially, since, as the field of view is cut off, the lens must move closer to the subject to fill the frame (as in close up portraits)

    Quote Originally Posted by Sheldon N View Post
    +1

    This is a significant issue for shooting close up portraits, even with 4x5 but especially with 8x10. When you focus close, you extend the bellows. When your bellows extend, the field of view of your lens narrows. By the time you get to 1:1 magnification (ie. 4x5' or 8x10" subject size at plane of focus for 4x5 or 8x10 film) you have doubled your bellows extension and cut your field of view in half. On 4x5 with a 210mm lens that would mean that you would have 420mm of bellows extension and would have an effective field of view (effective focal length) of 420mm. It's obviously a sliding scale for any magnification between infinity and 1:1 macro. Here's a quick rule of thumb to help estimate the effect.

    Your "effective" focal length is roughly the same as the amount of bellow extension used.

  9. #29

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    Re: Portrait perspective issues investigated

    Quote Originally Posted by cowanw View Post
    Especially, since, as the field of view is cut off, the lens must move closer to the subject to fill the frame (as in close up portraits)
    This sentence doesn't make sense.

    The angle of view for specific lens remains constant, as the lens moves farther from the film the projection at the film gets larger, more coverage. This is the reason that coverage is also measured normally at infinity Focus.

    If a 420 and 210 lens both had the same angle of view, then both would cover the same area when focused at the same bellows draw, what would not be the same is the focus.

    What Sheldon was getting at though is the limitation of the camera if all I can hold is 4 x 5 film moving from 210 to 420 change is the angle of view that the camera can see, it does not change the optics of the lens but it does change where the plain of sharp focus falls.
    You can't depend on your eyes when your imagination is out of focus. ~ Mark Twain

  10. #30

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    Re: Portrait perspective issues investigated

    Why so much talking? This is really easy to demonstrate:
    A 12" lens is a bit shorter than 8x10 diagonal, which is about 12.5". 35mm diagonal is about 42mm, so a 42mm lens would be a hair longer equivalent on 35mm film to the 12" on 8x10, but it's close enough. If the two function equally at portrait distances, they should cover the same field when the lenses are at the same distance from the subject, right?

    I just set up my 8x10 with a 12" lens pointed at my book case at portrait distance so that the vertical field of view was two shelves---30 inches. The total bellows extention is 15.5 inches, which is conveniently close to equivalent to 50mm on 35- approximately diagonal plus 20%, in both cases. The extension of the 50mm at this distance is, of course, negligible. If the case under discussion is true--that it's not the lens but the extension--then the 50mm (which is a long lens on 35mm by the normal rules) at the same distance (same lens to subject distance) should be cover the same as the 12".

    And it does. A 35mm lens, which isn't too far from being a 12" equivalent, is wildly wider--another shelf and then some more. That makes a 12" on 8x10 about equal to 50mm on 35mm film. I suspect that with longer lenses on 8x10 the situation becomes even more in favor of these lenses acting like their extension, not their focal length.

    The important point is that perspective = field of view compared with eye to subject distance. All the rest is extraneous.

    You can do this at home, if you have a camera. :-) In fact, someone who's more fussy than I am should do it and report back.
    Thanks, but I'd rather just watch:
    Large format: http://flickr.com/michaeldarnton
    Mostly 35mm: http://flickr.com/mdarnton
    You want digital, color, etc?: http://www.flickr.com/photos/stradofear

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