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At the bottom of the poll screen is a small "advanced options" box where you can allow multiple selections. Unfortunately, once a poll has one response as originally set up, I cannot go back and edit the poll to accept multiples.What do you think affects perspective?
I had hoped that you could have answered each question, not just selected an option, but I cannot see an option to delete the poll, and do not know how to create a multiple-question poll?
The options are limited to 100 characters, and, of course, tilt or swing would both affect the perpendicular image distance... the distance measured perpendicular to the image plane to the subject... I do not know if Wikipedia of Merklinger have a name for it.Q3 ... front tilt or rear tilt? Why tilt and not swing?
Thanks Jack.At the bottom of the poll screen is a small "advanced options" box where you can allow multiple selections. Unfortunately, once a poll has one response as originally set up, I cannot go back and edit the poll to accept multiples.
You have to restart a new thread with all the questions you want, and check the "allow multiple responses" box near the bottom of the poll creation page. I cannot edit the reply format, other than to delete or add questions, once a poll has been replied to.Thanks Jack.
I set up the poll without an end date - is it possible for you or I to end the poll so I could start again with a multiple question?
Focal length does not affect perspective if you keep the object distance the same. This is irrelevant if you adjust the view point (subject distance) to get the same reproduction ratio (object image size).Today the popular myth is to say it is object distance only--where in the past folks recognized that lens choice could change the sense of space in an image (this is where viewing distance comes in). The "object distance only" view does not align to the the theories in linear perspective nor our perception of images. If perspective is simply object distance, how can we see, and see clearly, that an image has been taken with a wide angle or telephoto lens?
I never said focal length changes perspective.Focal length does not affect perspective if you keep the object distance the same. This is irrelevant if you adjust the view point (subject distance) to get the same reproduction ratio (object image size).
What were you trying to say or imply with:I never said focal length changes perspective.
The pictures in your link clearly show the effect on perspective of changing the viewpoint and changing the scaling in printing or post-production to keep the subject image of the girl the same size in the finished prints... but you can achieve the same effect by scaling (to keep the image of the girl the same size) by varying the focal length as you move the camera... and get a higher res finnished picture by not having to crop and scale up. ¿Is this complicated?If perspective is simply object distance, how can we see, and see clearly, that an image has been taken with a wide angle or telephoto lens?
And did you read the text explaining about viewing distance?What were you trying to say or imply with:
The pictures in your link clearly show the effect on perspective of changing the viewpoint and changing the scaling in printing or post-production to keep the subject image of the girl the same size in the finished prints... but you can achieve the same effect by scaling (to keep the image of the girl the same size) by varying the focal length as you move the camera... and get a higher res finnished picture by not having to crop and scale up. ¿Is this complicated?
I do appreciate that this is true... all I am saying is that using a lens of a different focal length allows us to change the viewing distance without changing the subject image size... it is really not very complicated.And did you read the text explaining about viewing distance?
It is viewing distance that changes the apparent perspective. It is viewing distance that that allows us to perceive differences in the talking position and, by extension, the angle of view.
No disagreement from me. I had that in my first post.I do appreciate that this is true... all I am saying is that using a lens of a different focal length allows us to change the viewing distance without changing the subject image size... it is really not very complicated.
Tim,An interesting point I discovered recently is that front tilt affects perspective as well as rear tilt. It's suggested that rear tilt causes looming and front tilt does not. However, the effect of looming is caused by tilt - the part of the sensor that is focused closer is magnified, an integral effect of having a lens further away from the sensor (i.e. focused closer). However, the effect of tilt on the front sensor is minimised by the associated perspective change caused by the fact that the image projected on the sensor comes from closer to the edge of the image circle.
Answer:
Two things affect perspective: Lens position and sensor plane angle, PERIOD -- ~~~ If you alter the lens position in any fashion, moving the camera or adding rise or shift via the front standard, you've altered the lens position and hence altered perspective. ~~~ In some systems, lens tilts or swings actually alter the lens position and hence can also affect perspective. However, if the lens standard tilts and swings are true axial movements around the optical center of the lens (exit pupil), perspective will not be altered.
Yes but you will also 'distort' even if they *are* axial with the lens center. Adding tilt means that one end of the sensor is further away from the lens plane than the other end of the sensor. When you move the sensor further away from the lens plane, light diverges and you end up with the image being 'enlarged' (hence why your image circle gets bigger when focussed closer).Tim,
I indicated this very thing above and if your lens tilts altered perspective they were obviously not axial with the lens center (lens exit pupil):
Tilting/swing the lens around the rear nodal point does not change the distance from the lens to the sensor. It will change the plane of focus. Magnification is simply proportional to lens to sensor distance and tilts and swings properly set on the lens standard does not change that. If you are changing perspective with your tilt/swing, then you are not rotating the lens around the rear nodal point. The problem will be with your cameraYes but you will also 'distort' even if they *are* axial with the lens center. Adding tilt means that one end of the sensor is further away from the lens plane than the other end of the sensor. When you move the sensor further away from the lens plane, light diverges and you end up with the image being 'enlarged' (hence why your image circle gets bigger when focussed closer).
Hence if one side of the image is magnified more than the other, you have a distortion. The effect of this distortion is reduced by applying changes to the front standard because tilt on the front standard is the same as tilt+rise/fall on the rear standard.
Next time I get out with a camera I'll take a couple of pictures to demonstrate this.
Tim