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04-03-2008, 11:05 AM   #46
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QuoteOriginally posted by moxfyre Quote
Also, taking a flower at 1:1 will NOT give you the same picture regardless of focal length!! If you do it with a 300mm macro lens, you'll have to put the camera about 5 feet away. If you do it with a 50mm macro lens, you'll have to put it about 1 foot away. The perspective will be completely different... the flower will look "flattened" with the telephoto lens, whereas it will look more 3D with the 50mm lens.

Oppss. Now the perspective comes back to haunt me .

I probably need to reread all of the definitions before I talk again .

However, when I reread the whole thread, what I (and possibly thepirate) refer as "reach" is just simply "magnification" by your definition. Since your definition said that magnification is defined by FL and CTS distance, that would explain the beginning of discussion about FF vs. crop sensor.

So if you keep the same FL and CTS distance, then the magnification stays the same when you move from FF to crop sensor. Of course, it also comes to the discussion of either the lens or sensor as the limiting factor.

I think you now clearly understand what I meant by "reach" . Definitely not a conventional textbook definition.

04-03-2008, 11:10 AM   #47
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QuoteOriginally posted by aegisphan Quote
So if you keep the same FL and CTS distance, then the magnification stays the same when you move from FF to crop sensor. Of course, it also comes to the discussion of either the lens or sensor as the limiting factor.
Bingo!
04-09-2008, 07:57 AM   #48
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[QUOTE=moxfyre;210070]Perspective is not a function of focal length, only of camera-to-subject distance.

The perspective of almost any scene will be altered by the focal lenght, because of the optical qualities of the lens. This is a function of focal lenght. Wide angles tend to expand space and telephotos compress space. This is more noticable as the focal lenght moves away from normal focal lenght for the camera format. Of course the basic perspective of a scene is a product of the scene itself and the photographers point of view.

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04-09-2008, 08:38 AM   #49
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QuoteOriginally posted by Big Dave Quote
QuoteOriginally posted by moxfyre Quote
Perspective is not a function of focal length, only of camera-to-subject distance.
The perspective of almost any scene will be altered by the focal lenght, because of the optical qualities of the lens. This is a function of focal lenght. Wide angles tend to expand space and telephotos compress space. This is more noticable as the focal lenght moves away from normal focal lenght for the camera format. Of course the basic perspective of a scene is a product of the scene itself and the photographers point of view.
You're talking about barrel and pincushion distortion, right?

If you take a heavily-distorted image (e.g. from a fisheye lens) and correct it for rectilinear projection, you will see that it recovers the EXACT SAME PERSPECTIVE as any other rectilinear image taken from the same point.

So, I guess that a distorted lens gives the appearance of a different perspective, but it doesn't really change anything. If you take a picture an inch away from the left side of my face, my nose will get in the way of seeing the right side ... regardless of how you distort the image

04-09-2008, 08:58 AM   #50
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QuoteOriginally posted by moxfyre Quote
You're talking about barrel and pincushion distortion, right?

If you take a heavily-distorted image (e.g. from a fisheye lens) and correct it for rectilinear projection, you will see that it recovers the EXACT SAME PERSPECTIVE as any other rectilinear image taken from the same point.

So, I guess that a distorted lens gives the appearance of a different perspective, but it doesn't really change anything. If you take a picture an inch away from the left side of my face, my nose will get in the way of seeing the right side ... regardless of how you distort the image
I was talking about corrected lenses. A good example of this is the more desireable perspective of a portrait lens. The focal lenght of a good portrait lens changes with the size of the sensor or film format of course. A normal lens has little tendency to distort, but as we go wider we must be careful to avoid undesireable effects of wide angle syntrom. My point is that focal lenght is a major factor in capturing the desired perspective.

Dave
04-09-2008, 09:29 AM   #51
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QuoteOriginally posted by Big Dave Quote
I was talking about corrected lenses. A good example of this is the more desireable perspective of a portrait lens. The focal lenght of a good portrait lens changes with the size of the sensor or film format of course. A normal lens has little tendency to distort, but as we go wider we must be careful to avoid undesireable effects of wide angle syntrom. My point is that focal lenght is a major factor in capturing the desired perspective.

Dave
The only reason focal length affects the desired perspective is... because a longer focal length allows you to stand further away and still fill the frame

A portrait lens has a longer focal length so that you can stand further away from your subject and still capture them in detail. The slightly-flattened-face perspective is a function of the distance. Try it with a wide-angle lens from the same distance as you would take a portrait, and if you zoom in you'll see the exact same perspective.

But yeah, I think your basic point is right, although focal length is totally independent of perspective... in practice they are linked by the desire to photograph subjects of certain sizes from certain distances.
04-09-2008, 11:05 AM   #52
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We are all falling back into middle age.

A thread with 51 posts just to explain what a tangens is? And the few posters acting as teachers aren't even listened too?
04-09-2008, 01:36 PM   #53
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The only thing that I think matters is that we have a feel for the effects of the different lenses and use that knowledge to take better pictures. Digital really speeds up the learning process for me. I can experiment all I want and get instant results.

Dave

04-09-2008, 05:17 PM   #54
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I gotta say that this thread forced me to use the correct terminology to properly explain myself, which has consequently helped me assimilate other tangential factors into a bigger picture of understanding. Hooray for standards!

But really, I have, so thanks for the time spent all.

(dons his saber-toothed tiger skin coat and shambles back to his cave)


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