On lens focal length, Perspective, DOF and more.. PT- 1

[Bernice Loui]

Question of lens focal length, perspective and DOF constantly appears on LFF. To address this seemingly on going question, these pages were taken from a Canon Lenswork book published in the 1970's.. Yes, the lens focal lengths and such are 35mm roll film centric yet applies to image making in cinema, video, 35mm_120 roll film, Digital of all sensor sizes and all sheet film view cameras.. The basic rules apply, only the "normal" lens focal length for a given image recorder size be it digital or film remains the same..

Lens perspective changes driven by lens focal length. Note the change in background when the foreground object (gal) size is held constant.. This was done by changing the lens focal length then moving the lens/camera forward or back to hold the foreground object to the same size.







Bernice

[Bernice Loui]

On lens focal length, Perspective, DOF and more.. PT- 2

More on image perspective -vs- lens focal length.


Examples of fixing the lens/camera position as the lens focal length is changed. Note the image examples of how the image changes based on lens/camera height..





Bernice

[Bernice Loui]

On lens focal length, Perspective, DOF and more.. PT- 3

DOF/F, Depth of field, Depth of focus.. how lens exposure aperture affects the image recorded. Note the illustration of lenses having a single point/plane of focus. All else is rendered as perceived to be in focus, how much depends in the exposure aperture, distance from lens to subject and much more.. All these factors figures into lens choice, image goals and all related.. This is where a view camera has very real advantages over fixed box camera with a fixed lens (yes, tilt/shift lenses can be applied but still does not have the capabilities of what a GOOD view camera/lens combo can do).. The ability of a view camera to exploit camera movements limited by the combo of lens/camera coupled with the variety of lenses available (view camera lens choices degrades greatly as the sheet film size goes up. Once past 8x10, lens choices become increasingly smaller) are just two of the prime advantages of a view camera. If these two prime advantages are not fully utilized, why bother using a view camera.. "sharpnes"s ala that aspect of image quality alone is not enough..

It is also why the idea of chronic f22 is limiting and not always ideal as is the entire f64 ideology of everything in the image always to be in perceived focus... another creative/expressive image limiter..


Bottom of this page has a good illustration of lens point of focus, their cones related and the concept of DOF/F.. or why smaller lens apertures does not increase "sharpness"..









Bernice

[Mark Sawyer]

Lens perspective changes driven by lens focal length. Note the change in background when the foreground object (gal) size is held constant.. This was done by changing the lens focal length then moving the lens/camera forward or back to hold the foreground object to the same size.

I'll offer that "perspective" is synonymous with "point of view". When you change where the camera/lens is, you've changed the perspective because you're literally seeing the scene from a different point of view. Changing focal length while staying in the same place is just in-camera cropping.

Changing the point of view to keep the primary subject the same size changes both the angle of view and the apparent compression of space. That is, switching from a short to a long focal length will give the traditionally more flattering perspective of the subject's face, and also compress the subject into a flatter, more restricted angle of view of the background.

Moving the camera while shooting a video while simultaneously zooming to keep the primary subject the same size makes you feel like you're in an Alfred Hitchcock movie.

[ic-racer]

The only way to change perspective (the relationship between objects) is by moving the front standard (lens) to a different position in space.

Likewise, any movement of the front standard changes perspective (the relationship between objects).

[Bernice Loui]

Stanley Kubrick was famed for applying this to filmmaking. Notable was the opening scene in Clock Work Orange..

Combined large range zoom with the camera on a rail sled..ala Zolly_Dolly...
https://www.youtube.com/watch?v=HI-mDTdeKR8

Or Barry Lyndon:
https://www.youtube.com/watch?v=maz9KP76VvI

Zoom lens is not the same as using a Dolly where the lens focal length is fixed then the camera/lens is moved:
https://www.youtube.com/watch?v=7QeMMF7J2OU


Bernice

I'll offer that "perspective" is synonymous with "point of view". When you change where the camera/lens is, you've changed the perspective because you're literally seeing the scene from a different point of view. Changing focal length while staying in the same place is just in-camera cropping.

Changing the point of view to keep the primary subject the same size changes both the angle of view and the apparent compression of space. That is, switching from a short to a long focal length will give the traditionally more flattering perspective of the subject's face, and also compress the subject into a flatter, more restricted angle of view of the background.

Moving the camera while shooting a video while simultaneously zooming to keep the primary subject the same size makes you feel like you're in an Alfred Hitchcock movie.

[Drew Wiley]

And the moral of the lesson is, always have a Handl fugue playing over and over in the background if you want to make a dramatic picture with seemingly inappropriate lenses...

[Tin Can]

Here I am shot FF D750 Nikkor 135mm AF f/2 DC

At 6 feet, seems it did not make me thinner

I had ballooned to 230lb from my DR advice in only 3 months! Dr decided to teach...

Took years to get it off, now 165 lbs

That lens I like, but it cannot do miracles

I will add another with that lens when...

2009 Me by TIN CAN COLLEGE, on Flickr