Controlling geometry with rear standard movements

[cunim]

Matt, distance was actually 1.0 m. Rear standard rotation was the same. Lens was the 138.

 

[MGrayson]

Matt, distance was actually 1.0 m. Rear standard rotation was the same. Lens was the 138.

So like this?

Backplane rotation


Lens rotation


Or is it some other combination or I have a swing direction wrong?

There won't be big geometry changes, but the region in focus is sensitive to all the orientations.

 

[cunim]

So like this?

Backplane rotation


Lens rotation

Or is it some other combination or I have a swing direction wrong?

There won't be big geometry changes, but the region in focus is sensitive to all the orientations.

Almost. The back is rotated opposite

 

[MGrayson]

Almost. The back is rotated opposite

So I'd expect to see this, where the geometry is little changed and the zone of focus is between the red lines. Consistent with your image.



There shouldn't be much difference between this and the lens swung. The wedge would start above the film plane instead of above the lens plane, as it does here. So it would come in at a slightly different angle, hitting the rangefinder less obliquely. That may be why the front of the lens is more out of focus in the film swing picture. Getting a bit too theoretical at this point.



Matt

 

[Shashin]

So I'd expect to see this, where the geometry is little changed and the zone of focus is between the red lines. Consistent with your image.



There shouldn't be much difference between this and the lens swung. The wedge would start above the film plane instead of above the lens plane, as it does here. So it would come in at a slightly different angle, hitting the rangefinder less obliquely. That may be why the front of the lens is more out of focus in the film swing picture. Getting a bit too theoretical at this point.



Matt

From my understanding, the second image is without movements and so the lens and the front of the camera is in the same plane of focus. The movements swing the plane of focus along the body of the camera, making the lens outside that plane and the lens is falling out of the depth of field. This probably would be clearer if the lens was wide open. Note, since the camera angle is high, there is another plane of focus interesting the camera at an angle vertically. Since this is fairly close, you don't have an expanding depth of field as you would at longer focus distances like when you use tilt in a landscape.

 

[MGrayson]

From my understanding, the second image is without movements and so the lens and the front of the camera is in the same plane of focus. The movements swing the plane of focus along the body of the camera, making the lens outside that plane and the lens is falling out of the depth of field. This probably would be clearer if the lens was wide open. Note, since the camera angle is high, there is another plane of focus interesting the camera at an angle vertically. Since this is fairly close, you don't have an expanding depth of field as you would at longer focus distances like when you use tilt in a landscape.

Oh, I'm being sloppy about a number of things. I should be finding the Hinge as well, but if I know where it's focused, that helps a lot in determining the focal plane . And, as you point out, the vertical aspect. I was just trying to get an idea of how different we would expect the two images to look. If the plane of focus were coming from wildly different directions, that would have been more obvious in the images. As for expanding DoF, very little of that wedge is in the final image - only the part near the rangefinder. Maybe I haven't thought enough about DoF in the near field, but I don't see off-hand why it shouldn't be a wedge (starting at the Hinge, not as I've shown it. Sigh.)

@cunim mentions the "front swung image", so I assumed that the back was left in normal position and the lens swung to get the rangefinder in focus. Again, all suppositions on my part.

 

[cunim]

Seems that I have been unclear about the conditions of my original post. It was just a casual comment on an interesting topic - how rear nonparallel movements compare between LF and MF sensors. I made a quick comparison between front and rear swing in a realistic product-type shot and was surprised at how subtle the perspective distortion was with MF. I seem to remember the effect being more pronounced on 8 x 10, but that was long ago and I could be wrong.

The first image is rear swing. The second image is front swing. In both cases, the swing is between 12 and 14 degrees. Tilt is not applied here (camera is tilted down a bit but front is parallel to rear), though I would usually combine (front) tilt and swing for this type of image (see attached for example of tilt + swing) - again with the camera tilted down.

. The need for tilt is seen in the soft focus of the rangefinder lens. F16 and a bit of tilt would help with that, but DOF is not the issue here.

As is common with this forum, some very knowledgeable people made comments that are useful and instructive. Thanks to @rdeloe for raising the topic, and to the respondents for trying to explain what is going on.

 

[MGrayson]

Seems that I have been unclear about the conditions of my original post. It was just a casual comment on an interesting topic - how rear nonparallel movements compare between LF and MF sensors. I made a quick comparison between front and rear swing in a realistic product-type shot and was surprised at how subtle the perspective distortion was with MF. I seem to remember the effect being more pronounced on 8 x 10, but that was long ago and I could be wrong.

The first image is rear swing. The second image is front swing. In both cases, the swing is between 12 and 14 degrees. Tilt is not applied here, though I would usually combine (front) tilt and swing for this type of image (see attached for example of tilt + swing).

View attachment 205949. The need for tilt is seen in the soft focus of the rangefinder lens. F16 and a bit of tilt would help with that, but DOF is not the issue here.

As is common with this forum, some very knowledgeable people made comments that are useful and instructive. Thanks to @rdloe for raising the topic, and to the respondents for trying to explain what is going on.

Thank you for the interesting example. It's not usual to get two such good images with differing movements. I agree that the geometry change looked too subtle. I don't *think* that should be sensor size related, but results beat theory every time.

 

[cunim]

By the way, I did try this with front and rear standards at vertical. With the requisite front drop (34 mm drop + swing!, amazing lens), loom remained subtle. In my own mind, I will file this away as "nonparallel rear movement creates only subtle looming with a long lens focused at minimum distance". As to any other conditions, rabbit hole indeed.

 

[MGrayson]

Apologies for Dead Horse Beating. The small magnification at 14 degrees was bothering me, so I did a rough theoretical "how much magnification do we expect" plot. The answer surprised me. Now this graph is accurate-ish only for an object right in front of the camera.

Anyway, for right in front, we get...



Yes, that's an increase of 3% for a 14 degree swing, 15% for 30 degrees, 41% for 45 degrees, and 100% (2x magnification) at 60 degrees. I doubt anyone swings by 60 degrees, but who knows?

But wait! How did that plant on the ground get so much looming for only 10 degrees tilt? The camera wasn't pointing at it, so it had, as far as the plot above goes, already tilted by the angle between staring down at the plant and pointing straight ahead. Add another 10 degrees and it could increase substantially.

Well, I feel better.

Matt

 

[rdeloe]

Apologies for Dead Horse Beating. The small magnification at 14 degrees was bothering me, so I did a rough theoretical "how much magnification do we expect" plot. The answer surprised me. Now this graph is accurate-ish only for an object right in front of the camera.

Anyway, for right in front, we get...



Yes, that's an increase of 3% for a 14 degree swing, 15% for 30 degrees, 41% for 45 degrees, and 100% (2x magnification) at 60 degrees. I doubt anyone swings by 60 degrees, but who knows?

But wait! How did that plant on the ground get so much looming for only 10 degrees tilt? The camera wasn't pointing at it, so it had, as far as the plot above goes, already tilted by the angle between staring down at the plant and pointing straight ahead. Add another 10 degrees and it could increase substantially.

Well, I feel better.

Matt

I'm just glad it's not a gigantic mutant succulent, and just a regular old "loomed" succulent.

 

[sbjornda]

But wait! How did that plant on the ground get so much looming for only 10 degrees tilt?

It simply grew! The photographer spent so much time fiddling with the camera movements that the plant had time to grow big!