Slanted subject in focal-plane shutter images.

[wfooshee]

We've all seen the old race car images with the cars slanted forward. That "leaning" came to be equated with speed, to the point that fast things in cartoons were drawn leaning forward.

We all (probably) know what causes this... it's the fact that the shutter travels across the frame slowly enough that the subject changes position during the exposure. This is a fairly quick shutter speed, as there is no motion blur, but the slit of the shutter took long enough to cross the frame that the images distorted as the car moved. Had the photographer been panning with the car (which would probably have been quite a feat with the cameras of the day,) the car would be more or less correct, but everything in the scene would be leaning the opposite direction.

I actually managed to capture the effect myself at the Blue Angels Homecoming show in 2017. I had a bleacher seat, and of course for the sneak pass of #5, as he comes past at nearly 700 miles per hour at only 50 feet of altitude, I had the camera going at continuous shutter. My shutter speed was 1/2000. One of my shots caught the jet passing those annoying speaker stands that kept getting in the way, but look at it carefully: the vertical posts of the scaffold are leaning backwards!

Doing a little bit of math, something travelling at 700 miles per hour goes a tick over 6 inches in 1/2000th of a second. I was obviously panning as he passed. Doing some more mental gymnastics (and a little guesswork on subject distances,) I figure the speaker stand was about half the distance to the jet, maybe less. Since it's about half the frame high, I'm going to say that its perceived "lean" is between two and three inches. In other words, the top of a post is two or three inches off of vertical with the post at the bottom of the frame, as a result of my camera motion during the exposure. Also, I want to say that the camera was moving fast enough to induce motion blur, even at 1/2000th of a second. I wasn't sure how much was motion blur, and how much was just too close to be in focus like the jet, but the vertical posts are fuzzier than the horizontal elements. To me, that's motion blur.

EDIT: I just realized I completely misfigured the timing! Yes, the shutter was 1/2000, but the physical motion of the shutter travel takes 1/250th or thereabouts, the camera's flash sync speed. So the exposure time, start to finish, was eight times longer than I figured above. In 1//250th of a second, 700 mph is enough to go that tick over 4 feet. If the speakers are 1/3 the distance to the jet, then the offset of the poles, top to bottom, could be a foot and a half, maybe just a foot. Again, no idea how far away either one is. (The EXIF data for focus distance was 4.9 MILLION meters, so probably incorrect.)

 

[Golem]

We've all seen the old race car images with the cars slanted forward. That "leaning" came to be equated with speed, to the point that fast things in cartoons were drawn leaning forward.

We all (probably) know what causes this... it's the fact that the shutter travels across the frame slowly enough that the subject changes position during the exposure. This is a fairly quick shutter speed, as there is no motion blur, but the slit of the shutter took long enough to cross the frame that the images distorted as the car moved. Had the photographer been panning with the car (which would probably have been quite a feat with the cameras of the day,) the car would be more or less correct, but everything in the scene would be leaning the opposite direction.

I actually managed to capture the effect myself at the Blue Angels Homecoming show in 2017. I had a bleacher seat, and of course for the sneak pass of #5, as he comes past at nearly 700 miles per hour at only 50 feet of altitude, I had the camera going at continuous shutter. My shutter speed was 1/2000. One of my shots caught the jet passing those annoying speaker stands that kept getting in the way, but look at it carefully: the vertical posts of the scaffold are leaning backwards!

Doing a little bit of math, something travelling at 700 miles per hour goes a tick over 6 inches in 1/2000th of a second. I was obviously panning as he passed. Doing some more mental gymnastics (and a little guesswork on subject distances,) I figure the speaker stand was about half the distance to the jet, maybe less. Since it's about half the frame high, I'm going to say that its perceived "lean" is between two and three inches. In other words, the top of a post is two or three inches off of vertical with the post at the bottom of the frame, as a result of my camera motion during the exposure. Also, I want to say that the camera was moving fast enough to induce motion blur, even at 1/2000th of a second. I wasn't sure how much was motion blur, and how much was just too close to be in focus like the jet, but the vertical posts are fuzzier than the horizontal elements. To me, that's motion blur.

EDIT: I just realized I completely misfigured the timing! Yes, the shutter was 1/2000, but the physical motion of the shutter travel takes 1/250th or thereabouts, the camera's flash sync speed. So the exposure time, start to finish, was eight times longer than I figured above. In 1//250th of a second, 700 mph is enough to go that tick over 4 feet. If the speakers are 1/3 the distance to the jet, then the offset of the poles, top to bottom, could be a foot and a half, maybe just a foot. Again, no idea how far away either one is. (The EXIF data for focus distance was 4.9 MILLION meters, so probably incorrect.)

Play with a Speed Graphic shutter and youll see why the really obvious effect, such as the racing car you posted, just doesnt occur with small cameras and modern FP shutters. Those big old shutters are downright lazy so their top speed is a ridiculously narrow slit thaz just not moving at any great speed.

BTW, panning was no problem at all. Ben Dare & Don Datt. And if you panned it just right, you got your subject leaning forward AND the backround also leaning but in the opposite direction.

The situation where panning really could get tricky would with a Grafic Reflex ! Maybe thats why Lartigue barely caught his subject the pic below ?!?
.

 

[wfooshee]

Play with a Speed Graphic shutter and youll see why the really obvious effect, such as the racing car you posted, just doesnt occur with small cameras and modern FP shutters.

Yeah, I was just amazed that I caught the effect at all when I saw it. I guess 700 mph shows a "significant" amount of movement, even in 1/250th of a second.