[bymy141]

Image the following setup:

- You have a close by object that travels horizontally.
- It moves within the frame of your camera from left to right in 0.05 seconds.
- Your camera's fastest flash sync time is 1/200 sec (0.05 sec).
- You are shooting at your fastest shutter speed (1/4000 or 1/8000)

I would expect the object to be smeared across the picture.
Since the shutter will start to traverse down and ends it cycle in the same time as the object moves from left to right.

This is how it works, right?
I've never seen any proof of this in any of my photo's.
Anybody else?

- Bert

[an49]

maybe I'm wrong but if you choose that shutter speed,
the shutter will open and close before the flash even thinks about flashing.

As far as I know the durance of the Flash is much shorter (about 1/2000 - 1/5000 depending on the flash).
The time 1/200 (1/180 on my K100) is the shortest time that the camera is able to interact with the flash.

You may chose a shutter time like 1/60 or longer the durance of the flash will
sharpen the object.

greets an49

[alohadave]

Here's how you do this:

Set your shutter speed to 1/180th or slower.
Set your flash at the power needed to light the subject.
Trigger the camera. Either manually or with some sensor.

Your camera will not trigger the flash above 1/180 anyway. And you do not want to use HSS because you will still get a blurry shot of the object traveling across the frame, it will just be lit.

[bymy141]

maybe I'm wrong but if you choose that shutter speed,
the shutter will open and close before the flash even thinks about flashing.

As far as I know the durance of the Flash is much shorter (about 1/2000 - 1/5000 depending on the flash).
The time 1/200 (1/180 on my K100) is the shortest time that the camera is able to interact with the flash.

You may chose a shutter time like 1/60 or longer the durance of the flash will
sharpen the object.

greets an49

I did not make myself clear enough. Sorry about that.

The question is not how to make flash photos of a fast moving object.
It is not about taking flash photos at all in fact.

It is about photographing fast moving objects at close range with no flash.

It is considering that a focal plane shutter (as in our DSLR's) can only be completely open at relative long shutter speeds.
You can determine that minumum duration by looking at the highest flash sync speed.

Have a look at the video in this post: https://www.pentaxforums.com/forums/pentax-dslr-discussion/111375-say-what-k1...es-second.html
You can see that the shutter takes about 1 second in that movie to go down.
At 5000 frames a second, slowed down to 25 frames a second that is 1/200 sec = 0.05 sec. That matches the maximum flash sync speed.
So, the maximum flash sync speed of a camera can tell you the time the camera shutter needs to traverse down.

Looking at the video clip again, you will see that the shutter is open by a small area only! (1/4000 sec for all pixels of the entire photo)
For 1/4000 sec in a 1/200 sec cycle time, the opening should be 1/20 of the entire plane.

This means that during the shutter cycle time (0.05 sec) a fast object will still move relative to the camera's position.
While the opening in the plane moves down, the object will move to the right.
When the object moves so fast that it will traverse from left to right in the same time as the curtain travels from up to down, you must see a very morphed picture of the object.

I'm wondering if anybody has captured a picture like that.
The object should be looking stretched from the left top to the right bottom.
I've tried to make a picture a 90mm lens, moving fast past some vertical blinds, without any success.
What is wrong with my reasoning?

- Bert

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Last edited by bymy141; 08-22-2010 at 07:39 AM.

[goddo31]

Hi Bert,
Check out this article on wikipedia for some examples: Focal-plane shutter - Wikipedia, the free encyclopedia

[bymy141]

Hi Bert,
Check out this article on wikipedia for some examples: Focal-plane shutter - Wikipedia, the free encyclopedia

Thanks jason, the blades on the helicopter is the thing I was looking for!

- Bert

[goddo31]

You're welcome
I have read that article before, so I thought that was what you were talking about.
It seems quite logical however I have never seen it in a photo I have taken, yet. That can be partly explained by the subject of course. That helicopter photo is interesting though!

[alohadave]

How's this for coincidence, the Flickr blog featured rolling shutter pictures today.

Rolling, Rolling, Rolling Shutter Flickr Blog

[goddo31]

How's this for coincidence, the Flickr blog featured rolling shutter pictures today.

Rolling, Rolling, Rolling Shutter Flickr Blog

I just noticed that and came back to post it!
The picture with the bent aircraft propellers freaks me out a bit...

[bymy141]

Wow!
Very nice!
I like this one as well:



Now I have to try make a few myself...

- Bert