A Flash Question I Couldn't Answer

[Noel_Carboni]

Hi Folks,

A friend of mine took a "bee on flower" macro with a Canon ring flash using a Canon 100mm macro at f/22 on a 40D set to ISO 200 in M mode with 1/200 second dialed-in.

For all the world it looks like there's motion blur in some of the bee's legs.

I can only surmise his flash was in High Speed Sync mode, which caused the light to be on the whole of the 1/200 second shutter open time.

I'm not near him, so I can't look over his flash settings nor do I own a Canon Ring Flash.

Anyone familiar with how one determines/enables/disables High Speed Sync mode on the Canon Ring Flash?

Thanks.

-Noel

[Ron Metz]

Hey Noel, I don't have an answer to your Canon ring flash question but it is good to have you participating again. Haven't heard from you in a while and thought that you may have retired and gone fishin.

Ron

[Jerry Skrocki]

The max flash sync speed of the 40D is 1/250 sec, so high speed sync would not need to be enabled if the shot was taken at 1/200 sec.

The high speed sync would be needed for speeds above 1/250 sec.

Looks like the bee was moving faster than the shutter speed setting.

[Doug_Kerr]

Hi, Jerry,

Originally Posted by Jerry Skrocki

The max flash sync speed of the 40D is 1/250 sec, so high speed sync would not need to be enabled if the shot was taken at 1/200 sec.

And, if set to ON, would not actually come into effect for that shutter speed.

[Ed Gerson]

The shutter duration was longer than the flash duration. Two photographs resulted.

[David_Buzzard]

Don't forget that it's not how fast an object is moving, but how long it takes the object to cross the field of view. That's why a race car that goes past a fixed camera needs a much higher shutter speed to freeze than a race car that's being followed by the camera.

If the bee is filling the frame, then the leg might be moving at high speed from one end of the frame to the other.

If the flash exposure is higher than the ambient light, it doesn't really matter about the shutter speed, just the flash duration. Your friend might want to dial up the ISO to shorten the flash duration.

David Buzzard's Technical Blog

[Jerry Skrocki]

With the Canon Ring flash MR-14EX and Canon Macro Twin Flash MT-24EX you push the + and - buttons simultaneously to cycle through the available flash modes. High speed flash setting is indicated by the icon with the H and flash symbol.

Having set the flash to high speed sync, the camera's shutter speed must be set higher than 1/250 of a second to activate the flash's high speed setting. This will get the faster (but weaker) pulse flash duration to effectively stop motion.

With this system, increasing the ISO speed increases the flash range but does not initiate high speed flash.