Slow Sync Flash in Bright Light

[martinslade]

I was wondering if anyone can help with advice on this. I need to shoot mountain bikes in bright light at 1/30th sec to get some background blur and want to pan + fill flash to get some detail in the subject. The bright back light from trees/sky is causing small apertures to keep slow shutter so do I need extra flash power to get the right balanced effect? My flash will be mounted off camera 3-4m from subject and I will be low shooting up about 2m out. My flash is rated 36 and I will probably be at 100 iso. Any help much appreciated... thanks...

 

[StudentOfLight]

I was wondering if anyone can help with advice on this. I need to shoot mountain bikes in bright light at 1/30th sec to get some background blur and want to pan + fill flash to get some detail in the subject. The bright back light from trees/sky is causing small apertures to keep slow shutter so do I need extra flash power to get the right balanced effect? My flash will be mounted off camera 3-4m from subject and I will be low shooting up about 2m out. My flash is rated 36 and I will probably be at 100 iso. Any help much appreciated... thanks...

Are you trying to overpower full sun or is there some other ambient light source? (I assume full sun)
What camera body are you using? (Minimum ISO?)
How did you get to a guide number of 36? (I assume 600EX-RT at 35mm zoom?)
Are you fixed to 1/30s? (Could you use a faster shutter speed?)
Given your constraints, I don't see how you can make it work.

According to my (self-made) exposure calculator...given ISO-100, 1/30s, you will need to shoot at f/29 to get a proper ambient exposure in full sun.
(GN) / (f-stop) = range
(36)/(29) = 1.2 m

At f/29 there's a lot of diffraction so for a sharper aperture you'll need to use an ND filter. With a 3-stop ND filter you can open your aperture wider to f/10. Note, ND filters do have a negative impact on image quality and viewfinder experience and AF performance. The big problem though is that your flash still only illuminates properly up to 1.2m.

In order to counter this one could gang together multiple Speedlites, (e.g. http://www.bhphotovideo.com/c/product/897247-REG/westcott_2223_bruce_dorn_triple_threat.html) to boost your flash power. I reckon that you will need 5-6 speedlites to get sufficient light to properly illuminate the subject at a distance of 4m.

I assume that mountain bikes are moving relatively fast so maybe 1/125s can still work? If it can, then trading slow shutter for larger aperture size allows you to:
a) gain flash range or
b) reduce recycle times or
c) gel your flash

So, sorry I don't have a magic bullet to solve the problem, but there are a few strategies at your disposal. Think of it this way, if it was gonna be easy then anyone could do it and the end result would be less valuable.

P.S. See what Canon EoL Tyler Stableford does here: https://www.youtube.com/watch?v=KaALe0w992E

 

[Pookie]

No matter what you're going to struggle with the speedlite. I do these types of shoots in Tahoe for snowboarding or summer bike races. The only way to really get this to work, at least for me, is using my Elinchrom Rangers at near full power... 1100ws. You can rent them in the bay area of California. Even then it takes a bit to setup and get the right light.

 

[risc32]

Without knowing a bit more details (are they in full sun, actually now that I think of it, put them in the shade, seriously) can't say with certainty, but I don't see you having too much of a problem.
when you say you like 1/30th I'm not going to say to go 1/125th or something...?? 2-3m , flash to target distance. Might be fine. What flash are you using? Battery pack or aa? That one doesn't matter for output, just curious. So 1/30, iso at the minimum, fstop adjusted to your desired background exposure, get the flash as close as possible, and dial it up (manual mode for everything) until you are good. I bet you will be good. If you do need more juice, and a power outlet is nearby you should look into a head/powerpack or monolight setup for this. Much more power than any battery operated unit and really if you buy used no more pricey than a very expensive top end handheld unit. Cheaper actually. My speedotron system could probably be had used for about the cost of a 430.

 

[martinslade]

Been thinking more about this since your (insightful) posts/comments... thank you all for that..! Bright sun is worst case really. There is some broken tree cover that will give some shade and if weather is typical for UK might be cloudy. I reckon might get away with 1/60th as riders will be passing at reasonable speed. I also might be able to get speedlight a bit closer maybe 2-3m and might be able to borrow a second slave unit.

The area is on a slow bend so riders will be cutting in close. Any sun will give high back lighting above tree-line so was wondering if best place for flash unit is head-on to approaching riders (might be a dazzle problem) or 70 degrees to their inside on the bend? I will be shooting low at about 45 degrees to their trajectory.