Speedlight flash -will it help?

John8

Hi all, wonder if anyone can help me, I am wondering if using an external flash, i.e. Canon 480ex, will help freeze the image, i.e. give sharper image - portrait in particular, at slow shutter speed, i.e. down to 15th of a sec and the subject are not moving actively?

John.

zoomer

Yes the sync speed of flash is usually 250 or so. Does freeze the subject.
Do you have a specific application in mind?

ziggy53

John8 wrote: »

Hi all, wonder if anyone can help me, I am wondering if using an external flash, i.e. Canon 480ex, will help freeze the image, i.e. give sharper image - portrait in particular, at slow shutter speed, i.e. down to 15th of a sec and the subject are not moving actively?

John.

If you are adding contributory ambient light to the flash exposure, and if the exposure duration is 1/15th, flash will not reduce the subject motion from the ambient contribution.

Zoomer is correct in that the flash duration itself is generally short, and flash sync is generally 1/200th-1/250th (for many/most dSLRs). Using the flash sync shutter speed and ISO 100 will often help to subdue the ambient light contribution (except in direct sunlight and with a large aperture). Some professional dSLRs will sync to 1/300th and some older dSLRs, based on CCD designs with an "electronic shutter", may sync to "very" fast shutter speeds:

http://strobist.blogspot.com/2007/05/hacking-your-cameras-sync-speed-pt-1.html

Additionally, some cameras and compatible flashes have a special mode, FP/HSS (Focal-Plane and High-Speed-Sync, respectively) that can allow extremely fast shutter sync speeds, but only at relatively short working distances. Still, FP/HSS mode can be effective in helping to control ambient light (But it will not stop subject motion any better than normal flash sync speeds.)

http://www.dgrin.com/showpost.php?p=1497181&postcount=6

pathfinder

Why is your shutter speed so long? Is the ambient light that dim? If so, why not add more light, and use a faster shutter speed? Or is the long shutter opening being used to capture flowing movement in the image?

2nd curtain flash is used to allow the ambient motion to display in the image, with the flash firing just before the shutter closes, so that the image is mildly blurred right up to the moment the flash fires at the end of the exposure, and that portion of the image is sharp. Think of a moving car with the car lights blurred due to movement, and then the car captured sharply by the brief light flash from the strobe.

John8

Thanks all for your prompt replies.

The reason I ask this question is because when I was in Hong Kong for holiday I saw photographers taking picture of tourists then print them out for a small fee. What baffle me is the photos were taken along the embankments at night (almost pitch black) with one off camera flash, the result is amazing lights from Hong Kong skyscrapers in the background and the subject is correctly expose. Am I correct in thinking that they used slow shutter to expose the background and then the flash to fill in the subject. If this is the case, they must use a very slow shutter speed. I couldn't test this out myself because I didn't have my flash at the time.

kdog

^^ Yup, you've got it right.

This is a 1/8s exposure.


This is a 5 second exposure.


Here's essentially the same shot as above where you forgot that the shutter was still open and moved the camera.


Shawn is blind, which might explain why he chose that latter shot for his album cover.

Cheers,
-joel

John8

Thanks kdog for sharing these photos. They are stunning!

John8

Oh kdog, forgotten to ask your photos are they taken with or without tripod?

pathfinder

Joel's 5 second exposure was on a tripod ( I would bet ), ar at least braced firmly on a solid object. He may have hand held at 1/8th sec with an IS lens, but a tripod based camera will give much sharper images, especially with a cable release and mirror lockup.

One way of avoiding the long exposure is to raise your ISO up much higher, use a wide aperture. The higher ISO effectively makes your flash much, much more powerful also - eg: raising the ISO yields a higher flash guide number.

John8

With high iso and wide aperture, will the flash help to reduce the noise? I am sure there will be some elements of noise but just wondering if the flash will make some difference as compared to no flash.

pathfinder

Noise at higher ISOs relates to what specific camera you are using, and I did not see in your profile what camera body you are using.

I can show you images I shot at ISO 1600, that will print quite nicely, shot with a 40D, or a 7D. Look for grain in this image. I would not recommend that ISO if your goal is 16 inch by 24 inch prints, but for 8x12 inch prints you should be just fine.


A very important tip for shooting high ISO, like 1600, is to Expose to the Right, eg: avoid under exposure. If you shoot at high ISO, under expose, and then use the Exposure slider in Raw processing to lighten things up, you WILL see more much noise.
If the noise offends you in your background, NoiseWare will make short work of it, especially in the blue channel.

Most smaller point and shoots will not fare well above ISO 200 or so.

John8

Thank you for your tips pathfinder. I am using a Canon 50d, got various cheap lenses that I am too shy to mention, :-( Anyway with this camera I am able to push up to 1000 iso that i am happy with, beyond this it a hit and miss - i.e. depending on the type of background. Now that you've mentioned software fix, I think it probably better in future if needed I push the iso as high as I can get to get a fairly useable pictures than a really dark ones or a blur ones.

Thanks again guys.

kdog

pathfinder wrote: »

Joel's 5 second exposure was on a tripod ( I would bet ), ar at least braced firmly on a solid object. He may have hand held at 1/8th sec with an IS lens, but a tripod based camera will give much sharper images, especially with a cable release and mirror lockup.

Correct on all accounts. I did hand-hold the 1/8th second shot, and I believe it's a little soft because of it. That's already ISO1600, and wide-open at F4, btw.

spinero

The flash will stop most motion if the person is not lit by any other light source that registers exposure. Essentially, if the person is dark without the flash, you are pretty safe with the flash. Don't worry about numbers. They change with every scenario. Worrying about what the exposure settings on a photo is like worrying about the key of a song. It won't help you sing it when it is your turn.