ISO question...

[alan breslow]

I am going to a school fair today. It is indoors. I keep the ISO at 200 most of the time. I will just be shooting snapshots. Is it ok to use 800 ISO so I get sharper shots of the kids moving around? thanks! Alan Sorry, the XT

[Jon]

What camera? ISO quality varies, getting progressively better as the cameras get newer in a line. But in general, I'd say to use whatever ISO you need to get a high enough shutter speed, even if it means going all the way to the top. A little noise can be cleared in post-processing - a little blur's harder (whether from camera or subject motion).

[Hellashot]

Yes, which camera? ISO800 on a 10D/Drebel is rather poor, but rather good on a 20D/XT. You'll want 1/200 shutter to try and freeze motion. I suggest an externa flash set to highspeed sync.

[Jon]

You won't need HSS. The flash burst is always shorter than 1/1000 sec, even at slow shutter speeds when using normal X sync. High speed (FP) sync is useful only if the surrounding available light is strong enough to render a 1/200 sec. setting overexposed, as it effectively increases flash duration by firing a series of bursts timed to cover the entire time the shutter gap is open. At X-sync or slower, the first shutter curtain fully opens before the second shutter curtain starts to close the shutter. The flash fires once, and exposes thwe whole scene so the sensor can see it. At faster speeds, the second curtain starts closing the shutter before the first curtain has fully opened, so a single flash can't illuminate the scene for the entire sensor - the flash will have to fire multiple times over the course of the exposure - more times at faster speeds since the gap between curtains is narrower then.

Flash will be OK as long as it's not distracting - you wouldn't want to use it while someone's performing, for instance. The lighting may be less pleasant than available, even after you factor in the noise; OTOH indoors in a gym, multi-purpose room or similar may mean white-balance problems from odd lighting (mixed fluorescents, mercury- or sodium-vapour for instance).

[glenhead]

For snapshots, I think you'll be quite satisfied with ISO800. They'll print up fine at 4x6. They may be a bit muddy compared to slower speeds in an older camera. You may want to take five minutes at the beginning of the event to see what kind of shutter speeds you can get with 400, or even 200 - the lights in some gyms can be bright enough to get fast shutter speeds with less-noisy ISO. A package like Noise Ninja can give stellar results at removing noise, if it's worth the $70 ($80?) to you.

One for-sure suggestion - use custom white balance (CWB). Take a shot of something white in the lights you'll be under and use that as your white reference - that'll give you correct colors in the camera and save massive amounts of post-processing time. Just remember to turn off CWB before your next nature series...

[Bob_A]

If you are using flash, Increasing ISO will help you select a larger f-stop number (smaller aperature) so that you can increase depth of field. Or, you can increase ISO to increase the distance you can shoot from using flash for the same aperature. Increasing ISO isn't going to help you stop action for the kinds of shots you described.

If you can't use flash, then increasing ISO will be your only choice to enable capturing the image at a higher shutterspeed to stop motion when ambient light is low.

Higher shutterspeeds with HSS sync (as Jon explained) can be useful if there is enough ambient light to result in a bit of ghosting of the subject or background motion blur. Personally, for snapshots, I use 1/250s and have never had an issue. Some examples where a higher shutterspeed MIGHT help are:

- You take a picture with your main subject properly exposed by the flash metering system at a lower shutterspeed, while an object is zooming by in the background. The main subject will be nice and sharp, but the underexposed object zooming by in the background will show some motion blur. This can sometimes be a very cool effect though, and you might actually want to reduce shutterspeed to make it more pronounced.

- You take a picture of someone with flash and lower shutterspeed and with reasonable ambient light while the person moves quickly. The resulting image can show a sharp image of the subject with a bit of ghosting.

- If when you take a image using flash and you want the background to fade to black to separate the subject from the background. To do this you have a choice of either increasing the f-stop number or increasing the shutterspeed.



If you are holding the camera fairly steady, and if flash is the main source of illumination then I would think that using HSS isn't necessary. For snapshots I typically set the camera to 1/250s just in case there is occassionally enough background illumination and leave it there.