Preventing overexposure tomorrow in bad (no choice) light

<p>Hi. I really need some advice in a hurry. This is happening tomorrow. I've volunteered to photograph wildflowers for a master naturalist group. Classic 5D, 580ex and 24-70 f2.8 L USM. The members are collecting them for pressing - building herbarium. I will tag along as they identify (I shoot) and they dig it up. Photo gets archived with specimen.</p>

<p>Problem is we are meeting at 10 am and will walk sunny and wooded areas. I expect partly cloudy and a little breezy 10-20mph. Yikes! So in the woods it will be low tripod all the way. In the meadow-ish areas, I am hoping for some clouds and will shoot high shutter to avoid movement.</p>

<p>PROBLEM: Feels like a bunch of sunny pictures will need fill flash for shadows. Not expecting volunteers will reliably block sun for me. In these cases, I am afraid of overexposure versus excessive depth of field for high aperture number.<br>

Is it ok to raise ISO to prevent overexposure? Too low and plants will blur from movement. How to I ensure a workable balance?<br>

Thanks for any advice!</p>

<blockquote>

<p>Is it ok to raise ISO to prevent overexposure?</p>

</blockquote>

<p>Increasing ISO, given the same settings for aperture and shutter speed will increase your exposure, not decrease it.<br>

If you need a high shutter speed to stop motion, <strong>and</strong> a small aperture (larger f/ number) for depth of field, then increase your ISO till you get a correct exposure.</p>

<p><Chas>|<br /><br /></p>

<p>Bring a translucent panel of some kind to diffuse the light. Might also consider bringing a bit of white foam core to kick light into the shadows and block breeze. When you understand how to recognize and then modify light to suit your needs, photography becomes easy.</p>

<p>Kent in SD</p>

<p>Sorry for the confusing question. I meant lower ISO to prevent overexposure when a subject isn't moving and the light is bright (and I need fill). I didn't have time to test this as a possible cure for full sun with fill flash - overexposure. Auto exposure with this setup over-exposes very easily in full sun, yet I need shadows filled.<br>

Should I skip flash altogether and block sun? I am picturing some large plants and with bigger working distance. Maybe hard to get the sun blocked for larger subjects. Don't have a large diffuser. Maybe I should bring a bed sheet and have 2 volunteers hold it to block? Haven't confirmed in advance they will offer that.<br>

Expecting it will be tough to check the histogram when the camera body is in vertical orientation under the tripod - much of the time. Have angle finder and knee pad but access to the lcd screen will be a little challenging - probably time permitting.</p>

<p>Would it be better to leave the flash home and just block sun? </p>

<p>well... one last shot before I just wing it. Anyone? :-)</p>

<p>Anything that is color neutral and helps spread light is a diffusor. A white bed sheet will work fine.</p>

<p>Kent in SD</p>

<p>Show us how it went, after you process.</p>

<p>I guess yo are reading this too late, but all you need to do (for next time) for flowers in full sun is bring a black umbrella with you to shade the flowers.</p>