Flash for Olympus 510

[Tom Wiggins Photography]

<p>I'm looking to get a flash for my Olympus 510. I've been using the on-camera flash and it's just does make it. I do see Guide Number like 98' at 50mm or 177' at 105mm, what this all mean? Thank you for your help. Tom</p>

[andrewg_ny]

<p>Refers to the maximum available flash power. The formula is:<br>

Aperture (f-stop) = GN / flash-to-subject distance</p>

<p>GN 98' means that the flash is powerful enough to provide full illumination using ISO 100 with an f/1.0 lens with a 'normal' angle of view (like a 50mm lens on a 35mm film body) to a range of 98 feet. On your E-510, that would be a 25mm lens . Note that using higher ISO will increase this range but slower lenses (smaller apertures) will decrease it. The GN is generally higher for telephoto lenses because these flashes feature zoom heads that concentrate output to a smaller coverage area. </p>

<p>Note that these calculations assume direct flash--if you're bouncing the flash be aware that more power is required because the distance from flash to subject increases, plus light loss due to less-than-perfect reflectivity of the bounce surface.</p>

<p>When comparing note that some flash manufacturers may overstate their units capabilities, and also be aware that many will quote in meters rather than feet. Note that your E-510's built-in flash is GN12 with a coverage of (I'm guessing) 28mm (in 35mm film terms). This is probably expressed in meters rather than feet (39'), but there's no zoom head so you get the same GN no matter how your lens is zoomed. </p>

[Tom Wiggins Photography]

<p>Andrew: Thank you, your explaniation was very helpful. Tom</p>