D40 Fault or Feature

[ian_rose]

<p>While Practiceing useing 2 flash units off camera (both generic) 1 triggered useing a AS-15 and a sync cable and the other fired useing optical sync. I found that the camera will sync with the flash without leaveing a shutter blind mark on the image (ie black band accross the image )right up to 1/4000 . When useing the onboard flash max speed is 1/400. Any comments.</p>

<p>Ian R</p>

[alan_huett]

<p>This is a (bonus) feature - there is no full-speed mechanical shutter on the D40, so the shutter is simulated for high speed by "gating"the sensor electronically (basically the sensor output is only recorded for the short period required, but the sensor is exposed for a longer time by the slower-moving shutter). Therefore it will sync at high speed without needing a focal-plane sync mode. However, I think you lose some flash power, since the "gating" can be shorter than the flash pulse itself.<br>

You can trick the camera into doing this with on-camera flash by covering all but the center contact pins, the flash will trigger, but the camera will not recognise that it is mounted. The untricked on-camera sync speed is limited by the firmware to 1/500 to avoid light loss due to "missing" the main flash pulse and to give some headroom for the trigger timings. I am not sure what happens when you use the speedlight FP-sync high-speed modes with the D40, but I assume it works just fine.</p>

[Matt Laur]

<p>Yup, that's a happy byproduct of how they cut the corners around - at that price - making a mechanical shutter that can work at those speeds. There are some (insignificant, for most people) down sides to that design, but it's one of the reasons that some sports shooters keep a D40 around - so they can use it to freeze action in different ways.</p>

[akira]

<p>I considered it was a bonus, but, according to my experiment with a flash set to manual/full power, the images gets more underexposed as you go faster than 1/500 (nominal max synch speed, not 1/400), probably because the flash duration was longer than the shutter speed.</p>

[epp_b]

<p>Yup, this is an incidental "feature" and, unless I'm overlooking something, Nikon <em>could</em> have engineered to sync it all the way up to 1/4000th with iTTL, but that would make the sync <em>too</em> much higher than that of pro bodies. The D70, D50 and their respective variants also have this "feature" and it's why I plan to keep my D40 even if/when I upgrade to something else.</p>

<p>It's also nice to be able to sync up to 1/3200th when using off-camera RF triggers. It makes balancing available light with artificial light very easy without affecting depth of field.</p>