Question about flash sync

[MikeBcos]

Without using the high speed sync, will it causing any issue when the shutter is faster than 1/500 s with Nikon D40 with the flash? i.e. shadow / partially darken photo.

I thought it will, but I do not know too much about the electronically shuttered CCD as you mentioned.

The shutter opens the exposure starts and the exposure ends electronically. That means that for the full 1/4000th of a second the shutter is fully exposed, rather than a slit racing across the screen. The downside is this causes a big loss in image quality on CCDs and isn't possible at all on CMOS sensors I think but I'd need to check the latter.

I have never seen any loss of image quality when using high speed sync on my D40.

 

[Garbz]

Well you won't notice a change at all because it does it regardless if the flash is being used or not. The simple fact is a CCD suffers from something known as blooming, which is caused by an overload in the light that hits the photocell causing it to affect neighbouring cells (way oversimplification). When reading out data while light is hitting the sensor the photo cells are still receiving light. Now this may be a tiny tiny overall effect on the image quality until the sensor is completely saturated, but nevertheless it's something that is actively avoided on higher end CCD cameras.
High end cameras with faster and thus more expensive shutters get around this by simply ensuring the sensor is in the dark during read out preventing any bloom from occuring after the end of exposure.

What it looks like when taken to absolute extremes:

Taken on a D70, the result of a faster shutter than maximum exposure resulting in the blooming thanks to the sensor not being in the dark while being read out. Drop the camera below sync speed and use a ND filter or higher aperture if possible and the problem would disappear. In reality thought keeping a CCD dark during readout just increases the accuracy of it's saturated colours in non-extreme cases.
Source of image: http://www.tb-creative.de/sites/reviews/subsites/d70/d70_rev02.php