Shooting MegaVision’s S2 digital camera back directly connected to a computer (tethered) will usually limit minimum shutter speeds at 125th/second. Shooting shutter speeds less than 125th will usually result in underexposure. This minimum shutter speed can be skirted which we’ll look into.
There is a reason why the minimum shutter speed limitation exists. The S2 uses the camera’s strobe synch circuit to tell the CCD when the shutter opens and closes. This is a simple and elegant solution that negates the use of the electrically driven camera body required by other manufacturers.
Since we’re using the strobe synch circuit for CCD notification, we’ve provided another port for connecting strobes, it’s located on the back of the PCI card in the computer. Find it under the data cable connector where the camera back connects to the rear of the computer. You’ll also notice the same thinking in our BatPac™ design, we provide a strobe connection port on the BatPac's™ top panel because we use the camera’s strobe synch circuit for CCD notification.
This strobe trigger design has a set amount of delay as part of the circuitry, it takes certain amount of time for the software to acknowledge the shutter’s contact closure (signaling the full open shutter) which tells the software to send a signal to the PCI card, where the strobe is connected, telling the strobe to fire. This delay on most cameras will find partial shutter closure when speeds faster than 125th are used. You may discover focal plane shutters have a slow synch speed and will therefore not allow even the 125th selection.
Typically you’ll find the strobe’s flash duration very brief and will actually determine the exposure time of the capture. If however you’d like to shoot faster speeds than 125th you may do so with the use of a hot shoe. Several host cameras support hot shoe implementation. This circuit will time the strobe firing in concert with the shutter contact closure, skipping the delay induced by the normal strobe timing. You may fire the strobes via the hot shoe with a radio (or IR) slave, or you can use a small, portable strobe which will notify most standard pack mounted slaves. Be aware that you must never rig a Y connector into the camera’s CCD strobe synch circuit for strobe triggering. The S2’s delicate circuitry will be damaged by the trigger voltage inherent in most strobe triggering circuits. If you have questions on the use of hot shoe strobe synchronization, forward your questions to MegaVision Technical Support.