In my lab I have two cameras, the Canon T2i and the Canon T3i, which are without their standard lenses. Instead they are mounted on a microscope. To capture the images of my samples, I set the camera to the manual mode and then I press capture button in the
EOS Utility software which is installed on a nearby computer.
The images thus captured, as far as I can discern with my limited senses, seem to have a consistent lag between the mouse click and the actual capture. Now, I am trying to automate a process of capturing 100 images over a period of about 200 seconds (198 seconds to be more accurate). I will be using the technique detailed on this link. However, instead of the manual switch I will be using a micro-controller (the controller is extremely accurate — so, for this problem, please neglect the µs errors arising due to the controller).
Concentrating on the milliseconds, I want to figure out how much would be the shutter lag (i.e. the time gap between the image capture and the trigger command issued by the micro-controller). The shutter lags for the cameras are noted on the following links:
Canon T2i : http://www.imaging-resource.com/PRODS/T2I/T2IA6.HTM
Canon T3i : http://www.imaging-resource.com/PRODS/T3I/T3IA6.HTM
The information provided there has become a source of confusion. I hadn't read about prefocus before, but from what I have understood, prefocus is the shutter lag after half-pressing the trigger. Thus the photographer "prefocuses" on the target before capturing the image. Why is there a difference between the shutter lag times for prefocus and for manual focus (in the case of each camera)? Is there an underlying difference between the mechanisms of prefocus and manual focus? I would have assumed that after the prefocus operation is complete the camera will react the say way as if it was in manual focus. After all, in both cases, the object is already in focus when the camera receives the command for capturing the image.