A word about speed

Even with the latest improvements its unlikely that I'll every be able to run my experiment fast enough for real real time (need 10's of kHz for that). Still, 50 Hz is better then 3. There are several factors that affect the temporal sampling rate of my experiment. Most of them are interrelated, so it helps to sort out just what impacts what.

Essentially, there are 3 time-comsuming operations that have to be completed each iteration. Ignoring the time to calculate control signals, these are: Commanding the DM, capturing the WFS image, and processing the image to generate the slope vector.

Sending DM Commands:
This is basically fixed around 100 Hz currently. I'm still not sure if the actuators actually reach their steady state positions at that speed, hopefully I'll have that sorted out next week. The unknown here is that the fwrite command used here can time out, basically crashing the whole enchilada.

Capturing WFS image:
As I found out last week, the frame rate of the WFS is a function of the frame size and the shutter speed. The frame size dictates the number of sub-apertures used, and hence determines the spatial sampling frequency. Intuitively, reconstructing (and hence controlling) higher spatial frequencies means a slower frame rate.

Short shutter times also increase the frame rate, but only up to a certain point. Beyond that, the frame size basically determines how fast the thing can go. Generally, the idea is to select the minimum shutter speed necessary to accurately image the sub-apertures.

Computing Slope Vector:
Again, this is a function of how many sub-aperatures are being used. I'm not exactly sure how this varies though since its cumbersome to alter the code every time for a new image size.

Clearly a lot of these parameters are fixed by the experiment. The DM only has 31 actuators, so there's a limit to the required spatial sampling frequency. Whats more, for a given laser the shutter speed can just be set to the smallest value that still allows the centroid algorithm to work. That basically leaves the WFS frame size as the only parameter that can effectively be varied. I'm hoping to write up a little script this weekend to see how the overall frame rate is affected by this.