Open loop timing

[Michael-F-Ellis]

First of all, thanks for creating and documenting this project!

I'm working with other colleagues at a local maker space to build an OpenScan system for use by our members. We've pretty much decided in favor of the Raspberry Pi controller instead of the Arduino version.

One remaining concern involves users who want to program a scan pattern into the controller and then set up a smartphone to take shots at a fixed interval, i.e., without explicit shutter control.

From the manual, it looks as though that can be accomplished in the user interface by setting the mode to External and Time per Foto to an appropriate value and ignoring Release time since that output would be unconnected. Is there any problem with doing that?

Without digging into the code, my impression is that Time per Foto does not include the time for the stepper to move the axes to the next position. Is that correct? If so, is it reasonable to assume the transition time will be more or less constant, i.e., something that can determined empirically and added to the time interval on the camera side?

Thanks!

[OpenScanEu]

Hi Michael, sorry for getting back so late, but I am finally there.
at least without changing the 'toolpath', this approach would not be very viable, as the time between each position varies quite a bit. A while ago, I optimized the movement pattern, so that the camera positions are equally spaced. (see the first image of this post: https://www.reddit.com/r/OpenScan/comments/k0q2gy/new_routine_for_equally_spaced_camera_positions/)
The 'downside' of this approach is, that the movement feels kinda random and sometimes the turntable moves almost 180° between two positions, sometimes it almost does not move at all.

But why would you use a constantly timed triggering mechanism anyway? The firmware supports the use of external camera triggers (cheap modules which are present in any selfie stick)? Or isn't this an option?

Edit: time per foto does not include the time for the movement and is just a delay after the external camera pin is set to the value high.
Release Time on the other hand defines the time, that the pin is kept on high. Depending on the camera model longer or shorter times might be required.
In the next firmware update, there will a third delay time, defining the time before the external pin is set to high.

[Michael-F-Ellis]

@OpenScanEu Thanks very much for the clarifications. The request for using a constantly timed trigger came from our user community. Some members want to use their personal smartphone cameras without having to sort out how to arrange a trigger connection. I suspected that the movement time was variable and, therefore, a potential source of errors - hence the inquiry.

I'll relay your comments to the group (not all of them are Github users).

The positioner we're building is scaled for objects not much larger than will fit in a cube 15cm on a side. We're intending to construct and attach a PiCam v2 (12 megapixel) as the default for capturing images. I'm sure there will be questions about whether the resolution is sufficient, depth of field, autofocus, lighting, background, etc.

Is it ok to ask those questions in this issue thread or should we create separate issues? Or is there a forum more suited those questions.

Thanks again for the detailed response and creating and maintaining the program!