This manual covers the setup and usage of the two external shutters made by Michiel van Noort. The main mechanical component is a chopper wheel, hence they are often called the "choppers". The choppers work for Megaplus cameras of the first generation (camera + external controller box) and second generation (camera with computer cable directly to it). They do not work for the third generation "Megaplus II" cameras.
The choppers are supported "as is", i.e. if you think you can make them work, use them. Use this manual as a guide but it's probably easier to make it work if you've had them demonstrated to you before.
The choppers come with electronics that intercept the control signals from the camera computers and make sure that the cameras are synchronized to each other and to the chopper wheel.
The sketch to the right illustrates the use for a broadband Phase Diversity setup for the SOUP filter. The shutter synchronizes all three cameras (marked "1.6"). This setup allows PD processing of the broadband images and subsequent deconvolution of the images from the SOUP camera - or joint processing of images from all three cameras (Multi-Object Multi-Frame Blind Deconvolution).
The following photos show the parts of the chopper setup and how they are connected.
Put the chopper wheel in the beam somewhere before the beam-splitters that separate the beams to the individual cameras that should be synchronized. Make sure the interesting part of the FOV is not vignetted when the shutter is open.
The image to the right shows a blue-beam setup where the chopper controls five cameras in a tight configuration with several beam-splitters. The light enters from top, through the black chopper, parallel to the naked optical rail.
A thin black cable from a 5V adapter goes in the hole on the side of the gray box attached to the chopper wheel. At least one of the lights on that box should light up if these two cables are correctly connected.
A black cable connects the shutter speed control box (in the observing room), via a gray extension, to the chopper (connector at the bottom). If this cable is correctly connected, the chopper should start turning when the power of the control box is switched on and the speed dial is set to a nonzero speed (which unfortunately can not be seen, but turn the knob if there is no response). The cables from the control box are labeled with 1-1 serial cable and a green color ring (for cable 1) and yellow color (for cable 2 ).
Then connect the cameras to the shutter. This is done by inserting a black camera electronics box between the camera interface cable and its connector, see image to the right. Be careful with the female SCSI plugs, as some of them are actually not or very weakly mechanically attached to the cables, so always pull the plug and not the cable.
NOTE: If possible, do the focus of the cameras BEFORE you connect the camera boxes (see below). This avoid that users are plug in and out several times the very delicate connector of the black box to the camera.
NOTE: Symptoms of broken connectors: if some of the wires are not connected inside the SCSI plugs, you can expect strange things in the images that look like noise or stripes, especially if you get close to saturating the cameras. If you suspect that is the case, the only things you can do are trying to fix the plug or find another camera box.
The camera boxes connect via the gray daisy chain cables to one of the connectors on the gray box on the chopper, possibly via other camera boxes, see photo above. Several camera boxes connected in series and to one connector on the chopper form a chain. All cameras on a chain are completely synchronized. If you have cameras that you want to run at a slower pace (i.e. synced with the fastest camera but does not take every frame) you need to put those cameras on a separate chain. The slower chain then needs to be switched off on the gray box on the chopper. All cameras (regardless of chain switch-status) will wait for the cameras on the switched-on chains but not for the ones on the switched-off chains.
There are two plugs on each camera box. The one next to the LEDs should be attached to the gray box or the connector opposite the LEDs on another camera box. If you do this wrong nothing should break, but nothing will work either. See images.
The switches on the gray box will force cameras on chains in the corresponding connector sockets to wait for each other when they are switched on (up) and will ignore the state of the chains attached to connector sockets for which the corresponding switch is switched off (down). The leftmost switch is for the bottom connector, the rightmost for the top connector, etc... If a connector on the gray box on the chopper is not used, the switch position should be set to off.
Try it first with one camera and then add more once the first one works.
NOTE: There are 2 "special" camera boxes: one with a switch that switches off the box and allows the camera to be triggered directly by the observing computer without removing the box, this was done for SOUP calibration because it needs to be done so often and that is not so good for the connectors on the box and the camera. The other "special" box has a COAX cable running out of it, so that it can be used with the Uniblitz external shutters. This cable needs to be attached to the "pulse" input (not sure about the name of the input here, but it was NOT the trigger input) of the Uniblitz shutter control box, so that you can still use the 4.2 camera with the broken shutter if you absolutely have to.
The exposure time is 1/(6X), where X is the measured speed of the wheel in Hz as reported on the control box. There is a Hz/sec conversion table attached to the speed control box. Change the exposure time by operating the knob that changes the wheel speed. Change slowly and gradually to give the wheel time to speed up or down.
Not very stable exposure times at low frequencies makes it difficult (but not impossible) to focus cameras using the choppers. Solution if you can't make it work: Turn chopper off, turn the wheel so it's open. Disconnect the camera box and use internal shutters for focusing. (For the "special" box with a switch: Use the switch to do the bypass.)sa
NOTE: Avoid repeated disconnecting/connecting if possible. If necessary, use a small screw driver and pull out alternating the connector edge, little by little the connector from the camera. Before you connect the cable check all the male pins so no one is bent or left inside the connector chassis. Ask Rolf for help.