Integrating a microscope, Camera and Electronic shutter

Question

This is an optical engineering question rather than anything else. So I beg for your patience.

I have an inverted microscope which we are trying to do some cancer research with to image cells.

Since this involves extended periods of imaging, we would like to integrate some OEM components in the following order.

Halogen light source on the microscope -> electronic shutter (TTL triggerable) -> specimen -> Objective -> DSLR camera.

We have all the components except the a) shutter and b) Camera. I am trying to do some background research on how I can make an informed decision regarding these purchases to integrate efficiently.

My main issue is this. The electronic shutter and the camera are from TWO different vendors. For e.g., Uniblitz for the shutter and Canon 6D (or a variant). I would need to capture an image on an average once every 10-15 minutes. The exposure time would be one minute. So what would need to happen is that the shutter is triggered by a TTL input signal causing the shutter to open and the light to come through. The shutter is the open for 1-2 minutes. The camera then clicks the picture with an exposure of 1 minute. The shutter then closes. My main trouble is coordinating this whole process. The camera needs to recognize the shutter is open and take a picture. Alternatively, I can set it up so that the opening times and clicking time overlaps according to a pre-determined schedule. That seems a bit crude of a solution.

But I was wondering if any of the experts on this forum have an elegant solution to this issue? We can spend a bit of money, but I am trying to do this on the cheap (for example, program an Arduino board to send the TTL signal to trigger the electronic shutter from a computer). I saw IR triggering described somewhere. I am basically trying to find some inspiration here.

In the name of science, thank you!

Answer 1

Using an Arduino or similar, you can trigger the external shutter or you could switch the light source with a relay. If the light source runs directly from mains, you should leave the latter part for an expert. So far it is unclear why you need that external shutter.

After you started the light for the specimen, the Arduino can start the exposure with the camera. You can use the external camera trigger of the camera for this. The camera should be set to bulb mode. That way you can control the exposure time with the Arduino. The cables for the external trigger come in various forms, depending on camera brand and type. Usually you need to make a contact between two wires to start the exposure and interrupt the contact to stop the exposure. Use an optocoupler, controlled by the Arduino, to switch the wires together. The different pinouts for the shutter release connectors of various cameras can be found here.

This way everything is controlled by one system and you don't need to sense whether the light is already active before you start the exposure. Repeating this procedure automatically every 10 to 15 minutes can also be controlled by the Arduino.

As you have a long exposure time, this will increase the noise of the image as the sensor get's warmer. I would recommend getting a camera which features dark frame substraction. After a camera with this feature finished a long exposure it will take another exposure of same exposure length with it's internal shutter closed. The noise found in this dark frame is then substracted from the actual image, improving image quality.

Answer 2

A light-activated in-line switch could: 1. prevent the event sequence until the subject is illuminated; 2. ensure that the subject is illuminated.

Answer 3

A few thoughts:

1. Rather than trying to integrate a DSLR's software interface, trigger the camera's shutter with a mechanical actuator -- actuating a remote shutter release is probably preferable to the shutter button directly. A mechanical system will be straight forward physics applied to a mechanical system in lieu of trying to understand the complexities of software interfaces and taking dependencies on operating systems and many millions of lines of code.

2. One and two minute exposures are likely to have noticeable thermal/dark/sensor noise. This can be mitigated in software. Avoiding much of it during image capture might be preferable.

3. Slightly more specialized cameras used for astrophotograhy and similar applications are actively cooled to boost signal to noise rations.

4. A DSLR might not be the best instrument for this application. Thumbwheels, buttons, and a through the lens viewfinder don't seem to add much relevant capability. Were it me, I'd compare the Canon options to a something from ZWO and similar vendors. ZWO also provides an SDK and Linux support making control via Raspberry Pi a possibility (not much more cost than an Arduino).

To me, the engineering problem is as much about choosing instruments based on their interfaces as anything else because development time can easily swamp hardware costs.

Answer 4

It may be worth looking at some if the cheap intervalometers on ebay as a cheap source for a camera trigger cable - some use a stereo jack plug to connect to the camera connector lead (so the same basic device can be connected to different cameras). The camera interface usually uses one contact for AF and one for shutter release - so since you probably don't need AF, you could use a relay to trigger the camera shutter = then you could use the arduino to control both the camera (via a suitable relay) and your electronic shutter.