Camera Calibration Source
I’m very excited to announce Technical Instruments’ first ever camera-specific calibration product! At left is an image of the CC-560, or Camera calibrator, which emits photons at 560nm.
All of the cameras in the microscopy world rely upon a single defining point that (theoretically) justifies the price premium we pay for them. That defining point is reproducible, quantitative linearity of intensity. Put simply, if I acquire some number of images, using the same camera settings, over a long period of time (days, weeks months etc), my camera should give me image intensities with the same brightness values, when provided the same amount of input light.
Note that linearity, as well as quantitative accuracy, are expected minimum specifications on camera info sheets. Some examples can be found here:
How does this quantitative/linear capability translate into real-world data for the end user? With difficulty! Upon purchasing a new camera, most new owners of a quality camera will find a unique set of conversion tables for their serial number camera. These tables note in part the individual electron to ADU conversion rates for each A/D readout speed, and Gain setting. This data can be used to discover how many electrons the camera collected for a given image. For instance one could have a 3.05 e/adu conversion rate at 10Mhz, as well as a 2.54x gain setting. Using these conversions we would find that a reading of intensity in an image, say with a value in the image of 100, would convert to ((100/adu)/gain) or (100/3.05)/2.54 = 12.9 electrons collected. Note this basic calculation does not include bias offset, which is another value provided in each camera’s specification sheet. The take home point here is that each camera manufactured will have it’s own, unique, set of values. You can use these values to convert your ADU’s (Analog to Digital Units) which are what you see as intensities in your image, back into electrons collected on the camera. This is especially useful when comparing images collected between multiple gain settings, or where camera speeds were changed and a corresponding change in image intensities was noted.
For some people, these series of calculations and corrections, as well as others, may be a required, however tedious, fact of life. On the other hand there are a vast majority of researchers who want answers to simpler questions, such as:
- What is the comparative sensitivity difference between the camera I used to work with in the lab down the hall, and this new camera I am now using?
- How do changes to my camera, such as binning, really affect my data?
- What do the detailed controls do on my camera? (Such as changing “Clearing” settings, or Parallel Clock speeds and voltages)
Customers using EM-CCD cameras may have additional questions, such as:
- Is the EM Gain slider on my camera (specifically first and second generation EM-CCD Cameras) linear?
- Is my camera aging over time? (See Andor’s explanation of this issue here)
The simplest answer for these questions was to have the customer find some photo-stable light source, and use that light source on the microscope to find the answer. The tough part was actually finding a useful photo stable source! As an answer to these challenges, a few colleagues and I have created this product, available from my employer, Technical Instruments. This calibrator is designed to give people simple and direct answers to these types of intensity based questions, with a minimum of hassle or headache. The product will work on ANY C-Mount camera, and can be used either for dedicated-use calibrations (i.e. install – calibrate – remove) or can be placed in between the camera and the microscope in a permanent installation (See example image of Andor camera and Nikon Ti-E microscope with CC-560 installed at right). I’ll be posting more soon on what this product can be used for, however I’m certain there are numerous uses for this that we haven’t considered. Please take a look at our new CC-560 Camera Calibrator.
