I want to use a digital camera to capture slow changes of an object for scientific purposes, subject to the following constraints:
- The camera is a Canon EOS Rebel T5i.
- The position of the object, camera, and lighting are fixed. Changes in lighting are negligible.
- The object is about 20 cm from the camera.
- My main interest is to capture small changes in brightness or colour of the light diffracted by the object by comparing subsequent pictures.
- My secondary interest are details of the object’s surface or where the above changes happen, respectively.
- I do not need to normalise photographs for comparison to references or similar. I only need to compare between photographs taken with the same camera.
- Changes of the object happen on a timescale of roughly an hour.
Note that this is not for purposes of scientific illustration, but to gather scientific data. I essentially abuse the camera as a photon counter.
What I did so far
- Use the raw CR2 format from the camera since it has a higher intensity resolution (about 14 bit) than any RGB-based formats (8 bit).
- Disable all automatisms to avoid them getting in the way of comparing pictures.
- Set the focus using autofocus on one exemplary object. Then switch to manual focus to freeze it.
- Use the largest aperture (F2.8) for maximum sharpness.
- Set ISO to 100 (the camera’s lowest native ISO) to reduce noise.
- Set the exposure time to the highest value for which the raw data is not capped (except maybe for a few pixels).
- Ignore other settings such as white balance, as they do not affect the raw data (but are applied in digital postprocessing).
Is this approach reasonable or am I missing something?
My biggest concern is that the resulting exposure time is about ⅛ s, which does not use the full potential of what the context of the scientific experiment allows for, which would easily be 10 s of exposure time.
I know that I could technically combine data from several pictures, but this would be very tedious.