Optical Imaging


Stability

Questions:

Often I see a pattern noise which is kind of circular or does not have any particular geometric shape. Why?
or
Often I see that the histogram of the enhanced image is moving to the left and then back to the right and over and over again. Why?
or
Often I see that the gain is very not stable and the standard deviation of the gain calculation is relatively high (>0.4). Why?
Answer:

Very often all those questions are related to mechanical stability of the camera relative to the target, or to the stability of the DC illumination.

Mechanical instability may be due to:

  1. A floating table is not floating due to lack of air, or not floating due to tight cables between the table and floor.
  2. Camera holder is not secure.
  3. Target is not secure.
  4. Light guide are not secure.
  5. Large movements of the Cortex due to respiration.

Illumination instability may be due to :
  1. Old bulb. Just replace it.
  2. Oxidized contacts in the Zeiss lamp housing socket. Take the bulb out and clean the two contacts (holes) with a proper size small drill bit or with a watch maker small screw driver. Put in a new bulb.
  3. Poor connection of the lamp cable to the power supply. Tighten the contacts as hard as you can. (if this is a new installation, check to see if the cables that connect the power supply and the lamp are thick enough).
  4. Bad connections on the power cables, if it was extended. Double check.
  5. Poor connection of the lamp cable to the socket. Open and inspect if 1-4 fail to improve.
  6. Poor DC stability or high AC ripple on the power supply, Replace the power supply or at least try to connect the sense terminals as close to the lamp as possible.
    In order to check DC power stability, Use a digital volt meter and watch for several minutes to see if there is any short term drift, then check hourly for a few hours, looking for long term drift. (Make sure DVM has a new battery). If possible, it would be better to use an oscilloscope set to measure AC voltage at low voltage per division (50mV/Div.) and watch for the ripple frequency and pick to pick voltage.
    In order to check light stability a digital light meter might be used. If you do not have one, please contact OI and we would arrange for you to borrow one for this purpose.


Optical Imaging