Mr B thanks for that
the further test as mentioned above showed an increase in the noise level the longer the camera was left on, the first image taken after the Peltier had been left on for half an hour and the camera off shows minimal noise but as the CCD heats up while the camera takes exposures 3 minutes apart the noise level rises between each image.
The best thing would be to turn camera off for a few minutes between each image which unfortunately is not practical except if long exposures are being taken.
Each of these images is the same ISO etc as previously mentioned although the time between frames is reduced.
From this it seems that the Peltier cold plate does make a difference depending on how it is applied.
Although another issue may be that the Pentax ccd has a higher noise to signal ratio than other camera's.
