Continued... Star Roundness Trial 1: New Fan ON....2nd repeat, different area of the sky Star Roundness Trial 2: New Fan OFF Star Roundness Trial 2: New Fan OFF......repeat, a different area of the sky Discussion: The Eccentricity figures are fairly well backed up by a visual observation of the stars. There is some evidence of field curvature and this is to be expected given that Celestron only guarantee star shape for an image circle diameter of 40mm, where the SBIG chip has a 52mm diagonal. With the new Fan ON, the average Eccentricity is in the range 0.51-0.58. This is a large improvement on the Eccentricity figures reported wth the old Fan, which were in the range 0.65 - 0.85 and were at the worse end of the scale in recent trials, suggesting a degradation of performance. The stars at the centre of the images where the Fan is ON show a small but perceptible amount of elongation. The Eccentricity for the Fan OFF trials were in the range 0.40 - 0.47. The stars at the centre of the images where the Fan is OFF are virtually perfectly round. Conclusion The previous fan arrangement , whether the fan itself and/or the vibration insulating foam, resulted in severe vibration causing substantial elongation of the stars in images captured with the SBIG 16803. Fan OFF trials showed this elongation was virtually completely eliminated. The new Fan and/ or insulating foam arrangement gives a substantially improved performance but it is by no means perfect and there is a demonstrable difference to the fan OFF images in terms of star roundness.