Did Dew Cause This?

[bobro]

Below are small crops of 2 images : the lighter was taken earlier in the session and the darker later. Although a darker image would be expected if the sky became darker (which it may have done), the stars also darkened as DSS reported less stars in the darker image. The darker image looks a little less sharp and nebulosity was reduced in the full image.

There was heavy dew around and imaging was of the Soul nebula which was near the zenith, so some dew was able to form on the reflector scope mirror.

I haven't had this problem before (though targets were probably brighter) - was it the result of dew and if so (at the risk of going over old ground) what would be the best way to prevent it in future?

Thanks in advance.

[Delasaurus]

To my eye, looks like either you have a difference in exposure, or depending on the time of day you took them, a bit of light pollution.  My hunch is that it's light pollution as it was the first of your shots and the ambient light levels made the difference.

The first shot is also sharper than the second, so I suspect dew problems had built up by the time you took second image.

Light pollution my ol son...that's my view.

[geordie85]

I'd say it's down to your sky darkness levels. Of it was due I'd expect to see shine and dimness of your stars