Dew affecting guiding?

[nigelbeaumont]

Just finished an evening of narrowband imaging of the Crescent Nebula using an MGEN to guide - looking through the images, I've noticed that the guiding is OK for the first hour or so, but the later images begin to show signs of star trailing (all the subs have the same duration). Any idea whether dew would cause this effect? I was using dew heaters for the first time on both the imaging and guiding scope, but looking at the main scope objective, there was still a little dew on one edge (forgot to check the guider). What might be other causes, could heat from the dew tape create a pocket of warm air in the dew shield that would affect the guider seeing?

[ChrisLX200]

No, I don't think that would affect it. But if you were imaging the Crescent then later on it would have moved well into the West and the scope/guider may have flexed somewhere as the weight shifted. What were you using to image with - refractor or 200PDS?

ChrisH

[nigelbeaumont]

I was using the refractor

[cjdawson]

Stating the obvious - did your guider dew up?  If so, it'll have not been able to see.  Just a thought.