Is this caused by Dew

[Scooot]

I was trying out my new Asi 2600 and EQ 35-M last night and I have some big halos around the bright stars. I think they're over exposed as I can see them in the linear image, but even so, the halos look odd. I wondered whether it is the effect of dew.

This is a single 5 minute sub at 100 gain controlled with the Asiair on my Tak FS60CB with flattener. Asiair calculated the focal length as 375MM. I've just done an STF stretch on the image to show the halos but nothing else. In addition, the star shapes on the edges are off, so I wonder whether my back focus is slightly out, and if so, is it possible to determine from the distortion whether I'm short or long back focus. I've set it up at 56mm using a baader varilock spacer.

Thanks for any help.

Edited January 31, 2021 by Scooot

[Shimonu]

Do you use any dew heaters and do you remember what it was like during the session? I'm no expert but dew seems pretty possible.

[Scooot]

45 minutes ago, Shimonu said:

Do you use any dew heaters and do you remember what it was like during the session? I'm no expert but dew seems pretty possible.

Hi, thanks for the reply. I used the dew heater on the sensor but not on the telescope tube, although it does have a dew shield. I’ve never really had much of a dew problem with the little tak before but it was pointing almost vertical. I also wondered whether it was a reflection from the bright moon but as it seems to be around all the bright stars I thought that was unlikely.