CCD Bahtinov Focussing Problem. This is driving me mad!

[bendiddley]

Ok so I went out last night to carry on sorting the last teething issue I’ve got with my Starlight Xpress SXVF-M25C which I have finally sorted, however... I now have again a blurry rendering of the spikes on the bahtinov mask which when I went out last time I had sorted. Last time I fixed the blurry spikes issue by increasing the exposure time in live view to 7 seconds (I’m using Astro photography tool by the way) and I got some lovely clear, crisp spikes. However this time for some reason the spikes were all blurry again. I’m wondering whether it was the seeing conditions that made it like that as I had not changed any settings since the previous time? I tried experimenting with bin settings and found the rendering of the spikes was better using 1x1 but not enough to distinguish them (see first photo). If I tried with 2x2, 3x3 or 4x4 the spikes were completely unrecognisable (see second photo), just a blurry blob. As said no other settings had been changed since my last session other than me experimenting with the bin settings. I also tried experimenting with the live view exposure time going up to 15 seconds at one point and as low as 1 second but nothing seemed to work, it was marginally better at around the 7 second mark. What’s going on?? I’ve attached a photo of the spikes using bin 1x1 at 7 seconds.
 

[knobby]

I never have much luck with live view, I generally take a 5 second image then view it, tweak and try again.

Must admit it's weird that it works one night then not another ...

[michael8554]

If that was the best focus you could achieve I would suspect dew. 

Each increase in Binning will reduce the resolution, making the result look even fuzzier. 

Michael 

[bendiddley]

2 minutes ago, michael8554 said:

If that was the best focus you could achieve I would suspect dew.

Each increase in Binning will reduce the resolution, making the result look even fuzzier.

Michael

Thanks but there was no dew. 

[bendiddley]

8 hours ago, knobby said:

I never have much luck with live view, I generally take a 5 second image then view it, tweak and try again.

Must admit it's weird that it works one night then not another ...

Thanks for this, your method might be the only option. Yeah it is a bit weird that it worked the last time but not this.

[michael8554]

Isn't this a cooled camera?

Then frost, or maybe still dew, or condensation....... 

Michael 

[bendiddley]

15 hours ago, michael8554 said:

Isn't this a cooled camera?

Then frost, or maybe still dew, or condensation.......

Michael

This is a very interesting point. I hadn't even thought it might be condensation or frost. It was a much colder night this time than when I took it out previously, so it could well be this. Does the condensation form on the glass window or the chip? I will have to take it out and test on the next cold evening. Any suggestions for how I can remedy this?