FWHM & humidity. Correlation?

[georgeroush]

Last night, here in Southern Connecticut, SharpCap refused to livestack because the FWHM was too high... around 5.0 with all red bars. I used a bahtinov mask for optimal focus and further tweeked the focus so that I got the lowest possible FWHM.

I use the hyperstar with my celestron scope so I was wondering whether the problem was with hyperstar. I ruled this out by attempting to livestack without hyperstar and just using my ZWOASI2600 MC Pro camera; the FWHM values were even higher.

Last night was also humid with condensation on all cooler objects (I used a dew shield). I did manage to livestack a couple of weeks ago when it was not humid. When I got up this morning the humidity was 64%.

Is my problem due to high humidity? Is there any way around this problem? Only image on low humidity nights? Image only in low humidity regions such as Arizona?

Best wishes... George

[admin]

Hi George,

it sounds like you have probably turned on the FWHM filter functionality in live stacking to only allow the better frames (lower FWHM) into the stack. You can either turn up the FWHM threshold or turn this functionality off to get stacking to happen even in poor conditions. See https://docs.sharpcap.co.uk/4.0/#Filter%20(FWHM)%20Tab for more info.

cheers,

Robin

[georgeroush]

Yes, that worked! Thank you!

I now have a new problem ... not seeing sufficient stars. I've had this problem before but it corrected itself in some way I don't understand, and I was then able to easily polar align. There must be a setting which has changed automatically. I've turned up the gain to maximum and turned up the sensitivity to 94%. The histogram still shows a low level.

What else can I do to detect stars?

[admin]

Hi George,

in the 'Alignment' section for live stacking you can turn on the 'optimize for faint stars' checkbox, which might help. Also make sure the noise reduction setting is not turned up too much (0.5 to 1.5 should be fine). If you are still having problems then taking longer exposures or a higher gain might help.

cheers,

Robin

[georgeroush]

OK.. Thanks, Robin. LM give this a try tonight.
George