Red channel and low declinations

[kirkster501]

Hi all, I ran my imaging rig on a few globulars in Ophiuchus the other night (M10, M12 and M14).  Just 10 x 180 seconds in each of R,G,B on all three of the clusters so as to get something in the bag this time of year of almost zero imaging time. 

I used my Atik460 on the TEC140 with field flattener and Astrodon filters.  Autofocus running.  Blue and green channels 100% bang on.  To my surprise the red channel is not as good.  Just about usable but definitely not as good as the B and G and slightly "blobbier".  I am surprised at this - I would expect the blue to be more effected by the lower declination.  I am using an IR Block filter in front of the whole imaging train in the nosepiece in front of the filter wheel and therefore IR pollution - not that there is any in that direction anyway - should not be an issue either.  I can share some subs later.

Given, it is not the best time of year for imaging, it never got 100% dark, I am imaging these objects not far above some neighbouring houses (rising heat from the day radiating off the roofs and affecting the red more maybe?) and they are lowish objects (although not unduly so) but still, I thought a bit odd, especially since the B and G are perfect.

Any thoughts please guys?

Thanks, Steve

[ollypenrice]

It is a bit odd for the reasons you suggest.  Could it simply arise from a change in local conditions? The seeing going off during the red sequence? (This assumes you did each colour in a block rather than scrolling RGB,RGB etc.)

Olly