[daip] Overlapping Fields in IMAGR CLEAN

[landon at inaoep.mx]

Hello,

I have been experimenting with the use of multiple fields in AIPS's IMAGR. I
have found that running IMAGR with 2 fields, field one with boxes on the areas
where emission is expected, and field two with a box over the central 25% of my
512x512 pixel image, results in the best images (ie: most extended structure,
almost no artefacts, low noise). Both of my fields were set to size 0 (ie:
IMSIZE-10). As this is likely the procedure I will follow with all of our
cleaning of these observations, I need to understand better what AIPS is doing. 

>From what I understand from the AIPS manual, AIPS is simutaneously searching
both fields for components and then subtracting the componets at the end of each
major cycle. The clean box in field 2 full encompasses the clean boxes in field
one. Does this mean some areas are being "double cleaned"? The AIPS CookBook
also says "...never allow the search areas of one field to overlap with the
search areas of another field." However, this is exactly what I have done. Why
is it resulting in the best image I've been able to create thus far?

Thanks for you help in seeing into the guts of AIPS!
-Landon Halloran