Clean appears to be unstable when the pixel is smaller than about 0.1 of the synthesized psf fwhm.
The following data has synthesized beam ~0.015arcsec, rms of the visibilities =0.004, rms of a "well" cleaned image ~1.5e-7 Jy/bm off-source.
I tried a series at fixed angular image size - cell size decreasing and imsize increasing accordingly. When cell<~beam/7, I can clean very deeply (arguably too deep, but that's not the point here - the point is that I should be able to clean to a couple of sigma, and even overclean, without it going completely haywire in the space of a few iterations). All images are from -1e-4 to 8e-4, and all residuals are from -1e-5 to 1e-4

cell=0.002" = beam/7.5
threshold = .0003mJy
this goes down to an rms off-source of 1e-7, and continued cleaning, while maybe not optimal, doesn't make it go crazy.

niter=10 000:
c0.0020 n0200.10000.pngc0.0020 n0200.10000.resid.png

niter=1 000 000:
c0.0020 n0200.1000000.pngc0.0020 n0200.1000000.resid.png

cell=0.001: we can get down to a few e-6, which is reasonable, but pushing it a little goes foobar fast:
c0.0010 n0400.5000.pngc0.0010 n0400.5000.resid.png

c0.0010 n0400.6000.pngc0.0010 n0400.6000.resid.png

c0.0010 n0400.7000.pngc0.0010 n0400.7000.resid.png

with cell=0.0005, we can barely get down to 1e-5 before things to nuts, and there's never a good image with the right amount of flux. in fact, the flux even after a few iterations is twice what it should be...

c0.0005 n0800.100.pngc0.0005 n0800.100.resid.png

c0.0005 n0800.500.pngc0.0005 n0800.500.resid.png

c0.0005 n0800.1000.pngc0.0005 n0800.1000.resid.png

c0.0005 n0800.2000.pngc0.0005 n0800.2000.resid.png
Topic attachments
ISorted ascending Attachment Action Size Date Who Comment
c0.0005_n0800.100.pngpng c0.0005_n0800.100.png manage 51 K 2010-03-14 - 21:28 RemyIndebetouw  
c0.0005_n0800.100.resid.pngpng c0.0005_n0800.100.resid.png manage 77 K 2010-03-14 - 21:29 RemyIndebetouw  
c0.0005_n0800.1000.pngpng c0.0005_n0800.1000.png manage 44 K 2010-03-14 - 21:31 RemyIndebetouw  
c0.0005_n0800.1000.resid.pngpng c0.0005_n0800.1000.resid.png manage 85 K 2010-03-14 - 21:32 RemyIndebetouw  
c0.0005_n0800.2000.pngpng c0.0005_n0800.2000.png manage 70 K 2010-03-14 - 21:38 RemyIndebetouw  
c0.0005_n0800.2000.resid.pngpng c0.0005_n0800.2000.resid.png manage 126 K 2010-03-14 - 21:39 RemyIndebetouw  
c0.0005_n0800.500.pngpng c0.0005_n0800.500.png manage 47 K 2010-03-14 - 21:26 RemyIndebetouw  
c0.0005_n0800.500.resid.pngpng c0.0005_n0800.500.resid.png manage 91 K 2010-03-14 - 21:28 RemyIndebetouw  
c0.0010_n0400.5000.pngpng c0.0010_n0400.5000.png manage 25 K 2010-03-14 - 21:12 RemyIndebetouw  
c0.0010_n0400.5000.resid.pngpng c0.0010_n0400.5000.resid.png manage 49 K 2010-03-14 - 21:13 RemyIndebetouw  
c0.0010_n0400.6000.pngpng c0.0010_n0400.6000.png manage 26 K 2010-03-14 - 21:14 RemyIndebetouw  
c0.0010_n0400.6000.resid.pngpng c0.0010_n0400.6000.resid.png manage 55 K 2010-03-14 - 21:15 RemyIndebetouw  
c0.0010_n0400.7000.pngpng c0.0010_n0400.7000.png manage 47 K 2010-03-14 - 21:16 RemyIndebetouw  
c0.0010_n0400.7000.resid.pngpng c0.0010_n0400.7000.resid.png manage 93 K 2010-03-14 - 21:17 RemyIndebetouw  
c0.0020_n0200.10000.pngpng c0.0020_n0200.10000.png manage 15 K 2010-03-14 - 20:55 RemyIndebetouw  
c0.0020_n0200.10000.resid.pngpng c0.0020_n0200.10000.resid.png manage 17 K 2010-03-14 - 21:11 RemyIndebetouw  
c0.0020_n0200.1000000.pngpng c0.0020_n0200.1000000.png manage 12 K 2010-03-14 - 21:04 RemyIndebetouw  
c0.0020_n0200.1000000.resid.pngpng c0.0020_n0200.1000000.resid.png manage 12 K 2010-03-14 - 21:07 RemyIndebetouw  
Topic revision: r3 - 2010-03-15, RemyIndebetouw
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