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.png c0.0020_n0200.10000.resid.png

niter=1 000 000:
c0.0020_n0200.1000000.png c0.0020_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.png c0.0010_n0400.5000.resid.png

c0.0010_n0400.6000.png c0.0010_n0400.6000.resid.png

c0.0010_n0400.7000.png c0.0010_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.png c0.0005_n0800.100.resid.png

c0.0005_n0800.500.png c0.0005_n0800.500.resid.png

c0.0005_n0800.1000.png c0.0005_n0800.1000.resid.png

c0.0005_n0800.2000.png c0.0005_n0800.2000.resid.png
Topic attachments
I Attachment Action Size Date Who Comment
c0.0005_n0800.100.pngpng c0.0005_n0800.100.png manage 51.5 K 2010-03-14 - 21:28 RemyIndebetouw  
c0.0005_n0800.100.resid.pngpng c0.0005_n0800.100.resid.png manage 77.5 K 2010-03-14 - 21:29 RemyIndebetouw  
c0.0005_n0800.1000.pngpng c0.0005_n0800.1000.png manage 44.7 K 2010-03-14 - 21:31 RemyIndebetouw  
c0.0005_n0800.1000.resid.pngpng c0.0005_n0800.1000.resid.png manage 85.0 K 2010-03-14 - 21:32 RemyIndebetouw  
c0.0005_n0800.2000.pngpng c0.0005_n0800.2000.png manage 70.6 K 2010-03-14 - 21:38 RemyIndebetouw  
c0.0005_n0800.2000.resid.pngpng c0.0005_n0800.2000.resid.png manage 126.5 K 2010-03-14 - 21:39 RemyIndebetouw  
c0.0005_n0800.500.pngpng c0.0005_n0800.500.png manage 48.0 K 2010-03-14 - 21:26 RemyIndebetouw  
c0.0005_n0800.500.resid.pngpng c0.0005_n0800.500.resid.png manage 91.5 K 2010-03-14 - 21:28 RemyIndebetouw  
c0.0010_n0400.5000.pngpng c0.0010_n0400.5000.png manage 25.1 K 2010-03-14 - 21:12 RemyIndebetouw  
c0.0010_n0400.5000.resid.pngpng c0.0010_n0400.5000.resid.png manage 49.5 K 2010-03-14 - 21:13 RemyIndebetouw  
c0.0010_n0400.6000.pngpng c0.0010_n0400.6000.png manage 26.9 K 2010-03-14 - 21:14 RemyIndebetouw  
c0.0010_n0400.6000.resid.pngpng c0.0010_n0400.6000.resid.png manage 55.3 K 2010-03-14 - 21:15 RemyIndebetouw  
c0.0010_n0400.7000.pngpng c0.0010_n0400.7000.png manage 48.0 K 2010-03-14 - 21:16 RemyIndebetouw  
c0.0010_n0400.7000.resid.pngpng c0.0010_n0400.7000.resid.png manage 93.4 K 2010-03-14 - 21:17 RemyIndebetouw  
c0.0020_n0200.10000.pngpng c0.0020_n0200.10000.png manage 15.7 K 2010-03-14 - 20:55 RemyIndebetouw  
c0.0020_n0200.10000.resid.pngpng c0.0020_n0200.10000.resid.png manage 17.5 K 2010-03-14 - 21:11 RemyIndebetouw  
c0.0020_n0200.1000000.pngpng c0.0020_n0200.1000000.png manage 12.8 K 2010-03-14 - 21:04 RemyIndebetouw  
c0.0020_n0200.1000000.resid.pngpng c0.0020_n0200.1000000.resid.png manage 12.8 K 2010-03-14 - 21:07 RemyIndebetouw  
Topic revision: r3 - 2010-03-15, RemyIndebetouw

This site is powered by FoswikiCopyright © by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
Ideas, requests, problems regarding NRAO Public Wiki? Send feedback