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Hi Doug,
Why would this be so? I can't think of a good reason why filtering out all the spectrum except a narrow band in the red region is better than a wider band also in the red region?
It's not the overall size I was trying to point out, it's the sampling. The red stars are blocky, i.e. not as well sampled as the Ha stars, which show a nice curve to them. The images weren't taken on the same night, so the seeing conditions may not have been the same. The nebulosity doesn't seem to be affected by the sampling at all, so I suppose if you're only interested in diffuse objects then the sampling rate doesn't matter that much?
FYI according to CCDStack the FWHM of the red image stars is 3.1 - 3.3, the Ha is 3.4 - 3.6, depending on the star involved.
Grab the images and blow them up a bit (but don't resample them), you'll see what I mean.
Cheers
Stuart
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