Sorry, not right on topic but related in terms of resolution. I don't understand this. This is from the Astrophysics site re the BARADV barlow used on the AP175. I always thought that theoretical resolution is determined by aperture and that this is rarely if ever achieved due to seeing. Yet here it seems that going from f7 to f14 there is an increase in resolution.
From the site:
"These two images compare the resolution with and without the Advanced Convertible Barlow using a QSI 683 (5.4 micron pixels) camera with the AP 175EDF at 1400 mm focal length. The left image is shown at 400% screen size and the right image with the Barlow is at 200% screen size, keeping the two images equal in perspective
"
George (of AP) commented in a discussion on the TEC discussion group that he believed that pix size was a factor here where at f7 perhaps the pix are too large to permit enlargement to match image size at f14. If true then a longer focal length would have the potential to increase resolution. I don't know what to think! I do know that 4 years ago I took a pretty high resolution photo of M83 using this barlow on my TEC140. I'm curious what you all think about this.
Peter
M83:
http://www.pbase.com/prejto/image/151603452