Peter
I had a quick skim of the article. I was distracted by the fact that you mentioned specifically stellar limiting magnitude. So it seems it matters not to the CCD that the physical image at the focal plane will be 2.5X brighter in the F5. I am a bit of planetary nebulae nut and its been my closet dream to make a photographic catalogue of far southern planetaries. I guess this means with a CCD I can shoot at F16 with no loss of speed over an F4, which makes my project all the more attractive.
Regards collimation: I would have been very nervous about purchasing a budget telescope with highly aspheric surfaces where you couldn't collimate the primary element but your findings allay my fears.
I don't really see the difference in difficulty of collimating a small Newtonian against a SCT or GSO RC. The secondary you don't routinely touch after it has been aligned, and at F5 a common or garden laser collimator gets you close enough. At F4 to F4.5 a squizz at high power at a defocused star tells you which primary collimation knob to move just as you would do to tweak the secondary on an SCT or RC.
[QUOTE=Peter Ward;490652]Mark,
1) I was incorrect in quoting Russ as the author of the F-ratio myth...it was in fact Stan Moore. Interested punters can read about it here:
http://www.stanmooreastro.com/f_ratio_myth.htm
Do you disagree with Stan's analysis?
2) You are assuming the primary is decentered by the factory. I've tested close to a dozen of these scopes are not one had a problem. Also last time I checked an F5 of anything was far more of a bugger to collimate than a F8