<https://stargazerslounge.com/topic/82057-low-profile-focuser/#comment-800790>
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"Depends on what you mean by \"contrast\". It does make some low contrast planetary features a tad less visible (notably on Mars, Jupiter and the subtle colour and luminance variations in the Moon maria), but to be frank, even 25% isn't that large a central obstruction. It also does not affect small high contrast features that much. See Thierry Legault - What are the effects of obstruction ? for a discussion. You have to note that on larger scopes it's even less important for most mortals (who don't live in Florida or Barbados), as on a 12\" you'll need to be working at around 400x before you'll really be able to see the difference oh so slightly. And for that to happen, you have other more important gremlins to fight first: collimation and cooling. Also, it's possible to be penny wise but pound foolish: if you get a small sized secondary, it has to be an excellent one (Protostar, Antares Optics, NY --not Antares Optical-- or Orion Optics), because if you use a cheap one and its edge is so-so you're going to lose more than you gain by having a central obstruction that is 3% smaller : on a large secondary you won't be using the edge at high power, on a really small secondary you'll be using the edge even pretty close to the axis. For deep-sky observation the central obstruction is almost completely irrelevant; it's much more important for your scope to be well baffled (and to have a Paracorr if you want to use the whole field and want pinpoint stars). Personally? I'd get a 2.4\" secondary and a lower profile focuser if you're going to be looking only at planets, a 2.6\" secondary and a lower profile focuser if you are going to look at planets for a considerable fraction of the time, and a 3.1\" secondary if it's mainly a deep sky scope with the odd planet thrown in (they are still going to be breathtakingly detailed if the seeing cooperates; 12\" is a lot of aperture unless you're blessed with extremely good seeing all of the time!) \n"
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