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Message: <blockquote data-quote="henry link" data-source="post: 1420681" data-attributes="member: 6806">Frank,Just try the eyepiece. A 25mm eyepiece is the equivalent of a 10x loupe. You might need to use it backwards to get it close enough to the scope eyepiece and be careful to keep it centered. Longitudinal CA in a scope with a conventional crown and flint objective varies almost entirely with objective size and focal ratio, so what you see in this scope is similar to any other achromatic scope of the same size and focal ratio (even the Swarovski 80mm non-HD would be no improvement). An 80mm achromatic objective with a focal ratio below f/6 has plenty of CA. The question is what is the "true" size of this objective. The more the objective is stopped down the more CA will be improved.Now let me climb on my soap box for a bit. I'm sure you've read some of my complaints about reviews of scopes that don't actually test the optics, like the Campfire reviews of the Promaster scope. It's more possible to get by with reviewing binoculars that way because they are never pushed to the optical limit. Scopes are different. The same optical defects that would be insignificant at binocular magnification can seriously compromise the view at scope magnifications, so I think it's essential to learn how to do a few basic optical tests if you want to review scopes. The very first thing should be a high magnification star test. Without that you just can't tell what defects are present in the specimen you're reviewing. That's where the Campfire reviews (and many others) have gone off the rails. Reading between the lines it's probable that they were reviewing a defective scope without knowing it. Most disagreements about the quality of a particular scope probably arise from undetected sample defects. One person is reporting the performance of a cherry vs someone else's lemon. By itself, a star test will tell you almost everything about the quality of the axial image. Color bias, light transmission and off-axis performance are separate issues. The USAF Test Pattern  will allow you to establish how close a scope approaches diffraction limited resolution (a number that's a pretty good short hand indicator of axial performance), but it's limitation is that it can't reveal why a scope performs as it does. I know most people consider this kind of testing to be a pain in the rear, but since you already spend lots of time looking through optics I hope you'll consider joining the few of us optigeeks who try to do more careful and thorough testing.Henry</blockquote>

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