Quote:Aperture and focal ratio should be factors in such a decision. Smaller aperture and/or slower focal ratio will be more forgiving in regards to CA (in general).
Quote:Aperture and focal ratio should be factors in such a decision. Smaller aperture and/or slower focal ratio will be more forgiving in regards to CA (in general).You'll have to narrow down your desired aperture range because some folks might spend $3K or more for an apochromatic finderscope.
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Quote:I'm curious, why would one spend upwards of 1 to 3k for a triplet apo if a doublet apo, there are a couple of awesome ones out there, with zero CA were available?What advantage if any would a triplet offer? I know the doublet would cool a lot faster, so that's not working in the triplet's favor... anyone care to chime in?
Quote:an Arcturus star test to compare on both scopes are posted here: http://www.flickr.com/photos/70224675@N06/
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Quote:And this sample done with the Orion ED80 Triplet. spikes were done with Starspike pro on Photoshop
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Quote:more glass you put in the path the dimmer the view, unless somehow the lens is amplifying the light
Quote: Again, unnecessary for all colors to come to the exact same focus for visual use, but the long exposure astro-camera sees things that our eyes can't see.
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Quote: but I have to disagree with the above statement.
Quote:I believe that the OP is trying to determine if it is essential to have a triplet for visual use, and my own belief is that the advantage is only important for larger, fast refractors used for imaging.
Quote:For visual use, a 4" ED triplet will show you pretty much everthing that a 4" f/9 ED scope will show you.
Quote: Summary: Apochromatic doublets are few and far between.... Apo = triplet
Quote:...A 4 inch F/9 probably has quite acceptable color correction for most observers but it's also about 3 feet long. A 4 inch F/6 or even F/7 is about 2 feet long, is handier to use, requires less substantial mount and may even be airline portable.
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Quote: I said that it was unnecessary to have a triplet to get good visual performance.
Quote: The amount of fringing on modern ED refractors is so small that it will likley only be noticed on bright stars.
Quote:But if the goal is to see all of the detail in all of the targets one points the telescope at, a triplet is not really necessary.And if one wants completly color free images, one can buy a reflector.
Quote: But for visual use, I stand by my belief that unless the system is very large and very fast, for visual use, there is no more detail to see using a triplet than an ED doublet.