APO vs. ACHRO

Wikipidea (the place I go to find out what all these words mean) seems to insinuate that an APO would be required for CCD imaging, but not neccesary for visual observation. Is this correct? Can you really see the difference with your own eyes?

Darryl

Yes you will see it, specially if you point it at a very bright object, like The Moon or the planets...

Longer focal length ACHROS will show much lower color aberration than the shorter focal length ones... (like comparing an f/15 versus an f/5, the f/15 will show almost NO false color, while the f/5 will most likely show quite a bit of it)

APOs are designed to show NO false color...


Clear skies! 8)

Darryl,

Check out the two photos in this thread and see for yourself what the difference looks like.

http://www.astromart.com/forums/viewpost.asp?forum_post_id=425706&poll_id=&news_id=&page=

clear skies,
dan

. Is this correct? Can you really see the difference with your own eyes?

Darryl
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As others have said, you can see the difference with your own eyes. Bright targets like the planets will show a purple haze around them. This is the result of the fact that different colors come to focus at different points with an Achromatic lens. This is normally termed "chromatic aberration" or "false color."

It is a function of both focal ratio and aperture. It increases with Aperture and decreases with longer focala ratios. Thus an 100mm F/6 achomart would have similar color correction to a 150mm F/9.

This does not mean an Achromat is useless, they can be fine instruments, they will lose some detail and resolution on some objects...

Reflectors have no chromatic aberrations so they are also color free, like the APO. THey have issues of their own though.

jon