The cheaper ones are just basically a light yellow filter , the more expensive ones eg. Baader ' Semi APO ' do quite a good job , I used one for years on my Saxon 150mm f8 Achro ( yard cannon ) and enjoyed the results before getting a Chromocor made by Aries in Russia , these really work but very expensive .
This set up with the Chromocor compared well to a friends 152mm Astro Physic's f8 Starfire APO ( $7000 ) on all objects up until about 350x then the APO took the lead as it stayed sharper than my $1200 Achromat at those high powers .
I did find that the ' Semi APO ' style filters worked well in the 6 inch refractor but dimmed the image quite a bit in the 3 and 4 inch achromat's I had at the time .
Brian.
Quote:
Originally Posted by Ukastronomer
Even more confusing is, is a Semi Apo Filter what it says, or just a fringe killer ???
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