Quote:
Originally Posted by multiweb
+1 . as other said you'll have no trouble at all for NB or if you collect colors separately. The only time you'll want an apo is when you shoot with an OSC. My QHY8 with the ED80 for example of Pentax lens had always blue channel blurred. No problem otherwise.
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The only reservation I would have is that lenses can vary in their performance on various colour channels. So it may be sharp in green but poor in red. Dr Rohr tests lots of scopes and you can see that in his tests. Often scopes will be good with little aberrations in one colour yet lousy in blue for example.
APOs tend to be good in all channels but even then they are often weak in one.
As I recall my FS152 Tak was quite weak in blue so blue ringed stars often occurred. I can't remember now if I did an image where I focused each channel. I think at one stage I did that and I still got some blue ringed stars.
Why?
Because the blue subexposures had much larger stars as the lens did not perform as well in the blue spectrum.
So that is still likely to occur. But I have been advised for example with the Pentax 67 300mm F4 lens that it would be good for NB but would shot chromatic aberration in colour shots.
So it might be a bit of trial and error to find out. NB though are so narrow that it may work fine. No guarantee though.
Greg.
