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Old 23-03-2017, 07:39 PM
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Prickly is offline
Join Date: May 2007
Location: Canberra
Posts: 340
I think the light yellow is similar to the semi apo but the semi apo has no noticeable colour hue. Yes the semi apo filter cuts out light but mostly where you want it removed. There is good transmission (90% approx) for Ha, Hb and O3. But you will lose light in the yellow (light pollution region) and the blue (which causes the blue fringing). It doesn't cut out quite enough of the blue though. The contrast booster cuts in around 470 nm but the semi apo more at around 450. Looking through the semi apo I think it gives good light transmission in that it is not like looking through a nebular filter but you do get a bit more contrast. I'll have to see if I can track down a 495 filter at SPSP.

Note my comments are mainly based on suburban use with a 140mm refractor (pretty close to 6 inches)

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