Hi Ray,
I should have been more clear that I was after 2" filters so that they may fit in my filter slider (not using a wheel).
Thanks for the informative response. It looks like it isn't worth spending the money on the cheap filters and one is better off saving for the Astronomik/Astrodon/Baadar filters instead? The Orion LRGB set was looking tempting but i'm not so sure now
Thanks again.
Quote:
Originally Posted by Shiraz
Sorry Mohammed, I didn't notice the filter size - assumed you would be looking at 1.25 for planetary. Your choice, but you really don't need 2inch filters for planetary imaging (where you will be using a tiny chip at f25).
From my limited experience, things that I would watch out for with any filters you buy are:
1. AR coating on the non-filter side to maximise transmission and remove any possibility of image-destroying reflections - the sharpening process can enhance even slight step anomalies in planetary images - big problem,
2. hardness of the coatings (you will need to be able to clean them when imaging at f25)
3. supression of IR leakage, which can muck up colour rendition. If you need to put in a separate UV/IR blocking filter, you will lose sensitivity and increase cost.
4. quality of the substrate - it is nice to have truly parfocal filters so that you do not need to refocus between colour runs - you will only get that if the maker has paid close attention to the substrate optical quality.
The relatively low in-band transmission of the Omega filters suggests that they possibly do not have AR coating on the back side. they also do not show transmission curves out to 1 micron, so there is incomplete data on IR blocking. If you do decide to buy them, would be worth checking with the makers to determine if they are AR and have full IR blocking.
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