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How to differentiate filters among each other

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3 replies to this topic

#1 Saturn668

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Posted 17 August 2019 - 10:05 AM

So we were setting up the ZWO Electronic Filter Wheel and placing ZWO LRGB and Narrowband filters in them. However, we forgot to screw them in and they all fell. While they weren’t damaged, we now aren’t really sure which filter is which. We are pretty sure about the LRGB ones, but we’re especially unsure about the narrowband ones. We currently concluded that the one with the very slight red-ish tint is the Hydrogen Alpha (other than that it’s just like a boring mirror), the OIII filter seems to have a bit of chromatic abberation-esque effect and finally the yellow tinted one is SII. Are these correct? Once I start imaging, is there a way for me to confirm these placements?



#2 pfile

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Posted 17 August 2019 - 10:17 AM

which filter is Ha should be pretty obvious on any nebula - the baryonic universe is like 99% hydrogen so that's the strongest signal out of the 3 narrowband filters, by far.

 

as for the others, well, both OIII and SII are pretty weak signals, so it's a little bit harder to tell by eye. probably any planetary nebula that's mostly blue is going to show up in the OIII filter but not show up at all on the SII filter.

 

to be honest there's a way to tell from the color of the filter, but offhand i don't know it. hopefully someone can chime in.

 

rob



#3 bobzeq25

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Posted 17 August 2019 - 10:18 AM

Ignore the surface appearance.  Look at a bright light _through_ the filters.  Ha and S(III) will pass through red light.  O(II) will be blue green, you'll now know which one that is.

 

Take two subexposures of an emission nebula with the same gain and exposure through the other two.  The Ha will be the one that shows you something.  <smile>


Edited by bobzeq25, 17 August 2019 - 10:21 AM.

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#4 pfile

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Posted 17 August 2019 - 10:19 AM

ah right, thanks. the reflected light color is obviously the complement of what passes thru, but if you can get photons thru the filter you'll see the true color.

 

rob




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