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Are the Baader 7nm Ha, 8.5nm Oiii and 8nm Sii parfocal

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I find them pretty close.  some nights there seems to be nothing between them, but other nights there seems to be a difference which I could not fathom out, but I have now come to the conclusion that temperature might make them vary on some nights but not others.  This is testing them all out at the start of imaging.



Edited by carastro
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  • 2 weeks later...
On 28/10/2019 at 00:15, DaveS said:

Physically, yes they are. However, your 'scope might not be parfocal between sulphur and oxygen.

Agreed. With decent filters the non-parfocality comes from the optics.


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I must admit I tend to refocus between filter swaps anyway.  The optics on my Esprit 100 seem to be spot-on though and I don't see much of a difference between narrowband OIII and Ha to date.  Would the same apply to RGB, do folks think?  As the OP says, it would save a lot of time.  I've not tried out pure LRGB unbinned with the new scope yet - and given the UK south-east autumn weather, it may be a while.... 

Edited by Hallingskies
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On 27/10/2019 at 21:58, Bepis said:

As title stated, are they parfocal? Really don't want to refocus everything I switch filters...

As above, they might be but its unlikely your scope is so I would not worry too much about it. 

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