2 replies to this topic

[GA-HAMAL]

One day, testing the filter Baader SII 1.25 ", using my amateur spectroscope, got such a picture



But, after using a long shutter speed, I got a photo was


 
thought it might bug, so I connected the camera Atik Titan OSC filter Baader SII and filter IRcut GSO and GSO Green filter for suppression of the spectrum red light, and got the green bushes.

Baader SII and IRcut GSO and Wratten GSO #58


Telescope Newton 76/350, without chromatic aberration.

This is probably obvious why I used the filter IRcut GSO

IR UV

instead of filter IR / UV cut Baader

IR UV
 
You can question my research with the spectroscope, but you can not question the green plants. 
What do you think about this fact?

[noisejammer]

Ok, it's pretty obvious that some green is getting through.

 

TL;DR : The important thing to realise is that the green transmission is FAR fainter than the SII line.

 

When designing an interference filter (I used to do it for microwaves but the idea is the same), you have to accept that a filter will not have complete rejection across its stop band. In practice, the stop band may suppress the leaking signal amplitude by three or four orders of magnitude ... so that the leaked power is suppressed by 6-8 orders of magnitude. This is the same as knocking a first magnitude star down to 16m - 21m ... No, it's not infinite but it's not particularly problematic either.

 

Can I suggest you try to measure the leakage in the green part of the spectrum. Use a green dye filter to obtain a baseline then use the green dye filter + the SII filter. Compare the photon counts on a bright star.

 

Edit - another thought

Since the SII line is at 672.4 nm, it is almost certain that the filter will leak light at 672.4 / 3 or 224.1 nm. This is a fact of life with interference filters. Of course, 224 nm is quite hard UV and is absorbed by the atmosphere so - in practice - there's nothing to see. As an aside, the substrate will also absorb hard UV, but that's somewhat tangential.

[GA-HAMAL]

I know this is obvious, I know, it is much weaker, I wonder, however, why this is not on this chart? In my opinion, it is not so weak as not to appear on the chart. Is it my fault that I'm so inquisitive, at what I do ? Nobody else has not reported similar observations.