Measurements of a Coronado SM-40 Ha filter and BF5 - Ha lamp

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christian viladrich
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Measurements of a Coronado SM-40 Ha filter and BF5 - Ha lamp

Post by christian viladrich »

Hi,

"Thanks" to the current bad weather, I spent some time testing another Coronado SM-40 with the Ha lamp

This is the second one I tested. The first one was 0.74 FWHM, but this second one is 0.95 A FWHM. It 0.9 A away from the center of Ha at normal incidence.

If I am not mistaken, the SM-40 was supposed to have a FWHM < 0.7 A ?

When the Sun is back (if ever ...) I try and test the BF 5 with the spectro.

More results here :
http://astrosurf.com/viladrich/astro/in ... -40_2.html

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Re: Measurements of a Coronado SM-40 Ha filter - Ha lamp

Post by marktownley »

Thanks for the info Christian. This second etalon is not the best :(


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Re: Measurements of a Coronado SM-40 Ha filter - Ha lamp

Post by christian viladrich »

Hello,

I now have tested the BF5 (more precisally the whole BF5 diagonal).

The FWHM is 6.9 A. The offset from Ha is +1.5 A, which is not a big deal. This is a 2-cavity filter.

http://astrosurf.com/viladrich/astro/in ... an2022.jpg


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Re: Measurements of a Coronado SM-40 Ha filter - Ha lamp

Post by marktownley »

Thanks Christian, all good information!


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Re: Measurements of a Coronado SM-40 Ha filter and BF5 - Ha lamp

Post by christian viladrich »

Hi,
Just to say I put some more results in the following webpage:
http://astrosurf.com/viladrich/astro/in ... -40_2.html

I am afraid it's quite technical. The new stuff (test in collimated light) is about the mapping of the CWL drift over the aperture of the etalon. In other words, it is about assessing the uniformity (or not) of etalons.

Given the low altitude of the Sun in winter, I have two more months to work on these. Then, I go back to imaging ;-)


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Re: Measurements of a Coronado SM-40 Ha filter and BF5 - Ha lamp

Post by marktownley »

Very interesting thanks Christian, I will flag this for my weekend read :)


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Re: Measurements of a Coronado SM-40 Ha filter and BF5 - Ha lamp

Post by Bob Yoesle »

Just want to add to Christian's work that etalon tuning and uniformity using a collimator can also be observed visually by having the etalon/telescope system aimed at the Sun and removing the eyepiece (keeping the BF in place) and viewing the etalon "surface" directly. This also represents illuminating the etalon with collimated light (~ f109). Once the etalon is on-band it will have the most uniform and brightest appearance obtainable (as in the middle figure shown by Christian for the SM40). Any variation in brightness represents a variation in the CWL of that area of the etalon - variation in etalon gap spacing.

Here's a simulation of what tuning an etalon to be on-band generally looks like going from left to right. I have successfully used this method to perfect the tuning of both single a double stacked front and front/internal etalon systems.

Etalon uniformity.jpg
Etalon uniformity.jpg (101.45 KiB) Viewed 955 times

More on this topic can be found here.


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