Learning to get 'on-band'

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rbenton
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Learning to get 'on-band'

Post by rbenton »

I have added a DSII to my Lunt LS100 and I am quite confused about the tuning. The instructions are not too specific so I feel like I am just blindly twisting the tuners until it looks good. There must be a better method than this. Even so, my best efforts result in a full disc which is not entirely "on-band." I see good detail in part of the disc, but not all. When I increase exposure to see the proms I see a hot spot which seems to be spoiling the image. I will attach a pair of frames that illustrate my issue. Except for moving the disc within the frame all settings are the same. I have also attached a third frame of the proms w/ hotspot. My setup is Lunt LS100, DSII and the camera is a 6mp PGR Grasshopper3. What am I doing wrong?

Thanks,
Randall Benton
offband1.jpg
offband2.jpg
Hotspot.jpg
Hotspot.jpg (173.89 KiB) Viewed 707 times


OTangen
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Re: Learning to get 'on-band'

Post by OTangen »

Hallo Randall!

I have the same Lunt you have and I do the following if I am not sure I am inband: First I remove DS2 and adjust the first filter for maximum contrast and detail, then I add DS2 and tune for maximum brightness while still maintain detail and contrast. Then I tune the first and second filter small amounts, like a quarter of a turn, to try to get an even illumination and keeping the whole field of view inband. To achieve even illumination I sometimes adjust the exposure so that the image on the screen is just washed out. That way it is easier to see if parts of the disk is correctly illuminated. If it is difficult the achieve even illumination I rotate the ERF in the focuser (mine is mounted there, but yours may be mounted in the diagonal) till I get as even illumination as possible. When you have found the right position of the ERF, you can carefully rotate the ERF itself so that the focuser knob is positioned where you want it.

Here you can see my earliest attempts at getting it right:

http://www.knuttangen.no/astro/index.ph ... March-2014

The glare in the left part of the image is something I have too. I got a new filter in front of the DS2 that Lunt sold at NEAF in 2015 and that helped quite a bit, but there is still more light on the left side than on the right side of my full disk images.

Hope this can give you some ideas on how to tune to maximum performance. The Lunt100 DS is a great piece of equipment that I hope will give you many wonderful experiences. Mine has anyway :)

Best regards
Oivind Tangen
60N 10E

See http://www.knuttangen.no/astro/index.ph ... un-in-2016 for my latest solar images.


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Re: Learning to get 'on-band'

Post by marktownley »

Sage advice!


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rbenton
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Re: Learning to get 'on-band'

Post by rbenton »

Thanks for the advise OTangen. I will try this today. Can you describe how to rotate the ERF in the focuser? It sounds like you have the B3400 which is what I have as well. I removed the focuser, but I don't see how to rotate the ERF within it. Anyway thank you very much for the suggestions.

Randall Benton


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Re: Learning to get 'on-band'

Post by OTangen »

Hi Randall!

Yes, I so have the B3400 filter. To rotate the filter, I had to make a tool consisting of two small nails protruding a piece of flat wood. BE EXTREMELY CAREFUL WHEN YOU ROTATE THE FILTER. I measured the distance between the two small holes in the filter with a caliper, drilled the holes in the piece of wood. Then I very entered the nails into the piece of wood. Now comes the part where you have to be very careful: Entering the two nails into the small holes in the filter. I knew how much I had to rotate the filter from trial and error with rotating the whole focuser. I used i tiny drop of Locktite to secure the filter after having checked that field was more evenly exposed. BUT BE CAREFUL so you don'n accidentally scratch the filter with the nails or caliper.
Hope it works well for you, and it is easy to try it out by just rotating the whole focuser. May be you need to rotate it 180 degrees, then you do not need to mess with the filter at all, just turn the tube 180 deg. :)

All the best from
Oivind Tangen
60N 10E


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