How to use the DS ethalon on Lunt50?

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How to use the DS ethalon on Lunt50?

Post by Taipan » Fri May 22, 2020 7:53 am

How do you use the DS filter on Lunt50? When i use the filter the pictute is wery uneven lit. I don't turn the knob on the filter at all. If i do the sun starts to burn out from one side..
Do you rotate the DS-filter on the scope to get it right and let the filter IN the scope do half the sun and the DS tha other?(do you understand?)

Usually i dont use tha knob on the DS, do focus and turn the ethalon in the scope. Then move tha sun around on the sensor to fint a sweatspot where the sun is nicely litt... Play arount a little bit with exposure and ethalon..

Lunt LS50THa/B600PT SS. ZWO ASI 120MM-S. Skywatcher Esprit 80ED with homemade Baader solarfilm filter and solarcontinuum filter.

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Re: How to use the DS ethalon on Lunt50?

Post by Merlin66 » Fri May 22, 2020 8:53 am

Most secondary etalon filters require some “clocking” ie rotating relative to the front of the scope to find the best alignment.

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Re: How to use the DS ethalon on Lunt50?

Post by marktownley » Fri May 22, 2020 10:22 am

Tune the Lunt50, put the DS etalon, tune it so the secondary reflection is just off the disk.

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Re: How to use the DS ethalon on Lunt50?

Post by EGRAY-OBSERVATORY » Fri May 22, 2020 11:23 am

Morning Taipan

Using my Lunt LS60 and its' DS, I normally adjust the LS60 on it's own first for a very-sharp visual-image of the edge of the Solar-disk. That is always important throughout any session with or without the DS attached, by very careful adjustment of the focusing draw-tube of the scope. If possible then to lock that scope's draw-tube, as otherwise when adding the DS, it is likely the focusing will change. That should be achieved by using a zoom-eyepiece (8-24mm) or around a 20-24mm EP for a short-Refractor at least...

Adjust the LS60's Etelon to the desired view as either prominences, or surface detail/S.spots (should they ever appear). Once done, have a good look around the disk and proms and enjoy those views before applying the DS, as often by tuning the Etelon a little either-side you will likely see other facets of the Sun and what is happening at that time.

Adding the DS, should of course increase the contrast of the previous view, but it's own Etelon also needs to be carefully adjusted before any further adjustment to the (first)-LS60's Etelon. Carefully adjusting the DS Etelon, should get you near to the nice contrast "sweet-spot", when also to check the Solar-limb for any focus-correction of the scope's draw-tube, which might need tweaking - a very little.

Any slight-adjustments between the DS and the LS-60 (in my case) requires only quite small adjustments and if one over-does any adjustment of either Etelons, simply go straight-back with that adjustment to it's "sweat-spot" and if needed, by doing the same with the other Etelon.

It can be a little like a "cat and mouse" game chasing between the two Etelons and does require some practice to get the best of proms, surface- detail and spots, but worth the effort. Also if suddenly the image disappears through the EP etc., take a look at the ground and see if any clear shadows are around (caused by the Sun and clouds in the way ???)... Even when I am imaging, that can be quite frustrating - so patience there).

Just to repeat, that at any stage the scopes-focusing needs to be accurate, as the fine detail will be merged and not experienced (or even seen at all).

The "burning out" that you mention is just a part of tuning both Etelons for that "sweat-spot" and is not a sign that anything is necessarily wrong.

You also say "Do you rotate the DS-filter on the scope" - NO, the DS filter (Double-stack unit) must always be tight-enough on the scope throughout.
In fact as the DS itself can be a tad-heavy for its' size, when trying to fit or remove it from the LS50/60 etc., it could even slip from one's hand, with devastating damage, costing around £500 or more to replace. My recommendation would be to get some large-enough rubber-bands and completely surround the outside of the DS, which greatly-assists the safe-handling... (I know from my experience in the past)...

"Usually i don't use the knob on the DS, do focus and turn the ethalon in the scope." you have said, I've never tried that and in any case using the correct eye-piece as previously mentioned and adjusting either Etelons' knobs is the way to go... It should never-ever be necessary to turn the DS's body instead of the Etelon adjusting knobs and I would never advise anyone to do that for my previous advice above... (a few too-many turns - could prove disastrous)... Tune the two Etelons as suggested previously here...

You do also add "Play around a little bit with exposure and ethalon.."
For imaging with either a digital (or film-camera) and especially for using dedicated astro-CCD type cameras, adjustment will always be needed to be correct by trial and error as either too dark/light or even out of focus - will occur.
Of course with any digital-cameras, just keep shooting until one gets the correct results... That costs nothing except time and error...

I trust that helps a little with your question and ideas Taipan.

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