Lunt 80DSII vs 100DSII

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pbsastro
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Lunt 80DSII vs 100DSII

Post by pbsastro » Sat Jan 10, 2015 2:51 am

Hi all,
I am mainly a visual guy, I like to look through the eyepiece and discuss equipment, not so much photos. That is why double stack is more important to me.
It is well known that double stack with two internal etalons works not as perfect as a internal etalon with an external etalon. However at 80 and 100 aperture cost is lower with full internal etalons. It is a compromised solution and it seems to me Lunt chose different compromise on the 80DSII vs the 100DSII. I would like your opinion on this.
From what I see the 80DSII and 100DSII are a bit different, and people reports about them also differs.
It seems to me people report the sweetspot is better on the 80DSII, but the 100DSII has less halo (ghost reflection). I think this matches the differences I find in the etalons positions, from photos:

http://www.lunt-solarsystems.eu/index.p ... mmerce_pi1[showUid]=691&tx_commerce_pi1[catUid]=9&cHash=fccbcd862e83e0a75ef9580211e4a186

http://www.lunt-solarsystems.eu/index.p ... mmerce_pi1[showUid]=835&tx_commerce_pi1[catUid]=10&cHash=77e187e04a18641389973730176516d8

With 80DSII the etalons are placed very close, with the tuning knobs almost touching, while with 100DSII, the etalons are placed very far apart. The 100DSII is very long getting near to the main etalon, but I think that the etalons are aligned with the tuning knobs, and the black extension tube on the 100DSII is just an anti-reflection filter between the etalons.

Now, the sweetspot is defined by distance from etalon to focus point. The farther from focus the better the sweetspot.
The ghost reflections are defined by the distance between etalons, The farther apart the less halo.
So, the second etalon in the 100DSII is farther from the first etalon, but closer to focus. Following the reasoning above that explains the differences I think I detect on people reports.

Can anyone please measure the distance from focus to tuning knob center of the second etalon. And the distance from focus to tuning knob center of first etalon when in single stack mode. That would help me confirm my reasoning, and better understand 80DSII and 100DSII differences.

Thank you for any comment.
Pedro

SMS
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Re: Lunt 80DSII vs 100DSII

Post by SMS » Mon Feb 09, 2015 3:08 pm

Hi Pedro,

I'm a visual observer too, I leave the photography to the awesomely talented people on this forum but I thought I would mention a memorable viewing experience. I recently purchased a Quark and when double stacked in my Coronado SM60 it produces a full disk view in binoviewers that rivals some of the best photographs. You just need to use a standard mirror diagonal instead of the BF diagonal. There was no sweet spot or banding and the contrast was fantastic.

Clear Skies,

Steve

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Valery
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Re: Lunt 80DSII vs 100DSII

Post by Valery » Wed Feb 11, 2015 2:49 am

SMS wrote:Hi Pedro,

I'm a visual observer too, I leave the photography to the awesomely talented people on this forum but I thought I would mention a memorable viewing experience. I recently purchased a Quark and when double stacked in my Coronado SM60 it produces a full disk view in binoviewers that rivals some of the best photographs. You just need to use a standard mirror diagonal instead of the BF diagonal. There was no sweet spot or banding and the contrast was fantastic.

Clear Skies,

Steve
Hi Steve,

I politely, but completely disagree. I have used a very narrow (0.38A) Quark double stacked with Lunt LS50F Ha internally installed in a 150mm F/5 telescope.
The view is contrasty, of course, but is not even close to what can be achieved with CCD camera at high resolution.

Valery.
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Re: Lunt 80DSII vs 100DSII

Post by Gert » Tue Mar 17, 2015 7:22 am

Hi,

I have tested the LS100 with the internal DS unit. The DS vs the SS has quite strong ghosting. Here is a combinations of photos showing the reflections.

http://drgert.dyndns.ws:8000/download/LS100DS_Halo.jpg
You can see in the photosequence how I rotated the DS unit (keeping the BF and camera combo at same angle). It shows the ghosting at the same location. I also did another experiment rotating the BF/camera unit keeping the DS unit fixed. (Just haven't uploaded the photos yet) Surprisingly there, too the ghost was stationary in the same angle. Maybe the optics experts here can use that evidence and point out which lens is at fault. i would like to provide feedback to Lunt and ask if there is a remedy to the situation.

Clear Skies,
Gert
Gert Gottschalk, Ph.D.

Tri-Valley Stargazers, Eastbay Astronomical Society, WFS Berlin

Derek Klepp
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Re: Lunt 80DSII vs 100DSII

Post by Derek Klepp » Tue Mar 17, 2015 10:09 am

Thanks Gert

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Re: Lunt 80DSII vs 100DSII

Post by swisswalter » Wed Mar 18, 2015 5:14 am

Hi Gert

that is really severe ghosting. Hope you can fix that
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Re: Lunt 80DSII vs 100DSII

Post by marktownley » Wed Mar 18, 2015 6:56 am

Very bad ghosting! Contact Lunt, definitely.
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