Poor single stack but nice double stack

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Marcus444
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Poor single stack but nice double stack

Post by Marcus444 » Mon Oct 02, 2017 5:26 pm

A few weeks ago I bought a Lunt LS60 PT with 60mm double stack unit. The LS60's pressure tuner requires almost every last mm of travel to produce surface detail - which in single stack is barely apparent. Only the slightest mottling on the surface and limited prom definition. Yet I'm reasonably happy with the double stack views (apart from wishing that the PT didn't have to be screwed in so tightly). So here is my question:
If an HA scope shows very little detail in single stack, does that inevitably diminish the double stack view? I.e. Even though I'm getting good results, could they be better?
Or Is it perfectly possible to have poor SS views - yet great DS views - so the internal etalon's performance can be transformed by a well matched external etalon?
I previously had a LS50 which was double stacked - so I'm very familiar with the way these scopes work and the benefits of DS. Obviously my next step is to replace the o-rings and re-grease, but beforehand I wanted to gauge the opinions of this excellent forum.
Thanks
Lunt LS60THa + 60FHa
Takahashi FC-100DC + Lacerta Herschel Prism
Leica ASPH and Pentax XF zooms
TV plossls and Fujiyama orthos

Marcus444
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Re: Poor single stack but nice double stack

Post by Marcus444 » Mon Oct 02, 2017 5:53 pm

PS: haven't posted much on solarchat before so wasn't sure if the above should be on the main forum thread???
Lunt LS60THa + 60FHa
Takahashi FC-100DC + Lacerta Herschel Prism
Leica ASPH and Pentax XF zooms
TV plossls and Fujiyama orthos

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robert
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Re: Poor single stack but nice double stack

Post by robert » Mon Oct 02, 2017 6:07 pm

PS if you cannot get a maximum contrasty ss image you will be losing out on the ds quality in my opinion.
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Re: Poor single stack but nice double stack

Post by robert » Mon Oct 02, 2017 6:09 pm

I have a similar setup. I am able to screw the tuner in to best contrast and then beyond that to poor contrast again in single stack. The pressure in the etalon sometimes has to be equalised with ambient pressure by unscrewing until the o ring is released. It hisses slightly.
Do you occasionally equalise like this. If you have and still cannot pass the optimum tuned point there is something wrong and it could be a leak as you suggest. O ring grease etc...

Good luck
Robert
images and animations http://tinyurl.com/h5bgoso
2018 images https://www.flickr.com/photos/69734017@ ... 1234171714
2017 images http://tinyurl.com/gvk9k3k
ED80. SW200. ES127. Celestron-150mm-PST mod
LS60PT-LS60F-B1200. B600-Cak. PGR-Ch3-IMX265

Marcus444
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Re: Poor single stack but nice double stack

Post by Marcus444 » Mon Oct 02, 2017 8:58 pm

Thanks Robert. I've unscrewed the tuner many times (on both my Lunt scopes) and never heard the slightest hiss, woosh or pop. So new o-rings is obviously the way to go. I have lots more experimenting to do before I can post a full review of this scope - but I was surprised at how good the double stack views were considering the disappointing SS views.
Lunt LS60THa + 60FHa
Takahashi FC-100DC + Lacerta Herschel Prism
Leica ASPH and Pentax XF zooms
TV plossls and Fujiyama orthos

Live_Steam_Mad
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Re: Poor single stack but nice double stack

Post by Live_Steam_Mad » Thu Jan 18, 2018 4:20 pm

Interesting, I have LS50 and I also never heard anything when equalising my pressure tuner (which I have done many, many times). My single stack views already have quite a bit of surface detail and good contrast also on the surface (proms are also bright and detailed) so I can't wait to try the double stack. I'll have to buy the DS second hand I think as it's very expensive.
How did you find your LS50 in single stack? It sounds like your particular LS60 doesn't show much better performance on the surface than your LS50 did?
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Bob Yoesle
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Re: Poor single stack but nice double stack

Post by Bob Yoesle » Sat Jan 20, 2018 2:58 am

As opposed to tilt-tuned etalons, air-pressure tuned etalons are made with a CWL to the blue side of the H alpha line. As noted previously, you should be able to increase the pressure to come on-band, and then with more pressure pass into the red wing with diminishing chromosphere detail. It sounds like you might have an etalon issue - the etalon may have a low a CWL, and it would need more pressure to come on band. This issue will be exacerbated if you live at a higher altitude. It may work just fine in Death Valley... Should still be under warranty, so I would discuss with Lunt directly, as they have very well regarded customer service.
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