Polarizer for visual/Quark

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jetstream
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Polarizer for visual/Quark

Post by jetstream » Mon Jun 01, 2015 6:10 am

I have received my Quark back from Daystar and it is working well- no banding, for visual at least. Obviously I've been playing around trying different things and I found that my Baader single polarizer works great for increasing disk contrast-why?!

Also when I rotate the EP/polarizer the view can go from bright to non existent- zero light coming through, why is this?

Thank you
Gerry
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Re: Polarizer for visual/Quark

Post by Valery » Tue Jun 02, 2015 1:29 am

The Quark does polarizing of the entrance light.


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Re: Polarizer for visual/Quark

Post by jetstream » Tue Jun 02, 2015 11:36 pm

Thanks Valery- why would this filter enhance the views? The proms like more light with it and the surface detail less. Does anyone image using such a filter? My views are very good to say the least, I had seeing allowing 200x+ in the SW120ED the other day.

I appreciate the patience :? I hope to understand someday lol! :roll:

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Re: Polarizer for visual/Quark

Post by Montana » Wed Jun 03, 2015 9:14 am

Dear Gerry,
I'm not sure whether this will help answer your question or not, I certainly don't know about the polarizer. Surface contrast is gained when the out of band continuum leakage of light is reduced. Quarks have a very wide base in the transmission curve and this stray light reduces the contrast regardless of the FWHM. You really need to understand this and this might be of help to you
Part2 http://solarnutcase.livejournal.com/9896.html
Part3 http://solarnutcase.livejournal.com/9556.html

I was told by a retailer recently that using a 0.9ND filter cuts out a lot of this stray light making contrast better. This may work in practice but I don't understand how that works in theory. Technically double stacking is the only way to reduce this continuum leakage. I think all this is actually achieving is reducing the brightness of the continuum leakage so it is easier for the eye to see contrast but actually you are not affecting the contrast in the reasons of reducing the bandwidth to see more contrast. I hope this makes sense :)

Maybe others may explain this better.
Alexandra

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Re: Polarizer for visual/Quark

Post by jetstream » Wed Jun 03, 2015 2:32 pm

Thank you Alexandra, the info in your links is fantastic. I briefly read them a while back and am going back for another go at it. The graph of the DS vs the SS shows the difference of the "area under the curves" which makes sense to me.

I never considered that the polariser may reduce out of band leakage- if it does who knows what effect on the curve actually is, rotating the filter will cut off all light in a certain spot. It does increase contrast with my set up's, the ND50% I tried does not curiously. Another interesting thing with the polariser is that near its blackout point the Quark will show banding- or at least appear to. Maybe the light isn't cut off evenly though and appears to band.

Whatever the case may be with regards to the Quark/scopes/filter the views I'm getting approach some of the photos on SC, particularly when seeing allows the use of the 120ED.

Thank you again & it's back to the books ( your articles!) lol!

Best Regards
Gerry
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Re: Polarizer for visual/Quark

Post by marktownley » Wed Jun 03, 2015 7:42 pm

Interesting, something to explore.

Mark Wagner, any further explanation here?
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Re: Polarizer for visual/Quark

Post by mdwmark » Thu Jun 04, 2015 7:57 am

The polariser does nothing with the HW of the filter. The polaroid inside the filter is a circular polaroid. It has two functions.
1) the circular side blocks the internal reflections you will get from the blocker and the etalon mirrors.
2) the linear side blocks the axes that your not using from the mica etalon(mica is birefringent so you have two peaks one for each axes).
If the other axes is not fully blocked(misalign) then the HW will look broader. From the increase of light from that axes.
3) it is probably an optical illusion. Being in Southern California it is not that uncommon to observe the sun through smoke from grass fires. When you do, it looks like your filter has higher contrast. What it is ,is the smoke has cut down the brightness and your brain perceive it as higher contrast.
Case in point: My friends filter needed new blockers, I changed it to use a design that would give him more light. After he checked it out he said the contrast was not as high as before, How could this be, it was the same etalon. So I put back the same designed blockers. He said he preferred it dimmer. The only difference was the brightness.
So using a polaroid to adjust brightness may appear to increase the contrast visibly. But will do nothing for imaging.
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Re: Polarizer for visual/Quark

Post by marktownley » Thu Jun 04, 2015 9:22 am

Thanks Mark :)
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Re: Polarizer for visual/Quark

Post by Montana » Thu Jun 04, 2015 9:47 am

Thanks! that is what I thought :)

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Re: Polarizer for visual/Quark

Post by jetstream » Thu Jun 04, 2015 1:54 pm

Thank you for the explanation Mark!
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Re: Polarizer for visual/Quark

Post by Valery » Thu Jun 04, 2015 6:33 pm

mdwmark wrote: If the other axes is not fully blocked(misalign) then the HW will look broader. From the increase of light from that axes.
Hi Mark,

Can the linear polarizer increase the real contrast in this case of misalign in the filter?

Also, can you express your opinion about possible reason why the Quark has so wide base (skirt) of the transmission curve?
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Re: Polarizer for visual/Quark

Post by swisswalter » Fri Jun 05, 2015 5:52 am

Hi Mark


thank you very much
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Re: Polarizer for visual/Quark

Post by mdwmark » Sun Jun 07, 2015 2:02 am

For Valery's questions,
1) a linear polarizer would clean up a leak from the other axis. You would rotate it till you where lined up with the primary axis your using. I would think this maybe a low level problem.
2) how can a etalon have a longer base then expected. This is a coating problem.
With an solid etalon you need to coat both sides. Let say one side is a little long or short from the center wavelength design or both side miss the correct center wavelength design. Then you may have a peak at the right wavelength but at the bottom of the curve it will be not be as low as it should be. This will make the base look longer. The image will loose contrast at the same HW. This is a classic signal to noise problem.
Mark W.

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Re: Polarizer for visual/Quark

Post by Valery » Mon Jun 08, 2015 3:21 am

Thanks, Mark W. for your perfect clarification.

Valery.
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Re: Polarizer for visual/Quark

Post by marktownley » Fri Jun 12, 2015 8:23 am

I tried the polariser on the ep I was using visually on the quark and the effect is quite positive. I must try it with my imaging rig to see if there is a leak from the other axis, another experiment to try at some point!
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Re: Polarizer for visual/Quark

Post by Valery » Sat Jun 13, 2015 1:54 am

marktownley wrote:I tried the polariser on the ep I was using visually on the quark and the effect is quite positive. I must try it with my imaging rig to see if there is a leak from the other axis, another experiment to try at some point!
Hi Mark,

I need to do the same.
"Solar H alpha activity is the most dynamic and compelling thing you can see in a telescope, so spend accordingly." (c) Bob Yoesle.

Largest full size 185 - 356mm Dielectric Energy Rejection Filters (D-ERF) by ARIES Instruments.

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