LS100 DSll Circular polarizer adapter.

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GUS
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LS100 DSll Circular polarizer adapter.

Post by GUS » Sun Sep 18, 2016 5:06 am

I thought I'd put this here in case someone might find it useful. A while back, Gert Gottschalk posted a thread about the ghosting issue with the LS100 DSII unit and his follow up threads regarding the use of a circular polarizer as suggested by Carbon 60 as a fix for the ghosting. As I was having similar issues, I was also interested in trying the polarizer more for visual use than imaging. I purchased a filter adapter plate similar to the one Gert used and was going to install it on the anti glare filter housing by drilling and bolting to the housing. Before I attempted this, I tried the CP on the DS unit minus the anti glare housing and the image was noticeably brighter without the glare filter. The only issue was how to attach it to the DS unit, initially I taped it on with electrical tape and that was fine, but occasionally I want to remove the filter and use the scope with binoviewers, as the view through the CP was a lot darker especially through one side of the BV. So I purchased a camera lens hood, which has a 49mm filter thread and bought a couple of adapters to fit my CP(40mm diameter). The hood fits snuggly around the threads for the filter housing, but the rubber material was a few mm thicker than the opening of the LS100 tube adapter, so I used a bench grinder with a wire brush, and shaved of enough rubber so that the whole assembly could fit without catching on the adapter. Now I can interchange between the CP and the anti glare filter without any hassle. The view through the CP is great, there is no sign of the ghost image and the suns disk is surrounded by an ink black sky. I went through a couple of filters before finding one that I liked. I've used it up to 200x in great seeing conditions and the detail was the same with and without the CP, but with no ghost image showing at all. The view of a full disk sun is now a pleasure to view without the annoyance of a supperimposed ghost image, and is similar to the quality of my LS60/60 DS scopes view, but with better resolution.

Thanks

Ivan.
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Re: LS100 DSll Circular polarizer adapter.

Post by rxdeath » Wed Sep 21, 2016 4:56 am

nice i want to try this the glare is incredibly annoying can you post part numbers and manufacturers or links to what you bought? you took off the red glass at the bottom and do this instead?

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GUS
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Re: LS100 DSll Circular polarizer adapter.

Post by GUS » Wed Sep 21, 2016 10:55 am

Yes, I took off the red anti reflection filter. The circular polarizer and camera lens hood fit over the threads on the DSII unit. The rubber lens hood is a standard camera accessory, which I purchased at a local camera store, and I also purchased the circular polarizer from the same store. I tried a few different polarizers and picked a 40.5mm (made in Japan) Marumi branded one and bought a few adapters to step down from the 49mm thread on the lens hood. The hood itself when unfurled has a diameter of 69-70mm, which fits over the threads on the DSII unit reasonably tight. I did try another brand of lens hood but it was slightly larger than 70mm and was a loose fit.On another thread, Bob Yoesle mentioned that the B &W Kaesmann circular polarizers are the best optically of the photo CP's.
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Re: LS100 DSll Circular polarizer adapter.

Post by GUS » Thu Sep 22, 2016 2:03 pm

Hi rxdeath, I've sent you an email.

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Re: LS100 DSll Circular polarizer adapter.

Post by rxdeath » Fri Sep 23, 2016 3:39 pm

the good news is i ordreed this and it fit so well that i didn't have to shave anything to fit it in the tube.
https://www.amazon.com/gp/product/B007R ... UTF8&psc=1

however the polaroid circular polarizer i had laying around from my camera kit doesn't allow me to reach focus, i can see the spot of 'most focus', but it is kind of blurry. is this likely from a low quality polarizer?

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Re: LS100 DSll Circular polarizer adapter.

Post by GUS » Sat Sep 24, 2016 4:01 am

Installing the polirizer should have no affect on focusing. Even if it is of poor quality, it still should focus. Did you check to see if the polarizer hasn't come off inside the scope. Can you post a picture of your set up, it might help to see what the problem could be.

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Re: LS100 DSll Circular polarizer adapter.

Post by rxdeath » Sun Sep 25, 2016 4:24 pm

also, i was thinking, their rg is really just what we are trying to do with a different filter...if you wanted couldn't you just pick out the thread locker, undo the retaining ring on the black tube's filter and replace it with an appropriately sized cp?

it says circular PL on the side, and its a polaroid filter
IMG_20160925_091301605.jpg
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IMG_20160925_091315847.jpg (373.92 KiB) Viewed 2016 times
IMG_20160925_091321249.jpg
IMG_20160925_091321249.jpg (281.02 KiB) Viewed 2016 times

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Re: LS100 DSll Circular polarizer adapter.

Post by GUS » Wed Sep 28, 2016 9:26 am

It looks okay, the only thing I noticed is that your lens hood seems longer than mine. My one when installed on the main body of the DSII unit is the same length as when the red glass unit is installed. Maybe check to see if it might be touching the main etalon. You could install the CPL in the red glass holder, but I decided not to, as I prefer to use the red glass when binoviewing as the CPL affects one side of the binoviewer( which is already polarized) and makes the view way too dark. I've got 5 different circular polarizers from different manufacturers and all produce good, in focus images, maybe try another CPL and see how that goes.

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Re: LS100 DSll Circular polarizer adapter.

Post by rxdeath » Sun Oct 02, 2016 6:16 am

ok so i took your advice and fortunately the hood was collapsible and i was able to put it down as shown below:
IMG_20161001_225950.jpg
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unfortunately, the focus problem persisted. so i bought a different cp, and that did the trick. i guess the polaroid one was somehow crappy (visually they look exactly the same), but the polaroid won't go in focus and the tiffen will. i took probably the best mosaic and some of the better full disc pictures i've ever taken, i posted them in my other thread, but here's one, and its not photoshopped to even out the disc, its 100 like that and its probably a 10 pane mosaic, so i'm pretty impressed.

Image

i talk to the lunt people a lot i'll report these findings and hopefully get them to do something about it, or at least advise people about it.

my findings agree with yours, the background is nearly perfect uniform black, and i felt focus was much sharper than i've ever seen it. the annoying glare made life miserable, and i ended up having to rotate the whole scope and take 2 sets so i can get different parts in/out of the glare. thanks for making this madness stop. i'm surprised this isn't 'standard issue' it would be easy to make a swap out for the hrg and size it to fit in there...i bet there will be one soon :) .

for others looking for quick fix these 2 links/product numbers are what worked out of the box for the 100ds unit
lenshood:
https://smile.amazon.com/gp/product/B007RN5WDS
ALTURA FK0138
polarizer:
https://smile.amazon.com/gp/product/B00004ZCAU
TIFFEN 52CP

major props gus

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Re: LS100 DSll Circular polarizer adapter.

Post by george9 » Wed Oct 12, 2016 2:41 am

Just to point out that circular polarizers are directional. There is a linear polarizer and then a quarter wave plate. If you put it in the direction that you would use it in a camera, then the output is circularly polarized and binoviewers will look fine. If you flip it (which could happen if you face the lens hood toward the DSII unit and screw the filter into that), then the output is linearly polarized and binoviewers will show a brighter image on one side. There may be a slight difference in glow reduction. I found it a little better backwards, but both ways are great. Now I just need to check that you don't lose resolution.

George

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Re: LS100 DSll Circular polarizer adapter.

Post by marktownley » Wed Oct 12, 2016 8:45 am

george9 wrote:Just to point out that circular polarizers are directional. There is a linear polarizer and then a quarter wave plate. If you put it in the direction that you would use it in a camera, then the output is circularly polarized and binoviewers will look fine. If you flip it (which could happen if you face the lens hood toward the DSII unit and screw the filter into that), then the output is linearly polarized and binoviewers will show a brighter image on one side. There may be a slight difference in glow reduction. I found it a little better backwards, but both ways are great. Now I just need to check that you don't lose resolution.

George
Very useful to know thanks George!

Interesting thread as well chaps!
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Re: LS100 DSll Circular polarizer adapter.

Post by george9 » Wed Oct 12, 2016 12:27 pm

Just in case Gus doesn't see my post, let me warn readers that you can get different effects. My Denk II binoviewers and Kaesemann circular polarizer work fine when the filter is forward and have unbalanced illumination between the two eyepieces when it is backward. Others may see banding that is not improved by reversing it.

George

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Re: LS100 DSll Circular polarizer adapter.

Post by Gert » Fri Oct 14, 2016 4:15 am

Hello All,

Just a big Hello to Gus to pick up on my tests for the polarizer on the LS100 DS module. I'm happy someone picked up on my work. I recently upgraded to an ASI174 camera and was very pleased to see the added sensitivity of that camera over my older DMK41. With the DMK I had some concerns about the 'mod' as my polarizer had darkened the image and I ended up with exposure times around 20ms (when working with a barlow). With the much more sensitive ASI I can expose at 10ms, which allows me then to go to 100fps AVI frame rate. (I still need a laptop/SSD combo to digest that when recording full frame, though) On top of that the ASI174 captures a full disk image of the LS100 in one shot (no more mosaic'ing). Overall the combo of the polarizer 'mod' with the ASI174 is a truly a winner for me.

You can see recent images with that combination on my 2016 solar observing blog:
http://drgert.dyndns.ws:8000/sun_2016/s ... _2016.html

Clear Skies,
Gert
Gert Gottschalk, Ph.D.

Tri-Valley Stargazers, Eastbay Astronomical Society, WFS Berlin

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