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Filter Stack Freakiness

Discussion in 'Eyepieces, Barlows, and Filters' started by Mak the Night, May 15, 2018.

Filter Stack Freakiness

Started by Mak the Night on May 15, 2018 at 9:28 AM

5 Replies 139 Views 0 Likes

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  1. Mak the Night

    Mak the Night Well-Known Member

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    On my short tube achromats I usually employ a Baader Fringe Killer/Neodymium stack for occasional planetary observing. However, there are times of dodgy transparency when I can use the Fringe Killer stacked with a more conventional contrast filter. If I want even more contrast I sometimes use a Wratten #8 Light Yellow or even occasionally a Wratten #11 Yellow-Green filter. These are traditional minus cyan choices for achromats apparently. I tend to stack the yellow filter in the diagonal nosepiece with the contrast filter behind it in the light train. This is either as a directly connected stack in the nosepiece, or just the contrast filter is threaded into the eyepiece, leaving the yellow filter in the diagonal.

    oddstax (1).jpg

    After a few nights of observing Jupiter near transit with my ST80 during predominantly deep sky sessions, I noticed that the Baader FK/Neodymium stack didn’t always give me the contrast I wanted. This May has had some nice days but there seems to be a dampness in the night air which isn’t helping the transparency (or my recently developed cough). I normally use a Wratten #8 stacked with the Baader Neodymium, or if I want even more contrast, the #8 can be stacked with a TS Optics UCF1 contrast filter. I believed that as the UCF1 could be a little too aggressive for Jupiter’s nuances in this weather a happy medium between the Baader Neodymium and the UCF1 could be found.

    oddstax (2).jpg

    As far as I can determine 'Solomark' is a trademark of Yuyao Qihang Optical Instrument Co., Ltd. Yuyao City, Zhejiang Province, China. The Solomark Crystalview Moon Filter and Solomark Light Pollution Filters are roughly a third more expensive than the Solomark Moon & Skyglow filter. The latter was about £10 (Sterling) which itself is a fifth the retail price of a Baader Neodymium. I believe these filters are also marketed as Gosky. Naturally I tried all of these both in daytime tests and nocturnally. I then discovered something a bit odd. In extremely sophisticated and scientific daylight trials (entailing holding the stacked filters up to a partially closed Venetian blind in bright daylight lol) the stacked #8 and Solomark Crystalview Moon and Solomark Light Pollution Filters produced definite reflective double images. These images were virtually ghosts of the observed light source, almost as if they were reflected from one of the glass filter surfaces. The Baader FK and Neodymium didn’t produce these reflections. The TSUCF1 contrast filter didn’t produce these reflections either (in any combination). Neither did the cheapest of the filters; the Solomark Moon & Skyglow filter! I have no explanation for this. I can only assume the Solomark Crystalview Moon Filter and Solomark Light Pollution Filters don’t have effective anti-reflection coatings, if any. I’ve ordered an OVL Light Pollution filter to compare it with the Solomark. I’m curious as to how it will fare in the ‘Venetian blind’ test. Watch this space.
     
  2. Mak the Night

    Mak the Night Well-Known Member

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    The OVL Light Pollution Filter has arrived, I’d only ordered it yesterday, so I’m guessing it came by bullet train lol. It was £18 (Sterling) and came in the same generic box that most of these filters do now. One interesting difference is that it came with a transmission chart. I’m pretty sure these are the same as the ‘Sky-Watcher’ LP filters. The threads on the OVL seemed to fit everything I tried them with.

    3.jpg

    On closer inspection its housing is subtly different from the Solomark Light Pollution Filter. The actual writing on the housing surface and the circle near the crown are silver coloured on the OVL but white on the Solomark. The OVL housing itself is also slightly taller. Although I can’t see much difference between them by cursory glancing through each one in daylight. Importantly, the OVL passed the ‘Venetian blind’ test, and displayed no ghosting type reflections as far as I could see.

    2.jpg

    In daylight telescope testing stacked with a Wratten #8 the OVL was more like the Solomark Moon & Skyglow filter than the TSUCF1. The transmission seemed about the same as the Solomark. It also had that hint of blue or lavender colour that is quite common with ‘Moon & Skyglow’ filters. This is largely muted on the TSUCF1, but the Solomark Crystalview appears to have an excess of it. When the #8 is at the head of the light train I find this 'lavender effect’ seems to give the yellow filter a more natural feel when viewed through as a stack. I’m guessing it compensates for the cyan wavelength removal by adding back a slight lavender tinge. It will be interesting to try the stack on Jupiter.

    1.jpg
     
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  3. Dave In Vermont

    Dave In Vermont Well-Known Member

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    Does anyone have any idea where a transmission-chart for a Solomark CLS Filter might be obtained? Or have any experience with these?

    Stories short & long most welcome!

    Thanks!

    evaD
     
  4. Mak the Night

    Mak the Night Well-Known Member

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    You could try Yuyao Qihang Optical Instrument Co, as I'm pretty sure they are the 'Solomark' and 'Gosky' OEM.
     
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  5. Mak the Night

    Mak the Night Well-Known Member

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    I just tried the stack on Jupiter. It works well. :):cool:
     
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  6. Mak the Night

    Mak the Night Well-Known Member

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    I managed a grab’n’go ST80 session last night, mainly deep sky, but I observed Jupiter up to transit. The transparency wasn’t very good and was rapidly getting worse. Ideal to test the #8/OVL stack.

    ovl8stack1.jpg

    The sharpest I could get was 125x with a 6.4mm Meade Plossl in combination with a Meade 2x Barlow. The OVL filter did provide a good contrast and combined with the #8 allowed me to see some surface detail. The Equatorial Zone and North and South Equatorial Belts were easily apparent and quite well defined. The Galilean moons were also easily seen and were well contrasted against the filtered background. I didn't wait for the GRS though as the damp was getting to me and the transparency was getting more pants by the minute.



    So I went in and watched an old episode of Juliet Bravo. What ever happened to her? lol

    EDIT: I was convinced I could just see the GRS early on in the session but didn't think it was visible until later. I just checked Sky-Safari, it was the GRS!

    Screenshot 2018-05-17 at 13.23.16.png
     
    Last edited: May 17, 2018

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