Lunt Ca-K 1800 diagonal, ZWO160mm, SW ED100 focus issue

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Jordan Konisky
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Lunt Ca-K 1800 diagonal, ZWO160mm, SW ED100 focus issue

Post by Jordan Konisky »

Hello Everyone,

I've been off SolarChat for a few months recovering from a hip replacement. A few days ago my surgeon cleared me for all activities, so I thought I would try out my new ZWO 1600mm, new Lunt 1800 CaK diagonal in combination with my StarWatcher ED ED100 refractor for my first try at CaK imaging. It turned out to be a frustrating return to solar imaging.

I first tested the camera using a Baader WL filter and found that bringing the camera to focus required cranking the focuser down to within a cm from the forward stop. As expected, same result when I stopped down to a 50mm mask.

I next removed the WL filter and replaced the SW diagonal with the Lunt 1800 diagonal module. I was able to insert only half of the Lunt 1800 nose before it came to a stop up against an internal lip. This arrangement did not come to focus on my SharpCap capture screen. 2X Barlow or TV 2X Powermate had no effect. Suggestions?

Jordan


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Re: Lunt Ca-K 1800 diagonal, ZWO160mm, SW ED100 focus issue

Post by krakatoa1883 »

This is a well known problem of some (not all) SW ED refractors, a step inside the mobile tube that prevents inserting long 2" accessories. There is no solution other than replacing the focuser as I made with my own 100ED. I suggest a Baader Steeltrack focuser, this will solve the problem with the WL filter too.


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Re: Lunt Ca-K 1800 diagonal, ZWO160mm, SW ED100 focus issue

Post by Jordan Konisky »

Yeah, I thought this might be the case. Which model of the Baader Steel Track Focuser would you recommend for my SW ED100 refractor. The nose of my Lunt Ca-K diagonal is 9cm. I very much appreciate your explanation and suggestion.

Jordan


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Re: Lunt Ca-K 1800 diagonal, ZWO160mm, SW ED100 focus issue

Post by krakatoa1883 »

The focuser is this one
steeltrack.jpg
steeltrack.jpg (36.84 KiB) Viewed 368 times
In the USA Baader products are sold by AlpineAstro, so you can order from this page

https://alpineastro.com/collections/foc ... ck-focuser

together with the adapter for SW tubes

https://alpineastro.com/collections/foc ... -celestron

The adapter shall be attached to the tube by using of the same screws of the original focuser, it's a minute-long adaptation, very simple. The Steeltrack saves lot of backfocus compared with the original SW focuser, this will make the scope much more usable, particularly for imaging. No steps inside, the Lunt CaK nose can be fully inserted. The finder base in the image above is not included with the focuser, it shall be purchased separately.

Hope it helps


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Re: Lunt Ca-K 1800 diagonal, ZWO160mm, SW ED100 focus issue

Post by marktownley »

Where abouts is the lip in the focuser tube?


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Re: Lunt Ca-K 1800 diagonal, ZWO160mm, SW ED100 focus issue

Post by Jordan Konisky »

Mark,

The lip is 4.5 cm from from where the diagonal gets inserted. As I recall, a few days ago Alexandra mentioned such a lip in one of her refractors while trying to insert the her Lunt Ca-K diagonal.
Jordan


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Re: Lunt Ca-K 1800 diagonal, ZWO160mm, SW ED100 focus issue

Post by marktownley »

Is it midway along the draw tube or at the end? Can you post a pic?


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Re: Lunt Ca-K 1800 diagonal, ZWO160mm, SW ED100 focus issue

Post by Jordan Konisky »

The lip is, in fact, a slight narrowing of the entire draw tube that begins 3cm from the end where one inserts the diagonal. It, thus, acts as a barrier to full insertion of the Lunt Ca-K 1800 diagonal.


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Daystar Quark H-Alpha Chromosphere
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Lunt White Light Solar Wedge
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Re: Lunt Ca-K 1800 diagonal, ZWO160mm, SW ED100 focus issue

Post by Jordan Konisky »

krakatoa1883

I appreciate your taking the time to provide me with the details for the Baader Diamond Steeltrack Focuser and adapter. Pretty close to pulling the trigger on an order.

Jordan


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Lunt CaK B1800 Filter Module
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Re: Lunt Ca-K 1800 diagonal, ZWO160mm, SW ED100 focus issue

Post by marktownley »

Jordan Konisky wrote: Sat May 15, 2021 3:03 pm The lip is, in fact, a slight narrowing of the entire draw tube that begins 3cm from the end where one inserts the diagonal. It, thus, acts as a barrier to full insertion of the Lunt Ca-K 1800 diagonal.
Ahhh, I understand. If it was right at the very end I was going to suggest cutting the very end of the drawtube off. If it's a taper only 3cm in this approach wouldn't work. I replaced the focuser on my ED80 for the same reason.


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