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Questions about our new Quark setup, diagonals and suggestions.

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Questions about our new Quark setup, diagonals and suggestions.

Hi All,

I've not been on here for a while and have hardly had a chance to the see the light of night this year.

Quick history. My wife, Averil(Yarn) decided she wanted to buy a solar scope set up. It had to be simple(ish) to use and without polar alignment hasels. We weighed up Lunt and Quark etc. and with a modest budget, finaly settled on and bought the following:

Quark Chromosphere.

SW Discovery Alt/AZ mount.

A handfull of SW plossls.

A few other bits to glue it all together.

The plan was to use my old ST80 (ex guide scope) So we got a TS Crayford focuser as well.


Now then, same old story, lack of back focus with the planned setup (or some would say front focus, depending in the minus sign).

Some measurements at infinity focus:

All with SW ST 80 + TS focuser + low profile (zero length) 2 inch to 1.25 inch adaptor

10mm Plossl + ST80 + SW cheap 45deg 1.25 prism = 41mm Draw tube

10mm Plossl + ST80 + WO 45deg 1.25 prism = 33mm Draw tube

10mm Plossl not possible with draw tube.

10mm Plossl +61mm extender (improvised) 73mm Draw tube = 134mm

Quark + 25mm Plossl = 69mm Draw Tube

Quark + 10mm Plossl = 72.5mm Draw Tube


Some Calculations:

SW cheap 45deg 1.25 prism = 134-41mm = 93mm optical length

WO 45deg 1.25 prism = 134-33mm = 101mm optical length

Quark = 134-72.5mm = 61.5mm optical length



Quark + Diagonal < 134mm

Required Diagonal < 134 - 61.5 = 72.5


Finally my questions:

Do my calulations make sense?

Does any one know of a 1.25inch (or even a 2inch) 90deg diagonal with a total optical length of <70mm?

Any suggestions to convert this into a decent solar setup without breaking the bank?


Thanks in advance.

John (and Averil)


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well i can't add technical feedback but i can say congratulations on your wife wanting a solar setup, where do you find wives like that? lol mine just complains and nags whenever i buy something new haha!!

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I have exactly this setup and have the diagonal after the filter. You will need an extension to the focus tube to get the filter into focus using an eyepiece. Then you will find that applying a diagonal there means mm of refocusing only.

I really didn't want the filter after a diagonal as it would be a lot of leverage if there is any slop. The weak point in any of this is The poor focuser on a st80 which provides little critical focus and a lot of slip unless tied down hard. All my couplings are m48 threaded and still I get some droop....

I now use an 80 ed at f/7 with microfocuser but there is still some slop...


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