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APM or Delos??


Paul73

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On 27/03/2020 at 12:57, Paul73 said:

Thanks Don

So I focus using the Paracorr rather than the focuser? Sorry about the blindingly basic question, but I’ve only ever found the need for one with wide wide angle eyepieces which i’ve only owned at the long end of things.

I’m sure that I’ve got an in travel adapter from when I had a set of Delos back when there were a few more ££ available for Astro gear.

Paul

 

Sorry, just saw your question.  The Paracorr's top is not smooth enough to be used for fine focusing.  What you do is focus with it (after setting the Paracorr with an eyepiece that you know the setting for and focusing the scope) when you insert eyepiece B just to find out what the proper setting is for eyepiece B.  Write it down.  Next time, before inserting that eyepiece, dial the top to the setting you discovered, then insert the eyepiece.  It'll be really close to focus and only a tiny touch up of the fine focus knob will be necessary to achieve pinpoint focus.  Even with knowing the settings for every eyepiece in your collection, you will still need about a 1mm range of focus in your focuser.

As for figuring out what eyepiece to start with, if you own a Paracorr 1, you should not use a 31mm Nagler, or 21mm or 17mm Ethos or a 20mm ES 100° as your starter eyepiece, as these do not have optimum settings in the range of the tunable top.

Use another eyepiece you know the setting for.  The eyepieces I mention will all use Setting 5 (all the way down on the Paracorr 1 ), but that setting is still a tad short of optimum.  Because they are not at the optimum position relative to the CC lens, if you focused using the tunable top on another eyepiece, it, too, would be at the wrong position for optimum correction.

So, an 8mm Delos uses the Paracorr 1.25" included adapter and the 14mm and 17.3mm use the in-travel adapter to make them parfocal with the 12mm and shorter Delos, all of which are parfocal.

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