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Can't focus with 28mm - Brand New Skywatcher 200p


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Hi All,

I have made the leap yesterday from my starter and basic 70/700 to a 200/1200 skywatcher!

Am delighted as I should be.

Where I am looking for some help is the fact that I have set up the new beauty yesterday as the Heavens were kind and i had a beautiful sky.

However using the 2'' 28mm eyepiece that came with the tube, I was not able to achieve focus at all. Basically i saw nothing, not even big blobs out of focus. I then tested with a 17mm 1.25'' piece and that seemed fine.

Going back to the 28mm i found that when i barely insert the eyepiece i.e. it almost falls out, then I can get focus...

Would this mean that I need to collimate my mirrors or could there be some other issue?

I have attached what i see when using a collimating eyepiece.

post-41451-0-41103700-1423394647_thumb.j

Thanks a lot for the help in advance!

kryfo

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Let's ignore collimation for a bit here.

You need an extension tube to reach focus as you are running out of focuser travel. Most dobs/newts come with a 35mm extension to give you sufficient travel outwards to focus some eyepieces.

Your comment that if you pull out the 2" eyepiece to manage to reach focus confirms this. Hit your local astroshop or the forum's sponsors FLO for an extension tube.

Back to collimation: It apparently needs collimation, I.e. aligning the primary and secondary mirrors, but first let's resolve the focusing issue.

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Hi Nicos,

Thanks. So is this normal that a regular eyepiece needs an extra extension for it to be usable?

cheers

Each eyepiece will focus at a different point. Reflector focuses typically have a small range of travel as they cannot protrude into the optical hubs too much. Therefore thr easy solution is to preserve optical performance (I.e small travel distance) and optimise the focusser location on the OTA where you need more travel out to focus. Hence the extension.

The good news is that an extension tube is a fairly cheap accessory!

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