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I recently got a Celestron Omni XLT 150 Newtonian reflector telescope and it came with a 25mm eyepiece and whenever I've tried using it all I see is a dark center with a faint white light surrounding it. I've pointed it at Mars, Jupiter, and several stars and this is all I see. I've also collimated it so am I doing something wrong or is something wrong with the telescope or eyepiece?

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Not 100% about yours but the FLO website says they are fitted with a 2"/1.25" focuser. THat means there will be a 2" eyepiece holder in the focuser and there is very likely a 1.25" eye piece adaptor inside the 2" one. I say not sure as the Celestron site doesn't say anything.

If so you need to take both put and put back in only the 1.25" adaptor. That way the eyepiece is at the focal plane of the mirror and the shadow of the secondary should disappear. The 2 adaptors are designed to fit inside each other for shipping in the scope. If there are 2 adaptors in the focuser then the 1.25" eyepiece will be held too far out.

Someone did a neat design on the pair but it causes a lot of problems as when you receive the scope everything appears correct.

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Here I am guessing: Take out the 1.25" eyepiece and see if what it slides into is seperate to the focuser assembly and will pull (slide) out of the focuser. It may come out as just the 1.25" adaptor or if 2 in there both might come out. If there are 2 bits then you replace only the one for 1.25" eyepieces and keep the other safe somewhere. They really need to colour code the 2 bits, then it might be easy - pull out the Red 1.25" adaptor, pull out the Blue 2" adaptor and put only the Red 1.25" adaptor into the focuser.

In case the focuser is machined for 1.25" only just be a bit careful when pulling on it.

This occurs often on the Skywatcher 200P's but the Celestron site says nothing whereas the FLO site says fitted with a 2"/1.25" focuser. So if your has this dual size one there has to be adaptors for the different size eyepieces.

What makes it difficult is that it half reads that the dual fitting focuser may be a recent addition, so not sure what you may have. It will be a case of remove eyepiece, look and gently investigate.

The FLO site says:

Now fitted with 1.25/2-inch Crayford focuser.

The "Now" implies it wasn't at some time.

Check for any thumb screws that may be holding the adaptors in place, I would expect the adaptors tp be a push fit however, but there might be one, or three. Usually one and that is just to hold the adaptors in place. Similar to the one that hold the eyepiece in.

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What you are seeing is a 'doughnut'.

As you focus each star/planet goes from effectively an image of the open end of the scope - a circle of light around the 'dot' of the secondary mirror - to a tight dot image when in focus and then back to a 'doughnut'.

You may be surprised how far you have to wind the focuser in or out to achieve focus. I got caught out my first time with a Crayford focuser as if the lock (the knob at the bottom of your picture) is wound in the knobs will turn but the focuser won't move. Make sure the focuser freely moves when you turn the knobs (it should have a few inches of travel)

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