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What is this


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Hi all.

While doing a star test I noticed a circle on the defocused star , I change ep's as I thought I had a mark on it but still the same. 

I never noticed it before any ideas .

Dave

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6 minutes ago, DaveL59 said:

The central dot or the wee one to the edge of it?

First would be the secondary, other maybe internal reflection somewhere?

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9 minutes ago, Captain Scarlet said:

I reckon it’s a piece of dust somewhere near the eyepiece focal plane, ie sitting on one of the eyepiece lenses

I tried different ep's and still the same.

When the star drifted across the fov the dot stayed still 

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It looks like a perfectly in focus star with an airy disk around it.

Was anything in your line if site when viewing ?
Any unusual obstructions within the OTA ?
Any big blemishes/pollen/dirt on the optics ?

Just throwing ideas around, have not seen this before……
 

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It looks like your seeing was not great, I would be tempted to check on another night with hopefully better seeing, when the scope is well cooled and the collimation has been checked.

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1 minute ago, Peter Drew said:

It's a very disturbed extra focal image, this condition can produce all sorts of artefacts.  Were there any anomalies at best focus?    🙂

No anomalies at best focus just a sharp star.

I only got the scope out to do a collinmation check as trying to collimate it all day, wish I kept the scope out longer to help out with my question

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10 minutes ago, Peter Drew said:

It's a very disturbed extra focal image, this condition can produce all sorts of artefacts.  Were there any anomalies at best focus?    🙂

What causes a disturbed extra focal image

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