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Spacehead

Is there a focus problem here?

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Spacehead    34

Hi All,

Here is a photo through my scope with the Bahtinov mask in place.

So when I am zeroing in on the focus, I will tend to zoom in on live view on the camera and try as best I can to ensure the middle spikes are dead centre (as far as my eye will discern) to the outer spikes.

The other night I ended up taking a picture with the mask still on (see below) - and when I zoom in on it - there seems to be double spikes.  Ive looked around the net but can't find another example of this.

Although my primary mirror donut and the eyepiece black circle are dead aligned on collimating, im concerned that good alignment of the donut and eyepiece dot could still be achieved IF the primary is tilted somehow - but the secondary is tilted to compensate?

Can anyone explain what is showing there in that image?  Cheers.
 

bmask.jpg

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Spacehead    34

Further thought on this, please see the image below.  Notice that the star's left side diffraction spike goes all the way to the edge whereas the right spike does not.  Im wondering again if a primary which was not at 90 degrees to the tube would stretch one side of the image (as in the spike) like that?
(I also have a split top spike - no idea what that is either!!)
 

actur.jpg

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Xplode    653

How long was the exposure? Seems just like the scope was bumped or something during the exposure.
The split top spike is your spider not being perfectly adjusted as a cross

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Spacehead    34

Xplode - you know Xplode, you might well be right there with a bump.  It was 9 seconds the exp.  So that means that there could have been a bit of a gust of breeze (it was on and off that night the breeze) but also - my cam is set to 1 minute, which means I will have grabbed the hand controller to press the stop button.  I bet thats the answer on the Bahtinov mask image.  Thanks for that - I will have to double check next time its clear but yup - Im confident that is all it is - thankyou.

On the split top diffraction spike on the star - do you reckon one arm is "twisted" - or do you mean that the four spider arms arent at a perfect 90 degrees to each other?  Ive been trying to solve that for about a year!!!

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