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130PDS Reflector Odd Star Shapes


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7 minutes ago, JamesAstro2002 said:

tilt in the foccuser

Or the Cheshire is making the focuser sag...  Or the Cheshire isn't square in the focuser... It's what sw focusers do.

Anyway, take the secondary up the tube -clockwise on the centre bolt of the spider- about 1/2 turn and recollimate with the Cheshire at the position you would normally focus. I wouldn't go any further until you have feedback from the camera frames.

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41 minutes ago, alacant said:

Or the Cheshire is making the focuser sag...  Or the Cheshire isn't square in the focuser... It's what sw focusers do.

Anyway, take the secondary up the tube -clockwise on the centre bolt of the spider- about 1/2 turn and recollimate with the Cheshire at the position you would normally focus. I wouldn't go any further until you have feedback from the camera frames.

Okay, thanks.

Does this look any better?

20190904_172301.thumb.jpg.0df2c81c058c397246dde376ce6c7fd4.jpg

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35 minutes ago, JamesAstro2002 said:

any better?

That will do, but since we're trying to sort out misshapen stars, maybe we could perfect it?

1/4 turn more on the secondary centre screw should have the secondary dead inline with the focuser. Whilst you have it loose, get those Cheshire cross hairs dead centre of the primary donut reflection; ATM they're at about 10 o'clock given the orientation of your photos. Now the easy -but most important- bit.; adjust the primary to coincide perfectly with those cross hairs.

But before we go over the top, let's take a while to read the common collimation myths.

How's the sky? Don't get it too perfect or the clouds are sure to roll in!

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28 minutes ago, alacant said:

That will do, but since we're trying to sort out misshapen stars, maybe we could perfect it?

1/4 turn more on the secondary centre screw should have the secondary dead inline with the focuser. Whilst you have it loose, get those Cheshire cross hairs dead centre of the primary donut reflection; ATM they're at about 10 o'clock given the orientation of your photos. Now the easy -but most important- bit.; adjust the primary to coincide perfectly with those cross hairs.

But before we go over the top, let's take a while to read the common collimation myths.

How's the sky? Don't get it too perfect or the clouds are sure to roll in!

Sure.

Okay, I've adjusted it again, this looks better to me, not sure if it's perfect..

 

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Hi

I don't think that's a star test. Rather a way out of focus star. What did the stars look like when in focus?

Anyway, it looks good. Concentric centre field and you can see the cc doing it's job toward the edge.

The cutoff is because the focuser tube is cutting into the light path. With the sw cc and a dslr, you'll need to cut off 13mm from the focuser tube. Remove the focuser and cut off the end of the focus barrel. No need to dismantle the focuser. It's soft metal and a fine toothed hacksaw will do the job easily.

Look at the focused stars; they should be good corner to corner, now limited only by the cc optics.

HTH

Edited by alacant
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Yeah I know. But the clouds rolled in quickly so I only had time to quickly look at polaris out of focus. I did briefly view the star in focus but it still looked to have that fringing on the edge, but the clouds soon rolled over so I couldn't tell properly.

I thought that the out of focus star test for collimation was supposed to look the same in the edges as it does the center ? It looks to me like the dark circle has shifted slightly when at the edge of the frame.

And I've already cut off some of the focusser, looks like it may need a little more cut off as you suggested, though.

Hopefully I'll get a longer patch of skies tonight so I can actually test the stars in focus. I just assumed that the out of focus star test looked bad at the edges - but we'll see.

Thanks for helping out :).

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Luckily enough, tonight is a decent clear night so I've been able to do a test run. Stars are looking nice and round all the way to the corners now, so you were correct, thanks a lot alacant! L_0003_ISO400_120s__20C_ABE.thumb.jpg.d032d39ebc42ba4670f8628c2d318286.jpg

Do you have any idea what that odd looking thing is under the bright star? I'm guessing some sort of reflection. Looks like I have a slightly twisted spider vane as well.

 

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8 hours ago, JamesAstro2002 said:

odd looking thing

Hi. The cc causes reflections. Cheap way out: don't include bright stars in your fov or just heal it away. To lose it completely and keep your stars into the corners you'll need the other sw cc. It would also focus further out and in so doing obviate the need for the hacksaw.

Cheers and well done for sticking at it:)

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3 hours ago, alacant said:

Hi. The cc causes reflections. Cheap way out: don't include bright stars in your fov or just heal it away. To lose it completely and keep your stars into the corners you'll need the other sw cc. It would also focus further out and in so doing obviate the need for the hacksaw.

Oh right, okay that makes sense.

4 hours ago, alacant said:

Cheers and well done for sticking at it:)

Thanks again for the help! Clear skies :)

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12 hours ago, JamesAstro2002 said:

Just gathered a few more test frames, that weird coloured blob seems to be moving across the frame?!

L_0009_ISO400_120s__20C_ABE.thumb.jpg.36cceb662c184cfc4e3506ce52c14c3a.jpg

Now another bright blob around Vega has just popped up! These are some nasty looking reflections, but I don't know what's causing them.

L_0009_ISO400_120s__20C.CR2 20.91 MB · 0 downloads

The next thing you will want ot do it to chop down that focuser tube to stop it heading into the light path!

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