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D shaped stars sw 200pds


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Hi everyone

SkyWatcher 200pds with eos700d.

I think I've hit a similar issue which plagues the Skywatcher 130pds.

Symptom: D shaped stars on one side of the image.

Possible diagnosis: the focuser barrel is intruding into the light path.

Question: Could 200pds users shed any light upon this?

TIA

Focuser side:

s2.jpg.a3ac397e7ffe250ffef26afea6404e5c.jpg

Non focuser side:

s1.jpg.f329332b55e905ede099f41683232d8f.jpg

full size fits converted to jpg and view through cap:

NGC_5982_Light_001.thumb.jpg.484eeaf3cf999d4b1dd83a2955bf7608.jpgs3a.jpg.bf854932ed9b8d824d3a9a146bd32992.jpg

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  • alacant changed the title to D shaped stars sw 200pds

Hi everyone

I used a hacksaw to cut around 8mm from the focus barrel. No D shaped stars :)

Now the second issue: awful spikes around bright stars. Maybe I'm in the wrong section but Ill post the image here anyway. Particularly evident on the bright star toward bottom. All stars are affected to some extent and the spikes are always at the same angle and pattern no matter where they are in the frame. It looks awful!

The collimation is fine and I've darkened the edges of the secondary mirror. I loosened the primary clips. There are no obvious intrusions into the light path.

The thing that comes to mind are the primary mirror clips. Maybe cover them with a ring or remove them? Confusing because I would have thought the spikes would be at 120º corresponding to the spacing of the clips.

Any other ideas? 

TIA

m3: 700d on 200pds. 2x3min @ ISO800

1-3.thumb.jpg.101c7440c74ffbdd5c82a27f7d19ac91.jpg

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2 hours ago, bottletopburly said:

polyurethane sealant

Hi

That's a great idea. Just 'sealed' it. A decent blob on and to either side of the cork mirror supports.

My experience with SkyWatcher stuff is largely unprintable;) This was a lock down donation from a couple who were being flown back home in a hurry. Used only 2 or three times. Looks new. But what a mess!

If there are still spikes after this, I'm just gonna take a big hammer to it...

Cheers and thanks again for the idea.
ss3.jpg.f0e31134a11678c689a7a5dc1fc3c231.jpgss4.jpg.28f719467e369a9db89b057306acd54f.jpgss2.jpg.293e7065d9bbe2ea3c1d68c49ec9f7bb.jpg
 

 

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37 minutes ago, alacant said:

Hi

That's a great idea. Just 'sealed' it. A decent blob on and to either side of the cork mirror supports.

My experience with SkyWatcher stuff is largely unprintable;) This was a lock down donation from a couple who were being flown back home in a hurry. Used only 2 or three times. Looks new. But what a mess!

If there are still spikes after this, I'm just gonna take a big hammer to it...

Cheers and thanks again for the idea.
ss3.jpg.f0e31134a11678c689a7a5dc1fc3c231.jpgss4.jpg.28f719467e369a9db89b057306acd54f.jpgss2.jpg.293e7065d9bbe2ea3c1d68c49ec9f7bb.jpg
 

 

Nice gift ,

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21 hours ago, bottletopburly said:

Nice gift

I wish it were! 

OK, no clips and a sawn off focuser tube. Exactly the same awful spikes. Rotated the primary. exactly the same awful spikes.

So it has to be the secondary, right? Take out the 58mm secondary from the old 250p and place it in the pds. In the dark. Shining a torch to get collimated. Looked in the light of day and the secondary was way off centre. Anyway, managed 8x3 minute frames and hey, different -but still awful lopsided- spikes...

Here's hoping that with decent collimation, the spikes will at least get evenly radial.

Just called TS (the only place who do sw replacement parts it seems) €90 for a replacement secondary. Wonderful. Really fed up with this telescope.

Look at the spikes now. Still wrong...

Ahhgghh!

1746717776_3-3(copy).thumb.jpg.000a8ef5c924b89d49906d2d4d5c413e.jpg

 

Edited by alacant
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I don't think the quality of the primary mirror would have anything to do with the problem.  One remote possibility could be the secondary mirror being minimal size and the offset resulting in the light cone being clipped.  Would also be interesting to try another camera.     🙂🙂

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You can't be too critical to have such a superb image of a globular cluster.

As in: Spikes? What spikes? ;)

EDIT: Any shiny bits in the focuser drawtube or camera adapter tube?

 

Edited by Rusted
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1 hour ago, Peter Drew said:

secondary mirror being minimal size

Hi and thanks for your feedback. The secondary is 58mm and it looks as though it covers aps-c ok; there is minimal vignette.

1 hour ago, Peter Drew said:

try another camera

It's the same; 700d and 450d albeit more noise with the latter plus the 700d works spike free with both our ES reflectors, 250p and 130pds. Ok, there are spikes but not as pronounced and they are symmetrical.

Thanks again.

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1 hour ago, Rusted said:

too critical

Grrr...Maybe I am! It's just that using many reflectors over the years, I've never seen anything as bad and pronounced as this.

1 hour ago, Rusted said:

shiny bits

Yes. On the end of the focuser barrel where I cut it off to prevent it protruding into the light path.

Blacken it? 

Cheers

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Not sure if it will help

But after I have "circumcised" mine, - I used a black permanent marker to darken the place of the "injury"... And never had a problem... So cannot confirm...

But Aluminum is very reflective.... it must be it.

Edited by RolandKol
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If you haven't already done so, I would have a look at a bright star out of focus to see if there is anything missing from the diffraction disc.  If there is then the orientation will give a clue as to what is causing it.  I have only seen this effect through something encroaching into the light path.  Or a big chip off the primary or secondary mirror!     🙂

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2 hours ago, Peter Drew said:

something encroaching into the light path.

I wonder. When I change the secondary, the spikes change too. 

Gonna try the out of focus star too.

Thanks.

 

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21 hours ago, andrew s said:

star in the centre of the field

Hi. There are unsightly spikes no matter where the star is located in the frame. They are distorted by the cc toward the edge.

Thanks.

Edited by alacant
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27 minutes ago, alacant said:

I wonder. When I change the secondary, the spikes change too. 

Gonna try the out of focus star too.

Thanks.

 

Are the edges of the secondary blackened?  I would strongly suspect scattered light. I don't know this scope but I would look for and shiny surfaces in and around the tube  focuser, primary mirror cell etc.

Regards Andrew 

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45 minutes ago, andrew s said:

blackened

Hi. Yes. Blackened secondary edges and blackened main  tube. I also blackened the dawn off part of the focus tube. No mirror clips.

Running out of ideas!

Thanks.

 

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Thanks for that.  If that was an image of a star at the centre of the field then there doesn't appear to be anything obstructing the light path on axis.  An image taken with the star nearer to the edge would determine whether there is something off axis causing the problem.      🙂

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4 hours ago, Peter Drew said:

image taken with the star nearer to the edge

Hi

OK. Here is Vega out of focus left and right and in focus left-centre-right.

vega-izq1.thumb.jpg.b25b0502939cc2301cc8900ca25d1d11.jpgvega-izq.thumb.jpg.d30bc06cb499b42e1dbf1ca843a4aaaf.jpg

vega-dcha2.thumb.jpg.9dd24170b8f9c0433b1764d848c970e4.jpgvega-dcha1.thumb.jpg.60357cab1835863e8a0bf4ab376fe471.jpg

 

vega-izq.thumb.jpg.5ae5fd1409d2817d20887996c535ee07.jpg

 

 

 

 

 

 

 

vega-centro.thumb.jpg.0b64e98342ce89d661ca1b89519c7ec0.jpg

 

 

 

 

 

 

 

vega-dcha.thumb.jpg.0792b84e13016391f940b10ab8edcc3b.jpg

Edited by alacant
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