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2 hours ago, Spacehead said:

The single stray spike is my pet hate though - I mean its wrecking my life (lol) - are you saying that is also characteristic of sw newts?  Can you show me a pic displaying this problem from your 150?

Here you are. It's the only image affected by this artifact, luckily. 

It's on Electra. 

_20190515_122405.JPG

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6 hours ago, FaDG said:

Here you are. It's the only image affected by this artifact, luckily. 

It's on Electra. 

_20190515_122405.JPG

That is incredible the way cutting off the focal tube has got rid of the flaring - how utterly stupid a design is that????????  The mind boggles.
I can see your rogue diffraction spike too - if mine was in the outer region like yours rather than the middle of the image, I wouldnt bother with it.  But unfortunately mine is all over the place.


 

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Hi

extra star spikes you show going round in a circle are normally caused by a bright star bouncing off the edge off your secondary so black these up inc the small ground edge if you have one ( I suspect you have )

The extra spike is caused by the veins not being parallel to each other , do have to be straiht in line but parallel  so put a straight edge down each vein and check the opposite is completely parallel

with it .

this should remove your extra spike

Regards

Harry 

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1 hour ago, harry page said:

Hi

extra star spikes you show going round in a circle are normally caused by a bright star bouncing off the edge off your secondary so black these up inc the small ground edge if you have one ( I suspect you have )

The extra spike is caused by the veins not being parallel to each other , do have to be straiht in line but parallel  so put a straight edge down each vein and check the opposite is completely parallel

with it .

this should remove your extra spike

Regards

Harry 

I'd be hard pressed to get the spiders more parallel than they are already without some kind of laser guided scientific device to be fair.  They are all but hidden behind the yellow lines.
 

spider1.jpg

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Hi

agreed looks straight in line , then it means something else is in the light path- does your focuser stick out much ?

 

Harry

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1 minute ago, harry page said:

Hi

agreed looks straight in line , then it means something else is in the light path- does your focuser stick out much ?

 

Harry

Yes - it does indeed - check out the post above from F in italy (an earlier one than the one with the star pics of his).
In his post he says that the wide flaring is caused by the protrusion of the focuser so he cut his right back for astro photography.  Which is why his stars above show round with no flaring - but note the one at the top - has the same artifact as mine (except mine is in more positions than his).  This means (at a glance) - that the focuser is not the cause of the extra spike (given he has chopped his back - so has no flaring - but DOES have the extra spike).

 

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Posted (edited)
1 hour ago, Spacehead said:

In his post he says that the wide flaring is caused by the protrusion of the focuser so he cut his right back for astro photography

Yes, you're fully right. 

After chopping it off I did not have the hideous flare anymore. 

And this is what the reworked focuser looked like. 

_20190515_225807.JPG

Actually, the design is not flawed per se: you REALLY need the extra length in order to use the scope visually, just, when rectracting it all the way in, the end of it enters the light path. 

It's just another trade-off: to avoid it, Skywatcher should have used a MUCH larger tube for the 6". Hardly a better design choice. 

Even so, 90% of the users never complain and are super happy of their results. Not me!

But now I find it to be a great budget scope.

Yet, if you find the root cause of the weird spike, I'll be happy to deal with it too. 

Fabio

Edited by FaDG
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11 hours ago, FaDG said:

Yes, you're fully right. 

After chopping it off I did not have the hideous flare anymore. 

And this is what the reworked focuser looked like. 

_20190515_225807.JPG

Actually, the design is not flawed per se: you REALLY need the extra length in order to use the scope visually, just, when rectracting it all the way in, the end of it enters the light path. 

It's just another trade-off: to avoid it, Skywatcher should have used a MUCH larger tube for the 6". Hardly a better design choice. 

Even so, 90% of the users never complain and are super happy of their results. Not me!

But now I find it to be a great budget scope.

Yet, if you find the root cause of the weird spike, I'll be happy to deal with it too. 

Fabio

Hi Fabio, cheers for all the tips.  I might look into shortening the tube myself - not sure yet - I will have to measure up the webcam and my camera focus to see how "little" I can get away with.
If I ever sort out the spike - I will let you know - but its not looking like I will be able to.

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12 hours ago, FaDG said:

Actually, the design is not flawed per se: you REALLY need the extra length in order to use the scope visually, just, when rectracting it all the way in, the end of it enters the light path. 

There's another solution to this problem:

https://www.firstlightoptics.com/skywatcher-focusers/dual-speed-low-profile-1252-inch-crayford-focuser.html

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Posted (edited)

Jut to make things a bit more difficult...

In my case, focuser's protrusion did not look like that...

In fact, my diffraction spikes there only 4, but the stars were looking almost in the shape of letter "D" , - bitten off, as they been shadowed by the focuser...
 

No idea what causes that 5th spike... but I am almost sure, it is Not the focuser's draw tube...

P.S.
Focuser is parallel to one of the spider veins... if it would  be the cause, one diffraction spike would become much shorter (shadowed)...

Edited by RolandKol
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2 hours ago, wimvb said:

Yes, you're right. But considering that I fully solved that issue in less than half an hour, I'm now 129 pounds richer! 🙂

Seriously though: this was a friend's scope and it was a catastrophe, as the secondary was totally uncollimated and almost stuck to the point that one of the spider vanes bent when I tried to get it free, the primary strongly tensioned (almost triangular), the focuser was squinted, so the flare was really only the minor issue!

Actually I told him to sell the bloody thing for cheap, but then I tried messing with it and the Ugly Duckling became a wonderful Swan, as it had really great optics, just assembled by the wrong guy! Yet, when it finally was perfect my friend decided that a Newt was too complicated for him (a newbie) and asked me to keep it: I struggled to convince him even to accept some money (what I consider a low price for that value: I've been lucky on that). Hence, you see, there was really no sense in investing on it at the time.

 

Fabio

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2 hours ago, FaDG said:

Yes, you're right. But considering that I fully solved that issue in less than half an hour, I'm now 129 pounds richer! 🙂

Seriously though: this was a friend's scope and it was a catastrophe, as the secondary was totally uncollimated and almost stuck to the point that one of the spider vanes bent when I tried to get it free, the primary strongly tensioned (almost triangular), the focuser was squinted, so the flare was really only the minor issue!

Actually I told him to sell the bloody thing for cheap, but then I tried messing with it and the Ugly Duckling became a wonderful Swan, as it had really great optics, just assembled by the wrong guy! Yet, when it finally was perfect my friend decided that a Newt was too complicated for him (a newbie) and asked me to keep it: I struggled to convince him even to accept some money (what I consider a low price for that value: I've been lucky on that). Hence, you see, there was really no sense in investing on it at the time.

 

Fabio

Fabio, sounds like you got a deal as good as it can get.  What do you mean by these two things "the primary strongly tensioned (almost triangular), the focuser was squinted"?

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Just now, Spacehead said:

Fabio, sounds like you got a deal as good as it can get.  What do you mean by these two things "the primary strongly tensioned (almost triangular), the focuser was squinted"?

I mean that, out of the box, the scope was utterly unusable!

As you know, the primary mirror cell is held in place by three couple of screws. But these do not (thank God!) act on the mirror directly, as it is supported by three holders. Well, if these are screwed too tightly, they can deform the mirror, and this can be seen as a pattern diverging from the theoretical circle. In extreme cases (and mine was one of these) the deformation is such that the out of focus pattern acquires an almost triangular (curved, clearly) shape. So I removed the mirror from the cell, let it rest for three days, and reinserted it very carefully. Perfect circle!

squinted focuser: the SkyWatcher crayford has a set of screws which allow to tilt it: in my case this was needed because the camera sensor was not orthogonal to the light beam (stars in focus close to the centre and out of focus on the sides, intra on one and extra on the other)

Just for sake of completeness: the secondary shadow not being centred in the out of focus pattern is NOT a defect. the fast Newt design needs this for better field illumination.

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