What's wrong with this picture?

[Allan]

The other thing you might want to check Morton are you spider vains. They don't look very parallel to me. The way I check is to grab a piece of cotton and hold it on either side of the tube where the vains attach to the tube. If the vains don't run exactly in line with the cotton across the whole diameter you will end up with 8 diffraction spikes instead of 4.

[RobF (Rob)]

Allan is right - the entire secondary assembly looks to be rotated with the vanes not converging at a single point - in the 3rd pic at least....

[AG Hybrid (Adrian)]

Looks like the price was way better for a reason. The spider veins dont even converge on the secondary properly. You didn't say what kind of scope it was?

[MortonH]

The spider vanes are now parallel but they seem to be offset on either side of centre by design. Can't remember if my previous scope was the same.

This one is a Saxon but it's the same as the Skywatcher model, both made by Synta to same spec.

I tried it out the other night and it seemed ok but the seeing was poor so I didn't use high enough power to notice any issue with the diffraction spikes. I'll check again when I can.

[raymo]

The spider vanes do converge correctly. The secondary holder has been
rotated by someone trying to loosen the centre screw. When the holder is back in its correct position the bottom two mirror adjusting screws will be
parallel to the vanes that are horizontal in the picture.
raymo

[MortonH]

Thanks Raymo. Will check that out later.

[MortonH]

Ok, so here are current pics after the adjustments of the other night. The secondary may not be perfectly positioned as I'm waiting for the replacement central bolt and then I'll do it more carefully.

However, I'm concerned with the comments about the spider vanes not converging to a single point. As you can see from the pics, there are four flat areas around the circular holder where the vanes attach. The vanes are screwed in and there is no way for them to move relative to the holder, nor does the holder itself rotate, so if the bottom two collimation screws aren't parallel with the vanes it must have been made that way.

None of the vanes seem to point directly at the centre of the hub. However I'm not sure if that matters? Do scopes with curved vanes meet in the middle? So isn't the important thing that they're parallel?

Just tested it on Canopus and there are two very close, parallel sets of diffraction spikes.

So are you saying the holes to attach the vanes to the secondary holder are in the wrong place?

[raymo]

You don't have a problem Morton, I have seen this many times over the
years. As I said, the secondary holder has been twisted to the left by someone trying to loosen the central screw. If you look carefully at your last picture you will see that none of the vanes is perpendicular to the
secondary holder. The top vane for instance leans to the left.
If you put two Allen keys in the bottom two mirror adjusting screws, [the horizontal ones]hold them in place with one hand, and put a screwdriver or something similar between them, and turn the secondary holder to the right until the vanes are at perfect right angles to each other. You will probably have to do it several times, as the vanes will try to spring back a bit from the position you stop in. Shouldn't take you more than a few minutes. As I said before, the bottom two screws should end up parallel to the horizontal vanes.
raymo

[MortonH]

Hmm, I'll need to be feeling brave to do that!

By the way, I used the scope tonight for several hours and it performed well. The diffraction spikes weren't an issue on Jupiter which showed good detail and contrast in average seeing conditions. Deep sky stuff was as good as it gets from my location.

So there's nothing badly wrong with the scope as it is. But when I get the new central screw I'll have a good look at sorting it out properly. What could possibly go wrong?

[raymo]

I'd happily do it for you, but you are 2,490 kays away. You'll find it quite
easy, all you're doing is the opposite of what caused the issue in the first place. You can alternatively remove, straighten, and refit the vanes one at a time. Just make sure that the foot of each vane that its two securing screws fit through is at exactly 90* to the rest of the vane.
Remember to have the tube pretty much horizontal, so no screws or tools can fall onto the primary mirror.
raymo