Weird Diffraction spikes

[pook]

I've had enough. I've just mailed Stockport Telescope and Binocular Centre to ask for a replacement scope.

No one else with the same scope gets it, so mine has a problem so far as I'm concerned.

here's a copy of the mail I sent them.

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Hi,

I bought a SW 150P from you a couple of months ago, and I've been struggling to find an answer to a problem I've been having with it. When viewing objects, everything seems fine, but when imaging with the scope there are some weird diffraction patterns evident on the image. Please see the attached JPEG.

I've been trying everything I can think of with the help of some pretty knowledgeable people on the Stagazers Lounge forums, and everyone, me included is of the opinion that the mirror clips are the cause if this problem.

If this was something this particular scope suffered from, and was widely accepted knowledge I'd be happy to accept that's what happens when you build a scope to a budget price, but so many others with the same scope do NOT get this problem it makes me believe there is something particular with THIS scope that's not right.

Things checked so far.

Collimation. Checked with a cheshire, a laser, and a barlowed laser. All three methods confirm collimation is fine. A star test backs this up, with perfect rings each side of focus.

Pinched optics: I've even completely removed the locking bolts from the mirror cell to negate this being a reason.. plus the star tests confirm there is no pinching taking place.

Off axis light sources: I've imaged from some fairly dark sites now, with no local light sources and the results are the same.

Here's the thread I started on SGL. http://stargazerslounge.com/imaging-image-processing-help-techniques/133245-weird-diffraction-spikes-2.html

There's also another thread Discussing my scope here...

http://stargazerslounge.com/equipment-help/138623-10-inch-dob-help-me-decide-oo-vs-skywatcher-2.html

The general consensus seems to be that everyone else with a SW150p does not get the problem I do.

I'm just not at all happy with this scope. Is there any way I can exchange it for another one? I appreciate that it's been a few months since purchase, but it's taken me this long to rule out all the other possibilities. If we had a clear night every night it wouldn't have taken so long.

Thanks

David Gregory.

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I think that's reasonable. We'll see how they respond soon enough I suppose. I'm not expecting much; I don't have a great deal of faith in retailers when it comes to them replacing or refunding faulty goods. They all seem to try and pass the buck onto the manufacturer, even though the law clearly states that is is incumbent upon the vendor to replace faulty goods.

Not happy.

[pook]

Tony from Stockport Telescope and Binocular Centre has kindly offered to check the scope out, so hopefully this will be resolved soon

Peter.. in your opinion, how much would the clips need to be rounded to remove this problem? I'm just wondering how other identical scopes can not have this. Is it as fine as just smoothing the corners of the clips ever so slightly, or seriously changing the shape overall?

If it is literally just smoothing the edges then perhaps the tolerances in the manufacture of the clips are causing variation in the scopes. If that's the case, I'm surprised Synta haven't done something about it.

[pook]

UPDATE:

Scope changed for a new one. Will report back when I've taken some images with it.

[pook]

New scope.

That's better.

Just some patterning from the draw tube being so far inside the OTA for prime focus. This appears to look very much like Mike's now.

Here's the old one on the same star.

Big improvement.

[MikeWilson]

Much better.

Do you see what might be different? Was it the mirror clips?

[pook]

Nope. Physically it's identical. My money is on a bad mirror in some way or another.

[Digz]

Glad it all seems to be resolved and you are happy with the replacement

[MikeWilson]

I do still get a mild version of these diffraction patterns - I've got some Protostar flocking paper on the way and I plan to cut out little squares to cover the mirror clips as well as flocking the area around the primary mirror and at the front of the tube and around the secondary mirror glass.

[pook]

I think I'll still round off and reduce the clips as well... and possible baffle the outside couple of mm of mirror.