Star artifacts

Giuseppe Passera

Good morning everybody

I have a skywatcher telescope, an ed 120 PRO which in my opinion provides good quality images compared to the cost it has. The only problem is that it produces a diffraction on bright stars apparently caused by the supports on which the lens is mounted.

The thing is definitely boring as it requires me to use tools like starspiksespro to mask the effect and I would sincerely like to be able to avoid it.

It's not like anybody can get a few things out of the wizard's hat. I am attaching an example of the effect.

Thank you

Giueppe

Giuseppe Passera

I reduced the effect on the central and right star a little.

I created two starmasks with GAME, convolution on the mask to reduce the effect, 

increased the brightness of the mask with HT, 

applied a couple of passes of MLT with 10 layers disabled the first 5. 

A little noise generator and a slight reduction of brightness with HT. 

This is the result.

Wade Hilmo

I'm not sure that your telescope is working properly.

As a refractor, it should have no diffraction spikes at all.  I have a 102mm ED Astro-Tech scope.  When I first bought it, it produced very similar effects (but I had 4 spikes, not 6).  The issue turned out to be that there were some screws in the lens cell that were too tight and were pinching the lens.

To correct the problem, I found 4 delrin screws radially placed in the lens cell.  I had to remove the retractable dew shield to find them.  I backed each on off a fraction of a turn, and the problem went away completely.

Before resorting to complicated processing to address this, I would suggest that you contact Sky Watcher to see if they have any suggestions.  I suspect that this is fixable, but (unless you are experienced working on telescopes) I would not suggest attempting a fix without talking to them first for guidance.

Giuseppe Passera

It's an old problem very common in SW, Are the spacers between the lens that creates that spikes. 

The problem is that the lens are collimated in origin and eliminating the spacres means recollimate the lens and this can be very problematic.I'm not able to do it and If I have too send the scope back to China....

A Possible solution , that I have to test, is to create a diaphragm slightly smaller in diameter than the part of the spacers that protruding from the cell.

So I will have and ED119 but I hope without the spikes...

In the meantime I was looking for a way to mitigate the problem via sw.

Thank you very much for your suggetions and comments.

Giuseppe

BlockHead

Yes, creating a mask that covers the offending diffractors will definitely solve the problem at the expense of a small amount of aperture. Just be certain the mask has a smooth and sharp edge to it. The masks that I have put on some RCs in order to take care of the turned-down edge actually had beveled knife edges (you could cut your skin in the inner edge if you were not careful). 

and thanks Wade for responding!

I really want this to be a *user* forum... not a blockhead blog.

-the Blockhead

Giuseppe Passera

Thank Adam you for the answer. I will try with a 3d printer.

Tanks also to Wade.

I'll let you know.

ciao

Giuseppe