Spikes with a refractor puzzle

[MattJenko]

Hi,

I have a 80mm refractor and my images are displaying distinctive diffraction spikes on my bright stars. With a DSLR, really bright stars were getting a double spike (top and bottom), but since moving to a mono CCD and some filters, I am getting the classic 4 prong spike on even less bright stars. I can't quite work it out. They are not massive bloom type spikes and are pretty inoffensive, but has anyone got any suggestions as to where they might be coming from?

Cheers

Matt

[Oddsocks]

Often caused by objective lens separator spacers between the individual lens elements, if you look into the objective lens you may see them protruding slightly into the light path around the outer edges.

If very annoying they can be eliminated by stopping down the lens slightly with an external diaphragm that is just big enough to obscure the spacers.

[lensman57]

That is normal, don't fuss over it. The type of diffraction you have shown is caused by the air spacing between the lens surfaces the more lens elements the more the diffraction spikes.

A.G

[sharkmelley]

That is normal, don't fuss over it. The type of diffraction you have shown is caused by the air spacing between the lens surfaces the more lens elements the more the diffraction spikes.

But why would it have that orthogonal directionality?

Mark

[Thalestris24]

Lens clips?

[ronin]

Spacers between the lens that are encroaching on the light path or there are 4 screws holdong the lens in place and hey are pinching the optics.

Most likely the first, although it tends to be 3, maybe SW use 4 on their lens.

Not a lot I think that can be done easily.

The "not easy" option is to (have) the lens removed and seperated, then the spacers reduced or repositioned and the lens reassembled and recollimated.

I think I would enquire about the strip, adjustment and rebuild option as it would drive me up the wall.

[sharkmelley]

You could try rotating the camera 45 degrees to see if the spikes remain orthogonal or become diagonal.

Mark

[wxsatuser]

Never ever had them with my 80ED and I have had the objective apart.

There is a spacer with raised bits but it does'nt seem to protude.

See if the locking ring is to tight, undo it and then redo so it just touches.

In mine there is nothing in there apart from the two elements and the spacer.

[MattJenko]

Thanks for the tips. I'll have a play around with some of the suggestions this week, seeing as the moon is washing most of the sky out and post back what I find.