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I was getting some very ugly lopsided diffraction spikes on my f/3.9 Newt, and after a few hours of investigation and tweaking, it is now much, much better. (Long story short... pinched optics, collimation, mirror clip spikes, and focuser tube in light path).
Anyway, I now have a different issue. While not horrible, it's odd.

The difraction spikes are very clean and symetrical, but some stars on the left side of the image have an extra diagonal spike. It only happens to stars on the left side of an image, and it's either there, or not at all.

As an example, here is a quick 10m stack I captured of M45 this morning just before the sun came up.
I'm stumped.

Hi,

a couple of ideas...

Take the camera out and look through the telescope to see if there is something diagonal that shadows the sensor but only on one side.

Turn the camera through 180 degrees - if the spikes move to the right then whatever is doing it is in the telescope itself, if they stay on the left then the thing rotated with the camera.

cheers,

Robin

What's really weird, is that there isn't a defining line as far as left/right or top/bottom. If you notice in that second image there is a star without the diagonal spike to the left of the top one that does have it. It may have a small amount of it buried in the nebulosity, but if so it isn't much. The two smaller stars at the bottom left also don't show it.

I saw it in a couple of other images I captured last night also. It seems to be random, but always somewhere towards the left.

admin wrote: ↑Sun Aug 07, 2022 1:30 pm Turn the camera through 180 degrees - if the spikes move to the right then whatever is doing it is in the telescope itself, if they stay on the left then the thing rotated with the camera.

Robin,

Wouldn't this be backwards?

We are in cloud and rain now so I can't do any more testing, but I would think if the rogue spike moves with the camera rotation, then there is something related to the camera causing it... not the other way around?

Regardless, I can't see anything obvious in the optical path that would be causing it, and the fact that it happens to stars in between others without it, and independent of star brightness or size... is the real mystery.

Hi,

things attached to the camera itself (sensor glass, filters, etc) will rotate with the camera if you turn the camera, so anything there will appear to stay stationary relative to the camera field of view. Stuff in the telescope will appear to rotate as you turn the camera - if you turn the camera by 45 degrees you will see what I mean since the star spikes which come from the secondary mirror supports will turn through 45 degrees in the image.

Cheers,

Robin

Oh... I got ya. I was having a brainfart moment.