Have I broken my Scope?

[Velikovsky]

Hi All

I've been having imaging issues that maybe someone has seen before? If anyone knows whats up I'd be grateful for advice. Basically, I've been messing with my scope and I've started getting triangular stars. Here's a quick history.

Scope is a 6inch Skywatcher newt, bought ages ago (10+ years?) and EOS 500D camera. Focus done with a banitov mask.

1. Last Nov was getting good pics, round stars, fairly clear nebula etc, but I had to use a barlow if I wanted to use any filters because prime focus is right at the bottom of the focusser travel. Colimation was a pain too since it has the 3 little grub screws to adjust the mirror which is almost impossible in the field.

2. I decided to do a little mod over xmas and replace the grub screws with longer screws, springs, and thumb wheels to allow easier colimation and move the mirror up the tube half an inch to allow room for filters. I'm not too shabby with mechanics and the job was fairly easy, and I had a clean space to do it.

3. As we all know, over xmas was a wash out for observing so I tried a couple of terestrial shots, and imaged a led torch at the end of the garden 30mtrs or so and pics looked great.

4. First night out with the modded scope I get image aterfacts around the side of the image - star washed out in a fan away rom the centre, amd zooming on the images I see triangular stars.

5. First thought was ok, you moved the primary mirror too far up the scope, and you are seeing effects from the edge of the secondary or something, so I altered the mod, took out the springs and put in rubber washers which would give enough play to colimate. At this, the mirror was only about 1/4 inch farther down the tube from its manufactured position.

6. Next clear night (tonight) I try the scope and I still get triangular stars. Getting grumpy now, I had time and space so I reset the mirror mount to the original screws, grubs and little rubber buffers so its factory spec. Colimated with much effort (I have a laser colimator btw) pointed the scope at anything and bang, triangular stars again.

7. Now I'm here, probably should have come sooner, can anyone help?

Images are single pics, havent bothered to stack what I got (would only see cleaner triangles).

I recolimated a few times, tried shorter, longer exposures, with or without Mr barlow, and still same. What have I missed plz? Anyone?

Many thx in advance

Steve

[Velikovsky]

It just occured to me after posting this, Thinking where triangles might come from... maybe I've over tightenned the mirror and distorted it? I cant imagine I have, Its really just soft rubber clamps, but its the only triangle I can think of...

Steve

[cantab]

The first shot looks like coma. If it's in the middle of the field your collimation is out, if it's only round the edges and things are fine in the middle that's normal. The second I'm not sure on.

[Peter Drew]

Looks most likely to be collimation error, worth checking that the mirror is not tight as well.

[Velikovsky]

Hey all

Ok so I'm an idiot, the mirror was over tightenned. In my defence it is a very thin mirror, and the clamps are rubber, and they werent that tight. But I loosened it off so it was 'just' held by the clamps and everything is fine again.

Heh, another lesson learned.

Steve