Weird collimation...?

[DJVege]

Hi guys,

Slightly different question, so I thought I'd post a new thread.

I collimated my scope yesterday, and when I was showing my relatives Jupiter, I found the "out of focus" Jupiter wasn't a perfectly round, fuzzy bubble. I've attached an drawing to explain what I saw. On the left you have what good "out of focus" collimation should look like (yes, I know I have no art skills and that it looks like a hairy eyeball ), and on the right is what I was seeing. However, when I focused, you could see Jupiter and the moons perfectly. Any explanation for this weird shape? Bad collimation?

Thanks guys. (and gals).

[Starkler (Geoff)]

It looks like something foreign is in the light path and blocking the eyepiece view of the full primary mirror.

Place your eye at the focuser tube and see if you can see the entire primary mirror reflected in the secondary.

• Is the secondary correctly aligned under the focuser to catch the full light cone of the primary?
• Is the focuser draw tube extending too far into the ota tube and intruding into the light path?

Another possibility is that the primary mirror mount clips are too tight, but if the chopped off part is really a straight edge this isnt the likely cause.

[matt]

Yeah. What Geoff said.

Also...were there any structures (buildings, etc) close to your line of sight when you were viewing?

[Phil]

i would say the secondary is not square with the focus er DJ.
Phil

[JohnG (John)]

I don't think your collimation is out at all. It looks to me like the light has been cut off by a building or something, the straight line is at the bottom of the image in real terms, Jupiter is getting lower at the moment, your focused image will still be fine even though there was a slight obstruction to the light path.

Did you try the scope on something closer to the Meridian and get the same effect ?

EDIT: That is based on your scope mentioned in your signature, 3 reflective surfaces put South to the top of what you see in the eyepiece.

Cheers

[DJVege]

Ah ok. Yeah, I get it now. I didn't think about that. It must've been the top of the house/gutter. I thought Jupiter was high enough to be viewed, which it was, but when out of focus (big blurry ball), the roof line must've cut the top off.

Thanks guys. Good to know the collimation is ok.