I have centre spotted my primary, and aligned it with a cheshire, but I would interested to know what every one thinks of this image i have stacked of canopus.
I am assuming the flaring to the bottom right would indicate collimation issues.
How did you take the image Dave ? Just the Toucam , no ep ?
The double horizontal diffraction spikes, is that from stacking several images ?
Have you checked for pinched mirrors, both primary and secondary ?
This was an early version before collimation basically out of the box, I have since centre spotted, and done up the screws holding the primary only finger tight .
Image was taken with a toucam and stacked in registax,
I will retake an image and have the "after" image.
The double defraction spikes indicate that the spider vanes in one direction aren't quite aligned together (I have the same with my 12.5" dob). The below diagram (loose use of the word ) may help you understand. It is a top view of your tube looking down on the spider vanes:
ie
..............|
..............|
....(------O______) <- notice the offset of opposing vanes
..............|
..............|
..............^ -Fine this way
If you can't understand the diagram I get back to me. To see if this is the thing that is creating your double diffraction spike you can just look along the line of the spider vane and you should be able to pick the miss-alignment. If it is...how do you fix it? If you spider is completely adjustable you should be able to "twist it out" through adjustments, however if the spider vanes are fixed (like my dob ) then you just have to live with them or replace your spider (as I eventually will....one day )
You can do the check anytime - remember you don't have to look through the telescope, just "eyeball" the alignment of your spider vanes from the top of your scope. I have attached a picture I just took of my upper cage assembly that shows the offset in the oposing spider vanes (in the directions of the arrows). It is subtle in the photo, but is more noticable in person. If you extend one of the spider vanes past the centre with an imaginary line you can see that the extension doesn't overlay the opposing vane. You can also notice from the picture that I have no flexibility in adjusting these vanes, so eventually I will replace them (possibly with a curved vane).
This tells me the spider is not made correctly (on Daves scope) Theres no way to fix that, that I can think of? Is there a warranty issue raising it's ugly head here?
I think that Dave's scope's spider will be way more adjustable than mine , but those with GS dobs will be better able to answer that. I only notice the double defraction spikes on the brightest stars so it may not be a big issue.
Davo, I'm not sure if it's just the angle/position that you took the pic from, but the top left/right of focuser, spider, looks slightly 'curved' to me. I put a rule against the monitor,(flat), & it lines up with the B/left to T/right, but not with the other 2. Could be just the angle.
I get a similar thing with mine, just out of focus. When in focus it's gone. So I use it as a guide sometimes. Helps to have an electric focuser tho.
HTH. L.
Hehehe! I did the same thing Laurie! With the ruler I mean...The 2 near vertical vanes in the pic look curved, yeah, but also one looks 1/2 a vane thickness not aligned with the other If you know what I mean to me ?
![[1ponders]'s Avatar](../vbiis/customavatars/avatar45_9.gif){kind=avatar}
) may help you understand. It is a top view of your tube looking down on the spider vanes:
L.
