Is it my eyes or telescope?

[Kirby301]

hi all,

I want to start splitting double stars.

However, I've encountered something that may become a problem on my first star!

I have a skywatcher heritage 130p and I decided to split Almach. I used my standard 25mm and then my 8mm bst eyepiece.

I split it, but I had a spike coming off of the primary that was close to blocking the view of the companion star.

What causes this to happen?

The telescope is stored in the shed and is the first thing bought out to cool down.

The eyepieces are left with it to cool down.

 As I wanted to do double star work I know I needed to be accurate with my collimation, I followed the astrobaby collimation guide to a tee, i also collimated my laser collimator and checked it against my own collimation. I did a star test and with the star fully defocused I can see the 3 clips around the edge of the mirror the vein and the secondary mirror. Everything was centred and evenly spaced. I'm 99.9% accurately collimated.

The only other things I can think of is its either my eyes or maybe its not the best telescope for splitting doubles.

Any advice would be greatly appreciated.

Many thanks.

[Woj2007]

37 minutes ago, Kirby301 said:

 

I split it, but I had a spike coming off of the primary that was close to blocking the view of the companion star.

What causes this to happen?

 

Hi there,

Could be off-collimation, but if the scope is well-collimated, most probably it was a tube current. It happens to my views when I don't ventilate the tube, even when it is cooled down.

Do you have a fan on the rear of the tube?

Try the star test: if on one side of defocus the star image has a spike and on the other it is somehow flattened, that's the tube current. If the stars in and out of focus have spikes, than collimation is needed. 

You could also rotate the eyepiece and see what happens to the spike to eliminate eyepiece errors.

Finally, rotate your head. If the spike rotates too, that's your astigmatism.

 

 

[vlaiv]

1 hour ago, Kirby301 said:

I split it, but I had a spike coming off of the primary that was close to blocking the view of the companion star.

What causes this to happen?

You are using newtonian telescope and newtonian style telescopes have secondary mirror and what is more important in this particular case - secondary mirror spider support.

Most of them have either 3 or 4 vanes but sometimes, and I believe that heritage 130 is such - it has single secondary mirror stalk.

These cause diffraction spikes on bright stars and that is fact of life. Depending on a type of spider - you can get 2 spikes, 6 spikes, 4 spikes, etc ...

Explaining why that happens is rather complex topic, but here is what you should know - spikes happen perpendicularly to each vane you have on your support - hence if you have single stalk you'll have two spikes or rather single line across the bright star.

Now that we know how these spikes form - what can we do about them when observing double stars? Well, key is in sentence above - perpendicular to spike itself. Want to change spike direction so you can see companion star clearly? Change direction of secondary support - rotate your telescope a bit and spike will also rotate.

 

[CraigT82]

Thats the diffraction spike from the stalk holding the secondary mirror. There should actually be 2 spikes 180 degrees apart. Perfecrly normal. 

[RT65CB-SWL]

Diffraction spikes are 'normal' for Newtonian reflectors.

It's a crunchy/smooth peanut butter or Marmite thing... you either hate it or love it.

[johninderby]

This will help illustrate.

[Kirby301]

Thanks for everyone's help. After reading all the replies it seems it is obviously a diffraction spike from the single spider vane.