Secondary mirror too low (Heritage 130p)

[a6400]

Hi,

Got cheap scope, Heritage 130p with awful focuser and spider vane but it gives nice views of the moon.
Just got a cheshire and decided to collimate it.

After attaching cheshire and blocking primary mirror from view, the secondary mirror seems too low.

Does it mean I should play with tilt screws?

This scope has weird spider, if I loosen the spider it will I believe push the secondary further but then it's too easy for it to rotate by simply touching it, so I screwed it in as hard as possible.

Images:
https://imgur.com/a/gvRsROl

Thanks!

[NGC 1502]

“Secondary too low” could mean several things.

“Too low” could mean it’s closer to the primary mirror than it should be.  Or it could mean not central within the optical path…..or…?
 

Not trying to be picky.  Using a Cheshire, the secondary should appear centred, exactly in line with the focuser.

[a6400]

I can’t get it right no matter what, perhaps someone with the same telescope could post a photo of their secondary and spider vane?

 

[a6400]

I have managed to make the secondary take most FOV in cheshire but more like 85%.

Also when I move primary the donut never moves, totally confused lol

[happy-kat]

I haven't a photo to hand of mine, the secondary vane is straight and horizontal, it's not bent or saggy.

[bosun21]

Hold your phone over the Cheshire sight hole and snap a photo or two. When you adjust the centre screw on the secondary you always have to adjust the tilt screws to compensate for moving the mirror up or down the tube.

[Rallemikken]

3 hours ago, a6400 said:

After attaching cheshire and blocking primary mirror from view, the secondary mirror seems too low.

Start with the focuser itself. If someone has taken it out, perhaps during flocking, it's a chance that it's not aligned right. Best way to check is by taking out the spider, and use a cheshire (or laser), and see if the line of sight is 90 degrees to the main tube, and no sideways tilt. Use a ruler and a permanent marker.

If the secondary is slightly high or low does not matter, as long as the scope as a whole is collimated and the usable lightbeam from the primary dont reach the edge of the secondary. But if the drawtude/focuser is misaligned, it will cause severe artefacts on the stars that you don't expect from even a little error.

Edited August 2 by Rallemikken

[a6400]

1 hour ago, happy-kat said:

I haven't a photo to hand of mine, the secondary vane is straight and horizontal, it's not bent or saggy.

This is how it looks like in my case, do yours looks similar? It also doesn't seem bend to me.

https://imgur.com/a/5Zl90yG

[a6400]

1 hour ago, bosun21 said:

Hold your phone over the Cheshire sight hole and snap a photo or two. When you adjust the centre screw on the secondary you always have to adjust the tilt screws to compensate for moving the mirror up or down the tube.

I did unscrew them all and screwed in the middle main one a lot, then screwed in tilt screws, there isn't much space left so not sure if it should be like that, last photo:

https://imgur.com/a/5Zl90yG

[a6400]

53 minutes ago, Rallemikken said:

Start with the focuser itself. If someone has taken it out, perhaps during flocking, it's a chance that it's not aligned right. Best way to check is by taking out the spider, and use a cheshire (or laser), and see if the line of sight is 90 degrees to the main tube, and no sideways tilt. Use a ruler and a permanent marker.

If the secondary is slightly high or low does not matter, as long as the scope as a whole is collimated and the usable lightbeam from the primary dont reach the edge of the secondary. But if the drawtude/focuser is misaligned, it will cause severe artefacts on the stars that you don't expect from even a little error.

It's a crappy plastic focuser which you can't really remove.

[Rallemikken]

18 minutes ago, a6400 said:

It's a crappy plastic focuser which you can't really remove.

If it's never been out, it most likely points straight down. But look for adjustment screws between the focuser's base and the focuser itself in case it's divided in two parts. Anyway, if it's not straight and no adjustment possible you can correct any error with spacers.

Maybe not relevant here, but when you are collimating a newtonian for imaging, the direction of the focuser is where you start if you suspect something is wrong. It's one of those things you do only once, or each time you have it out.

[happy-kat]

A wind or two of something like PTFE tape around the focuser can remove any slop if you find your focuser has some.