Weird stars again.

[emyliano2000]

Hi guys. Could this be a tilt in the focuser?

The first photo is a 5 min guided photo on a starfield near vega.

Second is vega perfectly centered.

Third is a crop of the bottom right corner.

 Fourth is vega centered and out of focus to check the collimation which as you can see is spot on. 

I was using a coma corrector and the distance was spot on.

Emil

 

[emyliano2000]

 

 Before I fitted the new focuser I measured and placed a mark exactly opposite to the center of the focuser hole. When the new focuser was in I checked it with the laser and it was centered to that mark.

After that I fixed the spider holder and centered it to the tube and I thought of inserting an allen key in the hole where the screw that's holding the secondary goes, to see if he laser is on it but it wasn't even close. I thought that shouldn't be a problem as long as the laser was pointing exactly to the mark opposite the focuser hole so I didn't look into it any furthet. Now I'm thinking that maybe, even if the spider holder is centered to the tube maybe it's not centered to the optical train and that's what causing the star shapes if you know what I mean.

The photo shows how it should be but the laser only goes on the allen key if the spider holder is not centered to the tube.

 

20180515_211213.mp4

 

 

[emyliano2000]

I took the focuser out again and rechecked it.

I also took the secondary out and this time I didn't center the spider holder by measuring each side. This time I looked through the hole where the screw holding the secondary goes and I moved the spider until I could see the doughnut on the primary and the reftection of my eye inside the doughnut.

Did the allen key test again and this time the laser beam had fallen on to it.

I hope this time it will be ok.

Emil

[emyliano2000]

Still not looking good ?

On the left hand side and on the bottom the stars look like they have a halo just at the bottom.

I really don't understand it. I checked everything.

[emyliano2000]

Could somebody translate these photos please.

is the tilt on the top right corner?

How should it look? Blue, like it is in the middle?

[Thalestris24]

Hiya

Yeah - looks like tilt somewhere... Can't really help with the CCD Inspector but I think you need an evenly populated starfield. There's a video here which might help.

I have to say, tilt problems were one reason I gave up on my 130pds which sits in the corner gathering dust... Refractors are sooo much easier to maintain though I miss the aperture of a Newt a bit. Our Rob / Uranium235 is an expert on tweaking his SW 130pds so may be able to give some helpful advice with your Newt if you ask him.

Louise

[emyliano2000]

Ok, there is definitely some tilt in the baader focuser and I couldn't solve it.

Because of that I decided to go back to the stock focuser and I am happy with the stars once again.

i will not give up on the fight with the baader focuser because it's a very good focuser. I must get the tilt sorted out. Could somebody please help me on this matter. What's the best way of getting rid of the focuser draw tube tilt?

Emil

[ollypenrice]

Are you sure the tilt is in the drawtube? Might it not be the entire body of the focuser which is not sitting correctly on the tube? I'm not sure of the best way to check the drawtube in the main body but maybe you could use a micrometer to measure the distance between the body and the thicker part of the drawtube at different points on its circumference. You could try this test with the drawtube in different positions of extension.

Or you could first find a perfectly flat surface checked with a good bubble level. Put the focuser on that, rack out the drawtube and put the level on the focuser. Rotate the level round to different angles and see if the bubble moves. That should be a fairly sensitive test.

I think you'll find a PDF instruction document on the Baader site.

Olly

[emyliano2000]

1 hour ago, ollypenrice said:

Are you sure the tilt is in the drawtube? Might it not be the entire body of the focuser which is not sitting correctly on the tube? I'm not sure of the best way to check the drawtube in the main body but maybe you could use a micrometer to measure the distance between the body and the thicker part of the drawtube at different points on its circumference. You could try this test with the drawtube in different positions of extension.

Or you could first find a perfectly flat surface checked with a good bubble level. Put the focuser on that, rack out the drawtube and put the level on the focuser. Rotate the level round to different angles and see if the bubble moves. That should be a fairly sensitive test.

I think you'll find a PDF instruction document on the Baader site.

Olly

When I fitted the focuser I made sure the base plate was level but after fixing it I put the level on the focuser tube and it wasn't level. I didn't take a photo of that because I lost all the appetite and packed them all up.

[emyliano2000]

1 hour ago, ollypenrice said:

I think you'll find a PDF instruction document on the Baader site.

Yes, I have them but how do I check if it's solved, taking test shots?

[alacant]

Hi. Do you have a Cheshire sight tube with cross-hairs? So long as you have the secondary somehere near central and the focuser bolted to the tube properly, setting the hairs central to the primary donut spot, any tilt will be taken out by the collimation process; it doesn't matter whether the focuser is aligned. HTH.

**the star test must be done at high magnification.I don't think 10x in apt is gonna hack it. 

[emyliano2000]

7 hours ago, alacant said:

Do you have a Cheshire sight tube with cross-hairs?

That's what I always use for collimation.

[david_taurus83]

Isn't the Baader adjustable? If you think the stock focuser is bang on can you not get some sort of slim straight edge to align down the sides of the drawtube and mark the profile onto the tube. Then refit the Baader and use the same method to align that drawtube to the axis of the original?

 

Eg: a steel engineering ruler aligned down the inside of the drawtube, on it's 4 cardinal points, and marking where the corner of the ruler meets the tube. Repeat then for the Baader and adjust until it's drawtube aligns with the stock.

[emyliano2000]

I though of a way to check if there's any tilt in the focuser drawtube.  In theory, if the baseplate of the focuser is "perfectly level", and once I put the focuser on to the baseplate, if the level on the focuser tube shows exactly the same measurements as it was showing on the baseplate, it means there's no tilt in the tube, right?

The first photo is on the baseplate and the second one on the focuser tube.

 

[geordie85]

19 minutes ago, emyliano2000 said:

I though of a way to check if there's any tilt in the focuser drawtube.  In theory, if the baseplate of the focuser is "perfectly level", and once I put the focuser on to the baseplate, if the level on the focuser tube shows exactly the same measurements as it was showing on the baseplate, it means there's no tilt in the tube, right?

The first photo is on the baseplate and the second one on the focuser tube.

 

Maybe you could try this on the draw tube once it's racked all the way out. Wouldn't that show tilt? 

[Thalestris24]

You might need something more accurate? I'm not sure what fraction of a degree would give rise to noticeable tilt - prob not very much...

Louise

[emyliano2000]

 

3 minutes ago, geordie85 said:

Maybe you could try this on the draw tube once it's racked all the way out. Wouldn't that show tilt? 

All the way out

[geordie85]

Sorry maybe I wasn't clear. I mean on the drawtube (circular bit) so it would show any tilt /slop as the weight of the camera may be causing it to sag/ droop down.

[david_taurus83]

The focuser might not have tilt in itself but there may be tilt in the optical axis once mounted on the scope..

[emyliano2000]

5 minutes ago, geordie85 said:

Sorry maybe I wasn't clear. I mean on the drawtube (circular bit) so it would show any tilt /slop as the weight of the camera may be causing it to sag/ droop down.

The focuser is made to take up to 6kg payload. I don't know if 500g would cause make it sag but who knows.

[emyliano2000]

4 minutes ago, david_taurus83 said:

The focuser might not have tilt in itself but there may be tilt in the optical axis once mounted on the scope..

It is possible. Isn't the method that I had shown earlier in the thread good enough to make sure it's not tilted in the optical axis?

[david_taurus83]

4 minutes ago, emyliano2000 said:

It is possible. Isn't the method that I had shown earlier in the thread good enough to make sure it's not tilted in the optical axis?

Yes, you've done a good job in making sure the focuser and OTA are perpendicular but that doesn't mean the light path is the same. Collimation should take care of that, but there's a difference in weight of collimation tools and then inserting cameras. In fact, you might have made the installation  TOO good. The stock focuser might be slightly off perpendicular but closer matching the optical axis. That's what I'd be trying to match as you seem to have gotten better results. Would be interesting to see if the stock focuser is also level on that flat surface and compare side by side.

[david_taurus83]

Also, have you tried putting the camera in the focuser as well and checking for level while your at it?

[emyliano2000]

2 minutes ago, david_taurus83 said:

Also, have you tried putting the camera in the focuser as well and checking for level while your at it?

I had to put them aside. Got work tomorrow ?

[Guest]

On 31/08/2018 at 11:04, emyliano2000 said:

When I fitted the focuser I made sure the base plate was level but after fixing it I put the level on the focuser tube and it wasn't level. I didn't take a photo of that because I lost all the appetite and packed them all up.

but did you test you spirit level for accuracy before doing this?