Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Focuser rotator not aligned with optical train?

  • Please log in to reply
7 replies to this topic

#1 Pelayo

Pelayo

    Mariner 2

  • -----
  • topic starter
  • Posts: 254
  • Joined: 05 Jan 2019
  • Loc: Spain

Posted 14 September 2021 - 07:35 PM

In recent months I experienced some tilt in my images which I blame different things on. Finally I'm getting results I'm happy with after adjusting the backfocus as best as I could. There are some differences between corners but honestly I do not care.

 

However, today I superimposed images of the same object taken in different nights with slightly different angles. 

 

focuser tilt.png

 

Well, the center of rotation is not where I was expecting it!! It is displaced to the bottom. I made sure the rotator was secured and tight. I feel no wobbling in the draw tube of the focuser, or at least I don't think so. If anyone has an idea of what could be causing this, thank you in advance!

 

Edit:

Bottom corners, starts are elongated towards the center.

Upper corners, stars are tangential to the center.

 

As stated, I'm happy with the current look of my frames, however I feel curious about this.


Edited by Pelayo, 14 September 2021 - 07:40 PM.


#2 Oort Cloud

Oort Cloud

    Viking 1

  • -----
  • Posts: 994
  • Joined: 19 Nov 2020
  • Loc: New Jersey, USA

Posted 15 September 2021 - 12:00 AM

I have the same thing on my Z73...jist noticed it the other night because I swapped scopes and while setting the rotation, I inadvertently left the camera taking 5s shots...when I returned to the preview I saw a big swirl of stars and the center of rotation was nowhere near the center of the frame.

#3 Madratter

Madratter

    Voyager 1

  • *****
  • Posts: 13,238
  • Joined: 14 Jan 2013

Posted 15 September 2021 - 06:55 PM

It isn't unusual for scopes to have their optical axis in a different place than the mechanical axis. Or it could be that one mechanical axis is offset from another mechanical axis. And it does play hob. For example various collimation procedures assume optical and mechanical axis are aligned. Does your rotator have screws that adjust the tilt of the unit. If that is tilted instead of square it will cause this sort of thing.


Edited by Madratter, 15 September 2021 - 06:56 PM.


#4 Oort Cloud

Oort Cloud

    Viking 1

  • -----
  • Posts: 994
  • Joined: 19 Nov 2020
  • Loc: New Jersey, USA

Posted 15 September 2021 - 10:49 PM

It isn't unusual for scopes to have their optical axis in a different place than the mechanical axis. Or it could be that one mechanical axis is offset from another mechanical axis. And it does play hob. For example various collimation procedures assume optical and mechanical axis are aligned. Does your rotator have screws that adjust the tilt of the unit. If that is tilted instead of square it will cause this sort of thing.


Not sure, the rotator is built into the flattener. There are screws, but I haven't messed with it because I didn't want to risk having one of the lenses getting loose. The documentation from WO on what all the screws do on the focuser and flattener leaves alot (everything, basically) to be desired.

#5 Madratter

Madratter

    Voyager 1

  • *****
  • Posts: 13,238
  • Joined: 14 Jan 2013

Posted 16 September 2021 - 07:20 AM

Oort Cloud, I tried to find your flattener. I think this is it:

 

https://optcorp.com/...1UaAvw1EALw_wcB

 

If so, then I don't believe it can adjust the tilt of the rotation.

 

One fairly common source of minor tilt is the use of compression fittings. Other problems can cause this as well. For example, if the camera sensor is not exactly aligned with the center of rotation for the rotator it would cause this.



#6 Oort Cloud

Oort Cloud

    Viking 1

  • -----
  • Posts: 994
  • Joined: 19 Nov 2020
  • Loc: New Jersey, USA

Posted 16 September 2021 - 01:45 PM

Oort Cloud, I tried to find your flattener. I think this is it:

https://optcorp.com/...1UaAvw1EALw_wcB

If so, then I don't believe it can adjust the tilt of the rotation.

One fairly common source of minor tilt is the use of compression fittings. Other problems can cause this as well. For example, if the camera sensor is not exactly aligned with the center of rotation for the rotator it would cause this.


That is my flattener! No compression fittings, everything is threaded. I suspect the issue is the "adjustable" part of the flattener. The lock ring doesn't impress me. I may try to find a 2mm spacer to put behind and close it all the way. Its supposed to be set to 1.6mm for this scope, but my 2mm thick filters mean it should be 2.3mm

#7 Pelayo

Pelayo

    Mariner 2

  • -----
  • topic starter
  • Posts: 254
  • Joined: 05 Jan 2019
  • Loc: Spain

Posted 17 September 2021 - 11:52 AM

It isn't unusual for scopes to have their optical axis in a different place than the mechanical axis. Or it could be that one mechanical axis is offset from another mechanical axis. And it does play hob. For example various collimation procedures assume optical and mechanical axis are aligned. Does your rotator have screws that adjust the tilt of the unit. If that is tilted instead of square it will cause this sort of thing.

This is mine.

 

focuser.PNG

 

With the screws I have highlighted I should be able to adjust the resistance of the rotator, but also possible tilt problems? There are three of them spaced at 120ยบ.

 

I see no vignetting with the flattener-reducer I have, but there is some with the 1.0x flattener and this offset is evident too on the flats: As I have a flat panel, I could adjust comfortably during daylight the tilt on the rotator. Providing those screws are the ones to touch!


Edited by Pelayo, 17 September 2021 - 11:52 AM.


#8 Pelayo

Pelayo

    Mariner 2

  • -----
  • topic starter
  • Posts: 254
  • Joined: 05 Jan 2019
  • Loc: Spain

Posted 09 October 2021 - 07:57 AM

I did some tests with a dial gauge and during a complete rotation there was tilt at the edge of the draw tube. -10 / +20 hundreds of a millimetre during the rotation; Dial marked 0 at the start and the end of the rotation, so the measure was reliable. I was able to reduce it to 0/+5 hundreds adjusting the bolt which controls the mesh of the rack and pinion. It seems I had over tighten it in the past. I reduced the tension and still it does not wobble, so it looks just fine.

 

Next week I'm doing a test in the dark, we'll see the small problems I have at some corners of the field are gone.

 

reloj.jpg




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics