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

Dent/Bump while focsuing

astrophotography beginner refractor dslr
  • Please log in to reply
15 replies to this topic

#1 Orangeray

Orangeray

    Lift Off

  • -----
  • topic starter
  • Posts: 16
  • Joined: 06 Jun 2019

Posted 02 June 2020 - 02:56 PM

Hey everyone

 

The last few weekends I was blessed with clear skies and finally got to test my new William Optics SpaceCat 51 APO 250mm f/4,9 together with the iOptron Skyguider. After a few nights out some questions came up. The first is related to the Telescope itself. When it arrived I put everything together and took a few test shoots and then put everything away. About a week later I used it again and while focusing, I could feel a "bump" everytime I'd arrive at my desired focus position. When I first got it and tried it out, I forgot to loosen the clutch on the focuser, maybe that's what caused this "dent"? Though I'd think that there's some sort of mechanism to tighten the Focus which is not putting pressure on a single point right?

 

The other question is related to Astrophotography in general. When balancing a mount which is only equipped with an RA-Axis (or at least only the RA-Axis is motor driven), do you guys set proper balance when the camera is aiming parallel to the axis or for the desired shooting position. In every video that I watched, the camera was looking parallel to the axis, but when I do it like that, the balance will only be good in that situation and as soon as I set it up for my target I can feel a lot of weight pushing against it. That question stuck with me since the beginning and since I got pretty bad tracking results in the last few nights I started wondering if that might be the cause?

 

And then my final question is related to the process of taking Flat Frames. It is said that Flat Frames should be taken in the same position as the imaging position. But which imaging position do I choose if I have a session that is 5/6 hours long, the mount travels quite a lot and changes the position. Until now I used to take them after imaging with the T-shirt method and in the dark. Since I'm using my Smartphone screen as Light source and I feel like this might not be enough, I would prefer to take them at the beginning of an imaging session, when it's still bright outside. So my question is, would a rough positioning of the telescope be enough for Flat Frames?

 

Thanks in advance and clear skies to you all!

 

Michael



#2 kathyastro

kathyastro

    Surveyor 1

  • *****
  • Posts: 1,830
  • Joined: 23 Dec 2016
  • Loc: Nova Scotia

Posted 02 June 2020 - 03:15 PM

I can't help you with the bump in the focuser.  It is possible that there is damage to the mechanism or maybe just a bit of dirt.

 

Declination is balanced in two directions: scope facing the pole, and scope horizontal.  RA should be balanced after dec is balanced (since balancing dec could affect the RA balance), and should be done with the counterweight arm horizontal.

 

The position of the scope for flats does not matter.  What must not change is the position of the camera relative to the scope.  You must not rotate or remove the camera between taking flats and lights, and you should avoid changing the focus.


  • arrowspace90 and Orangeray like this

#3 Orangeray

Orangeray

    Lift Off

  • -----
  • topic starter
  • Posts: 16
  • Joined: 06 Jun 2019

Posted 02 June 2020 - 03:34 PM

 

Declination is balanced in two directions: scope facing the pole, and scope horizontal.  RA should be balanced after dec is balanced (since balancing dec could affect the RA balance), and should be done with the counterweight arm horizontal.

Okay, so with my current setup I'm only able to balance out the RA then? It looks like this:

redcat-51-mounted-to-skyguider-rpo.jpg
 Or should I try to adjust the position of the scope so that it "feels" kinda balanced around the turning point?

 

 

The position of the scope for flats does not matter.  What must not change is the position of the camera relative to the scope.  You must not rotate or remove the camera between taking flats and lights, and you should avoid changing the focus.

Ohh okay, well that makes things a bit easier, thanks for the answer! :)



#4 kathyastro

kathyastro

    Surveyor 1

  • *****
  • Posts: 1,830
  • Joined: 23 Dec 2016
  • Loc: Nova Scotia

Posted 02 June 2020 - 05:10 PM

It looks like you have several inches of dovetail you can play with to balance dec lengthwise.  If you can’t balance it within that range, you might need a longer dovetail or an auxiliary counterweight.  You won’t need to balance dec laterally, since you have no asymmetric.  Since you have no dec motor, balancing dec is not critical.  I’d balance it anyway, just because I’m a little bit OCD.

 

Balancing RA is important to reduce strain on the motor.



#5 Orangeray

Orangeray

    Lift Off

  • -----
  • topic starter
  • Posts: 16
  • Joined: 06 Jun 2019

Posted 03 June 2020 - 02:13 AM

It looks like you have several inches of dovetail you can play with to balance dec lengthwise.  If you can’t balance it within that range, you might need a longer dovetail or an auxiliary counterweight.  You won’t need to balance dec laterally, since you have no asymmetric.  Since you have no dec motor, balancing dec is not critical.  I’d balance it anyway, just because I’m a little bit OCD.

 

Balancing RA is important to reduce strain on the motor.

Okay, so the orientation of my DEC will not affect the balance of my RA? I mean now that I think about it it's obvious that it won't, since there's the same force working on both ends, as long as the counter bar is horizontal. But as soon as I change the orientation to point at my target it will obviously start to try and get back into the horizontal position right?



#6 Rudix

Rudix

    Sputnik

  • -----
  • Posts: 28
  • Joined: 11 Feb 2019
  • Loc: South Africa

Posted 03 June 2020 - 08:02 AM

Okay, so the orientation of my DEC will not affect the balance of my RA? I mean now that I think about it it's obvious that it won't, since there's the same force working on both ends, as long as the counter bar is horizontal. But as soon as I change the orientation to point at my target it will obviously start to try and get back into the horizontal position right?

No, it should not, if it is balance it should stay in any position you leave it. Make sure you don't have cables causing drag or binding.


  • Orangeray likes this

#7 Orangeray

Orangeray

    Lift Off

  • -----
  • topic starter
  • Posts: 16
  • Joined: 06 Jun 2019

Posted 03 June 2020 - 08:21 AM

No, it should not, if it is balance it should stay in any position you leave it. Make sure you don't have cables causing drag or binding.

Hmm that's strange, When I have my camera in a neutral position (parallell to RA) and I balance the RA out it will always try to go back to it's horizontal position, or at least as soon as I get near the "top". When I adjust the DEC then it's even worse and I will always feel some sort of drag in either direction, I'll try to make a video today, is probably the easiest way to show it.



#8 kathyastro

kathyastro

    Surveyor 1

  • *****
  • Posts: 1,830
  • Joined: 23 Dec 2016
  • Loc: Nova Scotia

Posted 03 June 2020 - 08:23 AM

Okay, so the orientation of my DEC will not affect the balance of my RA? I mean now that I think about it it's obvious that it won't, since there's the same force working on both ends, as long as the counter bar is horizontal. But as soon as I change the orientation to point at my target it will obviously start to try and get back into the horizontal position right?

If dec is out of balance, it will affect RA.  Imagine the scope is horizontal, as though you were looking at something to the west.  If the camera end is heavy, it will want to pull the east side down, pulling the RA against the tracking.  And the opposite of course if you are looking east.  The effect is worst when pointing due east or due west, but it will be there for most of the sky.

 

You should balance both axes.  I would de-emphasize what I said earlier about dec balance not being critical.  It isn't critical, but it is important enough to have a measurable effect.


  • Orangeray likes this

#9 kathyastro

kathyastro

    Surveyor 1

  • *****
  • Posts: 1,830
  • Joined: 23 Dec 2016
  • Loc: Nova Scotia

Posted 03 June 2020 - 08:26 AM

it will always try to go back to it's horizontal position

If it "tries" to go anywhere, it is not in balance.  A balanced scope will stay in whatever position you leave it.
 



#10 Orangeray

Orangeray

    Lift Off

  • -----
  • topic starter
  • Posts: 16
  • Joined: 06 Jun 2019

Posted 03 June 2020 - 11:36 AM

If dec is out of balance, it will affect RA.  Imagine the scope is horizontal, as though you were looking at something to the west.  If the camera end is heavy, it will want to pull the east side down, pulling the RA against the tracking.  And the opposite of course if you are looking east.  The effect is worst when pointing due east or due west, but it will be there for most of the sky.

 

You should balance both axes.  I would de-emphasize what I said earlier about dec balance not being critical.  It isn't critical, but it is important enough to have a measurable effect.

 Okay yeah I think I got it. Since the DEC is adjusted by loosening two screws and turning the whole thing I never actually thought about balancing that one out. But yeahh, that makes totally sense now that I think about it. I adjusted the position of the scope on the dovetail as close to the center of the DEC and now it seems already a lot better.

 

 

If it "tries" to go anywhere, it is not in balance.  A balanced scope will stay in whatever position you leave it.
 

It's still moving a little bit in certain positions now but already feels a lot better! And I really hope I didn't already screw up my RA motor in the 4 nights of imaging since it was probably pushing against some heavy forces frown.gif

 

 

UPDATE:

Okay I just found some sort of dovetail adapter that I can use to adjust the position of the telescope freely. (Before I was limited to the spacing in the dovetail) Now I managed to get it pretty balanced out. Still moving a little bit in certain positions but I feel like for that kind of mount that is acceptable since all of the connections might be a little bit off center anyway and put some forces here and there? Here's a picture of how it looks now (the above picture was stolen from Astrobackyards Setup)

 

JInFJqi.jpg

It's a pretty unstable setup in my opinion so I might manufacture an adapter part myself which will be a single piece of metall to make it more stable.


Edited by Orangeray, 03 June 2020 - 12:32 PM.


#11 Huangdi

Huangdi

    Viking 1

  • *****
  • Posts: 543
  • Joined: 24 Jul 2019

Posted 03 June 2020 - 12:26 PM

What's the point in balancing DEC on a Mount without a DEC axis?

 

I'd simply balance RA so that it's slightly heavy to make tracking easier and be done with it. I never had any balancy issues with my Star Adventurer and could do 3-5min guided subs at 300mm FL with 3.5kg loaded up there.

 

You will need to adjust the balance bias depending on where in the sky you're imaging.



#12 Orangeray

Orangeray

    Lift Off

  • -----
  • topic starter
  • Posts: 16
  • Joined: 06 Jun 2019

Posted 03 June 2020 - 12:36 PM

What's the point in balancing DEC on a Mount without a DEC axis?

 

I'd simply balance RA so that it's slightly heavy to make tracking easier and be done with it. I never had any balancy issues with my Star Adventurer and could do 3-5min guided subs at 300mm FL with 3.5kg loaded up there.

 

You will need to adjust the balance bias depending on where in the sky you're imaging.

 

That's what I thought as well. But if you look at my photo of the setup above and imagine the telescope is sitting at the very back of the dovetail (which it was in the beginning) if you turn the camera to the right or left it will be totally out of balance and start to put on forces on the RA. At least that's what I learned in the last hour or so of trying it out :D
 

Adjusting the balance depending on where in the sky I'm imaging is something I thought of as well but since the mount will keep moving the amount of forces that act against it will increase with time I guess. Maybe it's not enough to make a difference but balancing it out for every position also makes it way easier to point the camera at any point in the sky since there are no forces trying to act against your movement.


  • kathyastro likes this

#13 Huangdi

Huangdi

    Viking 1

  • *****
  • Posts: 543
  • Joined: 24 Jul 2019

Posted 03 June 2020 - 12:56 PM

That's what I thought as well. But if you look at my photo of the setup above and imagine the telescope is sitting at the very back of the dovetail (which it was in the beginning) if you turn the camera to the right or left it will be totally out of balance and start to put on forces on the RA. At least that's what I learned in the last hour or so of trying it out :D

Adjusting the balance depending on where in the sky I'm imaging is something I thought of as well but since the mount will keep moving the amount of forces that act against it will increase with time I guess. Maybe it's not enough to make a difference but balancing it out for every position also makes it way easier to point the camera at any point in the sky since there are no forces trying to act against your movement.


The goal is to assert rough balance. Once you achieved that, you want to bias the balance (assuming you are guiding. If not you just want rough balance) do that the gears are always engaged into one direction

#14 kathyastro

kathyastro

    Surveyor 1

  • *****
  • Posts: 1,830
  • Joined: 23 Dec 2016
  • Loc: Nova Scotia

Posted 03 June 2020 - 01:33 PM

The goal is to assert rough balance. Once you achieved that, you want to bias the balance (assuming you are guiding. If not you just want rough balance) do that the gears are always engaged into one direction

A little bit of a bias in RA is okay.  But as I pointed out in post #8, your dec needs to be balanced even if it is not motorized.  Otherwise it will affect you RA balance, sometimes assisting the bias, sometimes fighting it, depending on where in the Sky you are aiming.


Edited by kathyastro, 03 June 2020 - 01:35 PM.

  • Orangeray likes this

#15 Huangdi

Huangdi

    Viking 1

  • *****
  • Posts: 543
  • Joined: 24 Jul 2019

Posted 03 June 2020 - 02:55 PM

A little bit of a bias in RA is okay.  But as I pointed out in post #8, your dec needs to be balanced even if it is not motorized.  Otherwise it will affect you RA balance, sometimes assisting the bias, sometimes fighting it, depending on where in the Sky you are aiming.

Well of course you wouldn't want the "DEC" axis to be completely out of balance. But it shouldn't require any fine tuning in my experience. 


  • Orangeray likes this

#16 Orangeray

Orangeray

    Lift Off

  • -----
  • topic starter
  • Posts: 16
  • Joined: 06 Jun 2019

Posted 04 June 2020 - 01:04 AM

You will need to adjust the balance bias depending on where in the sky you're imaging.

I just found this video, was uploaded yesterday right as we were discussing this topic :D Is that what you meant with balancing the DEC out for a certain position at the sky?




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





Also tagged with one or more of these keywords: astrophotography, beginner, refractor, dslr



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics