Jump to content

Banner.jpg.b6007b69ccdf5c69bf18273ddfe023df.jpg

Need help with collimation.


Recommended Posts

Hi, I’ve been observing the moon in the day and no matter what I do it feels like I just can’t find that perfect focus. I’ve researched and people say it’s mainly down to collimation. Here is the view I see through my collimation cap, my focuser is backed all the way out: 

8EF7CDAC-D058-434C-B2CE-188C3509B428.jpeg

208F317B-0A25-4BD8-B65A-71F76F04E020.jpeg

Link to comment
Share on other sites

It's quite difficult to tell what's going on there. I think maybe the secondary is slightly rotated away. The secondary shadow gives it away the most. Do you have a cheshire/sight tube or concenter? You really do need one of those tools to collimate the secondary, a collimation cap is really only of use for the primary after the secondary is collimated.

With regards to getting a sharp focus, there are also other factors that can have a far greater effect than collimation so don't get too hung up over it.

  • What eyepiece(s) are you having trouble focusing with? Is it the standard 10mm MA supplied with Skywatcher scopes? If so I would suspect that to be at least part of the issue.
  • Are you giving your scope long enough to cool down before trying high power observing? You will probably have tube currents in the scope for at least half an hour after you get it out which will impact the views.
  • What are you putting the scope on? Concrete and the like hold on to heat for longer than the garden lawn and with the scope being so close to the ground, ground thermals are going to be more of an issue.
  • What are you observing over? If you're pointing your scope over buildings then again thermals coming off the buildings are going to cause problems. Trying to observe when the Moon is over fields or gardens will improve things. If you are observing over buildings, moving your scope back as far as possible so that the Moon appears as high over the rooftops as possible will be useful.
Link to comment
Share on other sites

1 hour ago, Ricochet said:

It's quite difficult to tell what's going on there. I think maybe the secondary is slightly rotated away. The secondary shadow gives it away the most. Do you have a cheshire/sight tube or concenter? You really do need one of those tools to collimate the secondary, a collimation cap is really only of use for the primary after the secondary is collimated.

With regards to getting a sharp focus, there are also other factors that can have a far greater effect than collimation so don't get too hung up over it.

  • What eyepiece(s) are you having trouble focusing with? Is it the standard 10mm MA supplied with Skywatcher scopes? If so I would suspect that to be at least part of the issue.
  • Are you giving your scope long enough to cool down before trying high power observing? You will probably have tube currents in the scope for at least half an hour after you get it out which will impact the views.
  • What are you putting the scope on? Concrete and the like hold on to heat for longer than the garden lawn and with the scope being so close to the ground, ground thermals are going to be more of an issue.
  • What are you observing over? If you're pointing your scope over buildings then again thermals coming off the buildings are going to cause problems. Trying to observe when the Moon is over fields or gardens will improve things. If you are observing over buildings, moving your scope back as far as possible so that the Moon appears as high over the rooftops as possible will be useful.

Hi, thanks for your reply. I don’t have a Cheshire, only a collimating cap. Everything appears circular and concentric through the eye piece but it’s hard to look through a pinhole so I don’t see very much. I am using a 25mm eye piece. I gave my telescope an hour to reach equilibrium to the temperature outside. My telescope was on concrete looking straight above. (The moon is quite high in orbit currently). I did see less more detail the more I looked. I got a couple pictures of the moon through the telescope through my phone by just holding it up to the ep which I think don’t really do it justice and I also drew on some circles to my previous image. 

1FD4C0C4-DD47-4BAD-92F2-0663B46EA745.jpeg

955E72E4-8760-48BA-B221-48723F2DEE40.png

3EC4000E-3F52-42A6-B329-5BFC80CFE70B.png

Link to comment
Share on other sites

1 hour ago, Ricochet said:

It's quite difficult to tell what's going on there. I think maybe the secondary is slightly rotated away. The secondary shadow gives it away the most. Do you have a cheshire/sight tube or concenter? You really do need one of those tools to collimate the secondary, a collimation cap is really only of use for the primary after the secondary is collimated.

With regards to getting a sharp focus, there are also other factors that can have a far greater effect than collimation so don't get too hung up over it.

  • What eyepiece(s) are you having trouble focusing with? Is it the standard 10mm MA supplied with Skywatcher scopes? If so I would suspect that to be at least part of the issue.
  • Are you giving your scope long enough to cool down before trying high power observing? You will probably have tube currents in the scope for at least half an hour after you get it out which will impact the views.
  • What are you putting the scope on? Concrete and the like hold on to heat for longer than the garden lawn and with the scope being so close to the ground, ground thermals are going to be more of an issue.
  • What are you observing over? If you're pointing your scope over buildings then again thermals coming off the buildings are going to cause problems. Trying to observe when the Moon is over fields or gardens will improve things. If you are observing over buildings, moving your scope back as far as possible so that the Moon appears as high over the rooftops as possible will be useful.

Yup. Of the ep’s are stock from the skywatcher 200p. The 25mm view is just slightly blurry but the 10mm view is pretty blurry. I see wayyy more detail in the 25mm than the 10mm because the 10mm just looks too blurry when I’m viewing.

Link to comment
Share on other sites

12 hours ago, Daniel_J said:

Hi, thanks for your reply. I don’t have a Cheshire, only a collimating cap. Everything appears circular and concentric through the eye piece but it’s hard to look through a pinhole so I don’t see very much. I am using a 25mm eye piece. I gave my telescope an hour to reach equilibrium to the temperature outside. My telescope was on concrete looking straight above. (The moon is quite high in orbit currently). I did see less more detail the more I looked. I got a couple pictures of the moon through the telescope through my phone by just holding it up to the ep which I think don’t really do it justice and I also drew on some circles to my previous image. 

To be honest it's wise to invest in the tools for the task.  A cheshire or Hotech  collimator and a self centring adapter makes the task of collimation a lot easier. 

Rather than using the moon, do a star  test.   Find a bright star, then rack the focus to both extremes and look for the pattern of detraction rings that form.  If they are concentric like the image below then the scope is collimated

2115096473_airyrings.png.a07c9a09dde8c0c7940f3058511c2b70.png

Link to comment
Share on other sites

3 minutes ago, malc-c said:

To be honest it's wise to invest in the tools for the task.  A cheshire or Hotech  collimator and a self centring adapter makes the task of collimation a lot easier. 

Rather than using the moon, do a star  test.   Find a bright star, then rack the focus to both extremes and look for the pattern of detraction rings that form.  If they are concentric like the image below then the scope is collimated

2115096473_airyrings.png.a07c9a09dde8c0c7940f3058511c2b70.png

Thank you! I’ve been meaning to do a star test but it’s been cloudy for a week now and I’m very impatient so I’ve just been viewing the moon in the day when it’s mostly clear. I did do a star test a while ago and it looked similar to that picture so I think it was just my viewing conditions. I think through the collimation cap the mirrors seem aligned but I do need to do a star test asap.

Link to comment
Share on other sites

1 hour ago, Spile said:

The alignment looks fine to me but I would recommend a Cheshire eyepiece and sight tube combination tool to confirm as per https://astro.catshill.com/collimation-guide/

Thank you, that guide looks amazing so I’ll definitely try it tomorrow when i get the chance. The moon definitely looked a lot sharper today when I was viewing it. Possibly due to better viewing conditions. 

Link to comment
Share on other sites

Yes, I wondered about the conditions. I was looking at the moon yesterday and the seeing was moderately poor from central Bristol - I guessed warm air preventing the airborne pollution from clearing. Always worth looking at an object on successive days.

Link to comment
Share on other sites

6 hours ago, Giles_B said:

Yes, I wondered about the conditions. I was looking at the moon yesterday and the seeing was moderately poor from central Bristol - I guessed warm air preventing the airborne pollution from clearing. Always worth looking at an object on successive days.

For sure, here in Liverpool it's been really cloudy for a week or so causing me to be impatient and looking at the moon during the day. I think its the asphalt radiating heat during the day causing turbulence making the moon appear relatively blurry. 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.